Download Kinetics Workbook - School District 67

Kinetics Workbook
for
Chemistry 12
Period
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1
2
3
4
5
6
7
8
9.
Monitoring Reaction Rates
Factors that Change the Rate
Collision Theory
PE Diagrams
Mechanisms
Lab: The Iodine Clock Reaction
Review
Review
Test
Worksheets
Quiz
WS 1
WS 2
WS 3
WS 4
WS 5
Internet Review
Practice Test 1
Practice Test 2
Q1
Q2
Q3
Q4
Q5
This workbook will allow you to demonstrate your understanding of all aspects of the kinetics
unit. The minimum expectation is that you do all of these questions by the due dates given by your
teacher. Do the questions. Use your notes from class to assist you. Then after you have finished go to the
web site to evaluate your work. Make a list of those things that you do not quite understand and bring
them to class. Your instructor will review them. There are other things that you should do to prepare for
the test at the end of the unit. Remember, what you put into this course is what you will get out. There is
no substitute for consistent effort and hard work. If you cannot do a question, get some help before the
end of the unit, you need to know, understand, and remember everything. Good luck! I know you can do
well in this unit.
1
WS #1
1.
2.
2.
3.
i)
Monitoring and Calculating Reaction Rates
Read the chapter from your textbook on Kinetics over the next week. “A” students should read it
twice.
a) When measuring a property associated with a reactant in a reaction, does it increase or
decrease?
b) When measuring a property associated with a product in a reaction, does it increase or
decrease?
Give three ways to measure the rate of the following reaction. State the specific properties that you
would monitor and include units (amount is not a specific property). State if each property would
increase or decrease. Describe in each case how you would calculate the reaction rate.
2HNO3(aq)
+ Cu(s)
→ NO2(g)
The first one is done for you.
+ H2O(l) + CuNO3(aq)
Mass of Cu
Decrease
Grams
Rate = mass/time
ii)
iii)
4.
Calculate the rate in units of (g Cu/min).
Mass of copper (g)
3.26
Time (min)
5.0
2.93
7.0
2.61
9.0
5.
Calculate the rate in units of (mole Cu/min).
6.
Calculate the rate in moles HNO3 consumed per second (remember that 2 moles are consumed per
1 mole of Cu).
7.
Calculate the rate in units of (g/sec) for HNO3.
8.
Calculate the rate in units of (mL NO2/sec).
2HNO3(aq) + Cu(s) → NO2(g) + H2O(l) + CuNO3(aq)
Volume of NO2 (mL)
10.0
11.5
Time (sec)
0.00
5.00
9.
12.7
10.00
Calculate the rate in units of (L NO2/min).
2
10.
Calculate the rate in units of (moles NO2/min) at STP.
11.
Calculate the rate in units of (moles HNO3/min) at STP (remember that 2 moles are consumed per
1 mole of NO2)
12.
Calculate the rate of the following reaction:
2NO (g) +
2H2 (g) →
N2 (g) +
2H2O (g)
mole
NO
Time(s)
0.080
0.060
0.040
0.020
0.00
2.0
4.0
6.0
8.0
10.0
12.0
a)
What is the rate in moles NO per second?
b)
What is the rate in moles N2 per second?
3
c)
What is the rate in grams NO per min?
d)
What is the rate in grams N2 per hour?
13.
Choose three properties that you could measure in order to monitor the rate of the following
reaction.
Cu (s) + 2AgNO3 (aq) → 2 Ag (s) + Cu(NO3)2 (aq)
Property
Unit of Measurement
Change
i.
ii.
iii.
14.
Calculate the rate of the following reaction in units of M/s:
Zn(s) + 2HCl(aq) → ZnCl2(aq) +
Molarity of HCL (M)
time (seconds)
15.
0.612
21.0
0.813
25.0
1.05
29.0
Calculate the rate of the following reaction in L/min:
Zn(s) + 2HCl(aq)
16.
H2(g)
→
ZnCl2(aq) +
H2(g)
Volume of H2 (L)
0.255
0.550
0.790
Time (min)
1.0
2.0
3.0
If 0.369 g of HCl is neutralized with 0.250 M NaOH in 25.0 seconds, what is the reaction rate in
moles HCl /min.
4
WS # 2
Factors That Change The Reaction Rate
Homogeneous reactions
Reactants are in the same phase (aq), (g) , or (l) and are thoroughly mixed.
Heterogeneous reactions
Reactants are in the two or more phases and are not thoroughly mixed (two solids do not mix).
Classify as Homogeneous or Heterogeneous:
1.
Zn(s) + 2 HCl(aq)
→
H2 (g) + ZnCl2 (aq)
2.
Ag+(aq) + Cl-(aq)
→
AgCl (s)
3.
H2(g) + F2(g)
→
2HF(g)
4.
2Al(s) + 3I2(s)
→
2AlI3(s)
The following four factors will increase the rate of a chemical reaction that is homogeneous:
1.
2.
3.
4.
The above four factors as well as the two below will increase the rate of a heterogeneous reaction:
5.
6.
For each reaction specifically describe all of the ways to increase the reaction rate
(i.e.. increase [H2]).
1.
H2 (g) + F2 (g) → 2 HF (g)
2.
3.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O (l)
Zn(s) + 2HCl(aq)
→
H2(g) + ZnCl2(aq)
5
4.
State three examples of chemical reactions that are desired to be slow.
5.
Give three examples of chemical reactions that are desired to be fast.
6.
List all of the ways to increase the rate of the following reaction:
2H2O2(aq) → 2H2O(l) + O2(g)
I.
Homogeneous reactions are generally faster than heterogeneous- the reactants are mixed better
and therefore there are more collisions between reactant particles.
HCl(aq) + NaOH(aq) →
is
Zn(s) + 2HCl(aq)
II.
NaCl(aq) + H2O(l)
faster than
→
H2(g) + ZnCl2(aq)
Simple ionic reactions (where there are no bonds to break) are generally faster than more
complex ionic reactions (where there are bonds to break).
Pb+2(aq) + 2Cl-(aq) → PbCl2(l)
is
faster than
2Na+(aq) + 2ClO-(aq) → 2Na+(aq) + 2Cl-(aq)
+ O2(g)
Solid reactants are slower than gases, which are slower than aqueous.
1.
Indicate the faster and slower reaction and explain why.
a)
2Al(s) + 3I2(s)
→
2AlI3(s)
b)
Ag+(aq) + Cl-(aq)
→
AgCl(s)
6
2.
Indicate the faster and slower reaction and explain why.
a)
2Al(s) + 3I2(s)
b)
2Na+(aq) + 2ClO-(aq) →
3.
Indicate the faster and slower reaction and explain why.
a)
3Ba+2(aq) + 2PO4-3(aq)
b)
Cu(s) + 2Ag+(aq)
WS # 3
1.
→
2AlI3 (s)
2Na+(aq) + 2Cl-(aq)
→
→
+ O2(g)
Ba3(PO4)2(aq)
Cu+2 (aq) + 2Ag(s)
Collision Theory
2.
Chemical reactions are the result of _________________ between reactant particles, where
_________________ are broken and new ones form.
A successful collision requires _____________________ and __________________ .
3.
Describe as fast, medium or slow. Explain!
i)
2 H2 (g) + O2 (g)
_______
_______
4.
2 H20 (l) (room temperature)
_______________________________________________________
2 Ag+ (aq) + CO32- (aq)
ii)
iii)
→
→
Ag2CO3
(s)
_______________________________________________________
2 HCl (aq) + Na2CO3 (aq)
→
CO2 (g) + 2 NaCl (aq) + H20 (l)
_______ _______________________________________________________
i)
Describe how you would measure the rate of the reaction :
Zn(s) + 2 HCl(aq)
ii)
→
ZnCl2(aq) + H2(g)
________________________________________________________________
List four ways to increase the rate.
________________________________________________________________
________________________________________________________________
7
5.
A 10 °C temperature increase frequently doubles the rate of a slow reaction because:
a) The temperature has doubled.
b) The PE of the colliding particle has doubled.
c) The KE of the colliding particle has doubled.
d) The fraction of particles with sufficient KE to react has doubled.
6.
Both collisions A and B have the same KE. Which collision is successful and explain why.
Before Collision
After Collision
A)
B)
________________________________________________________________
________________________________________________________________
7.
Use the collision theory to explain how each factor increases the reaction rate.
i)
Increasing temperature
ii)
iii)
iv)
v)
Increasing [reactants]
Increasing surface area (solid)
Agitation of a heterogeneous reaction
Adding a catalyst
i)
_________________
_________________
ii)
_________________
iii)
_________________
iv)
_________________
v)
_________________
_________________
8
8.
Explain why collision A was successful while collision B was unsuccessful.
Before Collision
After Collision
A)
B)
________________________________________________________________
________________________________________________________________
Explain each of the following using the collision theory. You need to explain each statement.
9.
A candle is not burning at room temperature
A match lights the candle
The candle continues to burn
10.
H2O2 decomposes slowly at 20o C
KI is added and rapid decomposition begins
The temperature increases
11.
H2 and O2 in a balloon do not react
A spark ignites the balloon
9
An explosion results
12.
CH4 and O2 in a balloon do not react
A platinum gauze ignites the balloon
An explosion results
13.
N2(g) + O2(g)
→
2NO(g)
Even though there are more than four billion collisions per second between N and O the amount of
product after a year is too small to detect. Using the collision theory, give two reasons why this
reaction might be slow.
i)
ii)
14.
Give two reasons why some collisions will not result in a chemical reaction.
i)
ii)
15.
Give five reasons that might account for the following reaction having a high rate.
Ca (s) + 2HCl (aq)
→ CaCl2 (aq) + H2 (g)
i)
ii)
iii)
iv)
v)
16.
C(s) + O2(g) → CO2(g)
List four ways the rate of the reaction could be increased.
i)
ii)
iii)
iv)
10
17.
State the relationship between Activation energy and the rate of a reaction. Graph the relationship.
Rate
Activation Energy
18.
State the relationship between Temperature and the rate of a reaction. Graph the relationship.
Rate
Temperature
19.
State the relationship between Concentration and the rate of a reaction. Graph the relationship.
Rate
Molarity
11
20.
Give three examples of reactions that are desired to be slow.
a)
b)
c)
21.
Give three examples of reactions that are desired to be fast.
a)
b)
c)
22.
List all of the ways to increase the rate of the reaction:
2 H2O2(aq) → 2 H2O(l) + O2(g)
23.
Describe how you could measure the rate of the reaction above. State the property you would
measure and describe how it changes. Draw a diagram to illustrate your answer.
24.
Pick the fastest and the slowest reaction at 20 °C.
a) H2(g) + I2(g) →
2 HI(g)
b) 2 HCl(aq) + Na2CO3(aq)
2+
c) Hg
(aq)
+ 2
I -(aq)
→
→
CO2(g) + 2 NaCl(aq) + H2O(l)
HgI2(s)
25.
H2 and O2 can exist at 20 °C for years without reacting. But when a small spark ignites the mixture
it reacts explosively. Explain using the Collision Theory.
26.
Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of
collisions and the x-axis is collision energy. Draw the Ea line showing about 10% of the collisions
12
having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient
energy.
Faction of
collisions
Collision Energy
27.
Shade in the area of the collision energy distribution diagram showing those collisions that do not
have the required energy to be successful at the temperature below.
Faction of
collisions
Collision Energy
Ea
26.
Shade in the area of the collision energy distribution diagram showing those collisions that do
have the required energy to be successful at the temperature below. Redraw the curve at a higher
temperature.
13
Faction of
collisions
Collision Energy
Ea
Kinetics - Descriptions
Use the collision theory to explain the following. Each sentence must be explained with a statement from
the collision theory.
1.
A unlit candle does not burn. It burns after being lit with a match. It continues to burn.
2.
A solution is reacting very slowly to produce bubbles. KI is added and although it is not consumed
in the reaction, it speeds up the reaction rate. The temperature increases. The rate increases even
more.
14
3.
Iron reacts slowly with HCl. Iron is replaced with Zn and a much more vigorous reaction rate
occurs.
4.
H2 and O2 can exist together for years at room temperature without reacting. A spark begins the
reaction. An explosion results.
5.
Dilute nitric acid shows little reaction with copper. Concentrated nitric acid vigorously reacts.
6.
Water puts out a fire.
7.
Paint prevents rusting.
8.
A preservative in food slows rotting.
15
WS # 4
1.
Potential Energy Diagrams Worksheet
Draw the PE diagram showing the PE changes that occur during a successful collision of the
exothermic reaction:
H2 + I2
→
2 HI + 250 kJ
The PE of the reactants = 400 kJ
Ea = 200 kJ
PE
Reaction
Path
2.
Draw the PE diagram showing the PE changes that occur during a successful collision of the
endothermic reaction:
A + B + 200 kJ →
C
The PE of the reactants = 200 kJ
The Activation Energy in the forward direction = 250 kJ
PE
Reaction
Path
16
3.
Write the following reaction in ΔH notation.
A + B + 200 kJ →
4.
Write the following reaction in Standard Notation.
H2
5.
+
I2
→
2 HI
ΔH = -250 kJ
Write in Standard Notation.
2NI3 + 3BaCl2 →
6.
C
2NCl3
+ 3BaI2
ΔH = 175 kJ
Write in ΔH notation.
2AlBr3 + 3BaF2
→
2AlF3
+ 3BaBr2 + 276 kJ
Draw the potential energy diagram for the following reactions.
7.
Potential energy of reactants =
Potential Energy of activated complex =
Potential Energy of the products =
250 kJ
350 kJ
300 kJ
PE
Reaction
Path
17
a)
b)
c)
d)
e)
f)
g)
h)
How does the potential energy change as the reaction proceeds?
How does the kinetic energy change as the reaction proceeds?
Is the reaction exothermic or endothermic?
What is the value of ΔH?
If a catalyst was added, what would happen to the potential
energies of the:
Reactants?
Products?
Activated Complex?
If a catalyst were added what would happen to the rate?
Draw the potential energy diagram for the following reactions.
8.
Potential energy of reactants =
Activation Energy =
350 kJ
100 kJ
PE
Reaction Path
Potential Energy of the products =
a)
b)
c)
d)
250 kJ
How does the potential energy change as the reaction proceeds?
How does the kinetic energy change as the reaction proceeds?
Is the reaction exothermic or endothermic?
What is the value of ΔH?
If the concentration of the reactants was increased, what would happen to the energies of the:
e)
f)
g)
h)
Reactants?
Products?
Activated Complex?
What would happen to the rate?
18
Draw the potential energy diagram for the following reactions.
PE
9.
Potential energy of reactants =
Potential Energy of activated complex =
ΔH =
a)
b)
c)
d)
How does the potential energy change as the reaction proceeds?
How does the kinetic energy change as the reaction proceeds?
Is the reaction exothermic or endothermic?
What is the value of ΔH?
If the temperature was increased, what would happen to the energies of the:
Reactants?
Products?
Activated Complex?
What would happen to the rate?
e)
f)
g)
h)
200 kJ
400 kJ
150 kJ
Reaction
Path
19
PE
Reaction Path
10.
Potential energy of products =
Potential Energy of activated complex =
ΔH=
a)
b)
c)
d)
50 kJ
400 kJ
-50 kJ
How does the potential energy change as the reaction proceeds?
How does the kinetic energy change as the reaction proceeds?
Is the reaction exothermic or endothermic?
What is the value of ΔH?
If the surface area of the reactants was increased, what would happen to the energies of the:
e)
f)
g)
h)
Reactants?
Products?
Activated Complex?
What would happen to the rate?
11.
What is the only thing, other than changing the reaction that will change the potential energy
diagram? Describe how it will affect the diagram and the rate.
20
12.
Label each interval on the potential energy diagram.
a
b
c
d
e
a)
PE
b)
c)
d)
Reaction Path
e)
13.
Label each interval on the potential energy diagram.
a
b
c
d
e
PE
Reaction Path
a)
b)
c)
d)
e)
21
Ws # 5 Mechanisms
→
→
→
OCl- + H2O
HOCl + IHOI + OH-
1.
i)
ii)
iii)
HOCl + OHHOI + ClH2O + OI-
The net chemical equation is:
The reaction intermediates are:
The catalyst is:
Br2
→
Br + OCl2
Br + Cl
2.
2Br
→
→
BrOCl +
BrCl
Cl
fast
slow
fast
i)
ii)
iii)
iv)
The net chemical equation is:
The reaction intermediates are:
The rate-determining step is
If the concentration of Br2 is increased will the rate of the reaction increase? Explain your
answer.
v)
If the concentration of OCl2 is increased will the rate of the reaction increase? Explain your
answer.
3.
The mechanism for the catalytic decomposition of formic acid is shown below.
step 1
HCOOH + H+
step 2
[HCOOHH]+
step 3
[HCO]+
→ [HCOOHH]+
→
→
[HCO]+
CO
+ HOH
+ H+
The potential energy diagram is:
190
PE
180
170
160
150
22
Reaction Path
i)
The catalyst is
ii)
The rate determining step is
iii)
ΔH =
iv)
The reverse activation energy is
v)
The enthalpy of [HCOOHH]+ is
vi)
Is the reaction exothermic or endothermic?
vii)
Which chemical formula has the greatest potential energy?
vii)
Which chemical formula has the greatest kinetic energy?
ix)
Does this reaction absorb or release kinetic energy?
4.
Define and remember the following definitions.
Mechanism
Activation energy
Rate determining step
Catalyst
Reaction intermediate
Endothermic
Exothermic
Activated complex
ΔH
Reaction rate
5.
The catalyzed decomposition of acetaldehyde has an overall reaction of:
CH3CHO → CH4
+ CO . Determine step 2 of the reaction mechanism.
A proposed mechanism is:
step 1
CH3CHO
+
I2 →
CH3I + HI + CO
step 2
23
6.
The following reaction has an overall reaction of:
2Ce4+
+
→
Tl+
2Ce3+
+
Tl3+
Determine step 2 of the reaction mechanism.A proposed mechanism is:
step 1
Ce4+
+
Mn+2
→
Ce3+
+
Mn3+
Mn4+
+
Tl+
→
Tl3+
+
Mn2+
step 2
step 3
7.
A reaction has a overall equation of: Br2 + OCl2 → BrOCl + BrCl .
Determine step 3 of the mechanism.
step 1
Br2 → 2Br
step 2
Br + OCl2 →
BrOCl
+ Cl
step 3
List two intermediates:
8.
Complete the following mechanism.
step 1
NO +
→
Pt
NO →
step 2
NOPt +
step 3
O2Pt
→
O2
overall
2NO →
N2
+
+ Pt
+ O2
Identify the catalyst
Identify the two intermediates
9.
Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of
collisions and the x axis is collision energy. Draw the Ea line showing about 10% of the collisions
having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient
energy.
24
Fraction of
collisions
Collision Energy
25
Kinetics Quiz #1
1.
Consider the following Reaction: HCl(aq) + NaOH(aq) → H2O(1) + NaCl (aq) The rate of this
reaction could be determined by monitoring the change of concentration of :
A.
B.
C.
D.
2.
0.0013 mol/s
0.0020 mol/s
0.0030 mol/s
0.0060 mol/s
Consider the following reaction: Zn(s) + 2HCl (aq) → ZnCl 2(aq) + H 2(g)
Solid zinc was added to 1.0 M HCl. In 20.0 s. the temperature of the container increased by
0.05oC and 25.00 ml of H2 was produced. The rate was:
A.
B.
C.
D.
4.
H+
Cl Na +
H2O
Consider the following reaction: 2Al (5) + 6HCl (aq) → 2AlCl 3(aq) + 3H 2(g)
A 0.040 mole piece of aluminum reacted completely in 20 s. The rate of formation of hydrogen
gas is :
A.
B.
C.
D.
3.
Monitoring Reaction Rates
0.5oC
1.0 M HCl/s
1.25 ml H2/s
0.050 mol HCl/s
Consider the following reaction: N 2(g) + 3H 2(g) → 2NH 3(g)
If the rate of formulation of NH3 is 9.0 x 10–4 mol/s, then the rate of consumption of N2 is:
A.
B.
C.
D.
4.5 x 10-4 mol/s
6.0 x 10-4 mol/s
9.0 x 10-4 mol/s
1.4 x 10-3 mol/s
5.
In general, the reaction rates double when the temperature is increased by 10oC . The temperature
of a reaction is increased by 40oC. The rate of the reaction will be increased by:
A.
2
B.
4
C.
8
D.
16
6.
Consider the following reaction: 2NO2(g) → 2NO(g) + O2(g)
Under certain conditions, the rate of decomposition of NO2 is 3.2 x 10-3 mol/s. The rate of the
formation of O2 is:
A.
B.
1.6 x 10-3 mol/s
3.2 x 10-3 mol/s
26
C.
D.
7.
An 8.00 g piece of magnesium was placed into 6.0 M HCl . After 25 s. 3.50 g of unreacted
magnesium remained. The average rate at which magnesium was consumed is:
A.
B.
C.
D.
8.
50.0 mL/80s
50.0 mL/30oC
25.0 mL/80s
25.0 mL/30oC
A 25.0 mL sample of hydrogen peroxide decomposes producing 50.0 mL of oxygen gas in 137 s.
The rate of formation of O2 in mL/min is
A.
B.
C.
D.
12.
Mass of the system
Pressure of the gas
Concentration of H2O
Concentration of MgCO3
At 30oC a 25.0 mL sample of bleach decomposes producing 50.0 mL of oxygen gas in 80 seconds.
The rate of oxygen formation can be determined by the expression
A.
B.
C.
D.
11.
grams per mole.
Energy consumed per mole.
volume of gas per unit time.
moles formed per liter of solution
Consider the following reaction at a constant temperature in an open system:
MgCO3(s) + 2HCl(aq) → CO2(g) + H2O(l) + MgCl 2(aq)
Which of the following properties could be used to determine reaction rate?
A.
B.
C.
D.
10.
0.14 g/s
0.18 g/s
0.32 g/s
4.50 g/s
The rate of a chemical reaction can be expressed in
A.
B.
C.
D.
9.
4.8 x 10-3 mol/s
6.4 x 10-3 mol/s
0.182 mL/min
0.365 mL/min
10.9 mL/min
21.9 mL/min
Consider the following reaction:
2N2O5(g) → 4 NO2(g) + 02(g)
At a certain temperature the rate of decomposition of N2O5 is 2.5 x 10-6 mol/s. The rate of
formation of NO2 is
27
A.
B.
C.
D.
Kinetics
1.
Zn(s) + S(s) → ZnS(s)
Ba2+(aq) + SO42-(aq) → BaSO4(s)
NH3(g) + HCl(g) → NH4Cl(g)
2 Ag+(aq) + CO32-(aq) → Ag2CO3(s)
High kinetic energy
High activation energy
Catalytic effect on the reaction
Large surface area for the reaction
Consider the following reaction: 2H2O2(aq) → 2 H2O(l) + O2(g)
When 1.0 g of KI is added to the H2O2, bubbles of O2 are produced at an increased rate. When the
reaction is complete, the mass of KI is 1.0 g. The KI is a
A.
B.
C.
D.
4.
Factors that Change The Reaction Rate
Dust particles suspended in the air inside unheated grain elevators can sometimes react
explosively because the dust particles have a:
A.
B.
C.
D.
3.
Quiz #2
Which of the following reactions is the slowest at room temperature?
A.
B.
C.
D.
2.
1.0 x 10-5 mol/s
1.3 x 10-6 mol/s
2.5 x 10-6 mol/s
5.0 x 10-6 mol/s
Product
Catalyst
Reactant
Reaction Intermediate
Consider the following factors:
I.
II.
III.
Concentration of reactants.
Temperature of reactants.
Surface area of reactants.
The factors that affect the rate of a chemical reaction between two gases are
A.
B.
C.
D.
5.
I and II only
I and III only
II and III only.
I, II, and III
Consider the following reactions:
28
I.
II.
III.
N2(g) + O2(g) → 2NO(g)
2Mg(s) + O2(g) → 2MgO(s)
CaCO3(s) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
Increasing the surface area will increase the reaction rate in
A.
B.
C.
D.
6.
An untreated sugar cube does not burn when held over a lighted match. A sugar cube coated with
cigarette ash readily ignites and burns. All of the cigarette ash remains after the reaction. The
factor that caused this change in rate is the
A.
B.
C.
D.
7.
9.
Nature of reactants
Presence of a catalyst
Increase in surface area
Increase in concentration
Which combination of factors will affect the rate of the following reaction?
Zn(s) + 2HCl (aq) → ZnCl2(aq) + H2(g)
A.
B.
C.
D.
8.
II only
I and III only
II and III only
I, II and III
Temperature and surfaces only
Temperature and concentration only
Concentration and surface area only
Temperature, concentration, and surface area
To increase the rate of a reaction there must be an increase in
I
II
III
IV
frequency of successful collisions
volume of reaction vessel
pressure of the system
mass of the system
A.
B.
C.
D.
I only
I and III only
I, III and IV only
I, II, III and IV
Consider the following reaction:
2MnO4-(aq) + 5C2O42-(aq) + 16H+(aq) →
2Mn2+(aq) + 10CO2(g) + 8H2O(l)
The rate of decomposition of the oxalate ion is increased by
A.
B.
C.
Adding NaOH
Removing CO2
Adding a catalyst
29
D.
10.
Which of the following factors affect the rates of both homogeneous and heterogeneous reactions
I.
Nature of reactants
II.
Presence of a catalyst
III.
Temperature of system
IV
Concentration of reactants
A.
B.
C.
D.
11.
Kinetics
2.
Nature of reactants
Temperature of system
Surface area of reactants
Concentration of reactants
Consider the following reaction: 2S(s) + 302(g) → 2SO3(g) + heat
The rate of this reaction could be increased by
A.
B.
C.
D.
1.
I and IV only
II and III only.
II, III and IV only
I, II, III and IV
Which of the following factors affects the rate of heterogeneous reactions only.
A.
B.
C.
D.
12.
Decreasing the pressure.
Decreasing temperature
Adding a catalyst
Increasing the concentration of S(s)
Increasing the concentration of SO3(g)
Quiz #3
Collision Theory
Which of the following are necessary for successful collisions to occur?
I
II
III
Favorable collision geometry
Sufficient Kinetic energy
Large ∆H
A.
B.
C.
D.
I only
I and II only
II and III only
I, II, and III
Collision theory states that
30
A.
B.
C.
D.
3.
A catalyst increases the rate of a reaction by
A.
B.
C.
D.
4.
A decrease in surface area
A decrease in ∆H for the reaction
A decrease in the fraction of particles possessing sufficient energy
The introduction of an alternate pathway with greater activation energy
In general, a chemical reaction requiring a large activation energy will proceed
A.
B.
C.
D.
6.
Increasing the concentration of the reactant(s)
Decreasing the concentration of the reactant(s)
Increasing the activation energy of the overall reaction
Decreasing the activation energy of the overall reaction
Milk is refrigerated in order to slow the rate of decomposition by bacterial action. The decrease in
reaction rate is due to
A.
B.
C.
D.
5.
All collisions lead to chemical reactions
Most collisions lead to chemical reactions
Very few reactions involve particle collisions
Effective collisions lead to chemical reactions
At a fast rate
At a slow rate
Only at a low temperature
Only at low concentrations
Consider the following reaction:
Mg(s) + 2HCl(aq)
→ MgCl2(aq) + H2(g)
As the temperature of the above system is increased, the number of collisions
A.
B.
C.
D.
7.
The minimum amount of energy needed to start a reaction is called the
A.
B.
C.
D.
8.
Increases but fewer are effective
Decreases and fewer are effective
Increases and more are effective
Decreases but more are effective
Activation energy
Energy of a reaction
Entropy of a reaction.
Reaction mechanism energy
When a lit match is touched to the wick of a candle, the candle begins to burn. When the match is
removed, the candle continues to burn. In this reaction, the match
31
A.
B.
C.
D.
Behaves as a catalyst
Supplies activation energy
Is part of the rate-determining step
Lowers the activation energy barrier
32
9.
Consider the following collisions, each one occurring at the same temperature
Before Collision
F
Collision
After Collision
F
F
F
Collision 1
F
F
N
N
O
O
N
O
O
O
O
F
F
F
F
Collision 2
F
F
N
O
N
O
N
O
O
O
O
Before Collision
Collision
After Collision
33
Which one of the following factors explains why collision one is successful while collision two is
not successful?
A.
B.
C.
D.
10.
Catalyst
Geometry
Concentration
Kinetic energy
Consider the following factors
I
II
III
IV
Reactant particles collide
Sufficient kinetic energy is present
A favorable geometry exists
Catalysts are present
Which combination of the above factors is required for successful collisions
A.
B.
C.
D.
11.
To increase the rate of a reaction, there must be
A.
B.
C.
D.
12.
Decrease in the frequency of collisions
An Increase in the frequency of collisions.
A decrease in the frequency of successful collisions
An increase in the frequency of successful collisions
For collisions to be successful, reactants must have
A.
B.
C.
D.
Kinetics
1.
I only
II and III only
I, II, and III only
I, II, III, and IV
Favorable geometry only
Sufficient heat of reaction only
Sufficient potential energy only
Sufficient kinetic energy and favorable geometry
Quiz 4 Potential Energy Diagrams
The addition of a catalyst to a reaction provides an alternative mechanism with
A.
B.
C.
D.
Lower activation energy and lower reaction rate
Lower activation energy and higher reaction rate
Higher activation energy and lower reaction rate
Higher activation energy and higher reaction rate
34
Consider the following Reaction: ½ N2(g) + ½ O2(g) → NO(g) ∆H = +90 kJ/mol NO
The correct equation including the heat term is
2.
N2(g) + O2(g) + 90 kJ → 2NO(g)
N2(g) + O2(g) + 180 kJ → 2NO(g)
N2(g) + O2(g) → 2NO(g) +90kJ
N2(g) + O2(g) → 2NO(g) +180kJ
A.
B.
C.
D.
A forward reaction has activation energy of 50 kJ and a ∆H of –100 kJ.
3.
A
200
200
B
150
150
100
50
250
C
D.
200
100
300
150
100
The PE diagram, which describes this reaction, is
4.
Consider the following potential energy diagram
35
PE
(KJ)
175
100
50
Reaction Path
The Activation energy for the forward reaction is
A.
B.
C.
D.
5.
Consider the following reaction: ½ H2(g) + ½ I2(g) → HI(g)
The activation energy for the formation of HI is 167 kJ and for the decomposition of HI is 139 kJ.
The reaction for the formation of HI is
A.
B.
C.
D.
6.
25 kJ
50 kJ
75 kJ
125 kJ
Exothermic and the ∆H = -28 kJ
Exothermic and the ∆H = +28 kJ
Endothermic and the ∆H = -28 kJ
Endothermic and the ∆H = +28 kJ
Consider the following potential energy diagram
36
PE
I
III
IV
I
Reaction Path
The energy interval the represents the activation energy for the reverse reaction is
A.
B.
C.
D.
7.
As reactant molecules approach each other
A.
B.
C.
D.
8.
Heat is released
A reaction intermediate forms
Kinetic energy changes to potential energy
Potential energy changes to kinetic
Which of the following equations represents an endothermic reaction?
A.
B.
C.
D.
9.
I
II
III
IV
N204(g) + 59 kJ → 2NO2(g)
2H2(g) + 02(g) → 2H2O(l) + 572 kJ
2BrCl(g) – 29.3 kJ → Br2(g) + Cl2(g)
C(s) + O2(g) → CO2(g) ∆H = -394 kJ
Consider the following potential energy diagram
37
2
PE
4
1
3
Progress of Reaction
The interval representing ∆H for the reverse reaction is
A.
B.
C.
D.
1
2
3
4
10.
Which of the following corresponds to the fastest reaction at room temperature
A.
Increase slowly
B.
Remain constant
C.
Decrease slowly
D.
Increase rapidly due to alternate pathway
12.
Consider the following potential energy diagram that represents two different reactions. Which of
the following statements is correct?
A
A.
B.
C.
D.
B
Reactions A and B are both exothermic
Reactions A and B are both endothermic
Reaction A is exothermic and reaction B is endothermic
Reaction A in endothermic and reaction B is exothermic
38
13.
Consider the following reaction: ½ H2(g) + ½ I2(g) → HI(g) ∆H = +28 kJ
The activation energy for the formation of HI is 167 kJ. the activation energy for the
decomposition of HI is:
A.
B.
C.
D.
Kinetics
1.
28 kJ
139 kJ
167 kJ
195 kJ
Quiz #5
Mechanisms
Consider the following reaction mechanism
Step 1: M + X → MX
Step 2: MX + A → D + X
The chemical species MX is a(n)
A.
B.
C.
D.
2.
Catalyst
Inhibitor
Final Product
Reaction Intermediate
Consider the following reaction mechanism
Step 1: NO2 + NO2 → NO + NO3
Step 2: NO3 + CO → NO2 + CO2
The overall reaction is
A.
B.
C.
D.
3.
2NO2 → NO3 + NO
NO2 + CO → NO + CO2
NO3 + CO → NO2 + CO2
NO2 + NO3 + CO → NO3 + NO2 + NO + CO2
Consider the following reaction mechanism
Step 1:
Step 2:
V3+ + Cu2+ → V4+ + Cu+
Cu+ + Fe3+ → Cu2+ + Fe2+
(slow)
(fast)
The reaction intermediate is
A.
B.
C.
D.
4.
Cu+
Cu2+
V3+
Fe3+
Consider the following reaction Mechanism
39
Step 1: H2O2 + I - → H2O + IOStep 2: H2O2 + IO - → H2O + O2 + I The reaction intermediate is
A.
B.
C.
D.
5.
IIO H2O
H2O2
Consider the following potential energy diagram
PE
(kJ)
Progress of the reaction
The above potential energy diagram represents an
A.
B.
C.
D.
Exothermic reaction involving one step
Exothermic reaction involving two steps
Endothermic reaction involving one step
Endothermic reaction involving two steps
40
6.
Consider the following reaction mechanism
Step 1: NO2(g) + NO2(g) → NO(g) + NO3(g) (slow)
Step 2: NO3(g) + CO(g) → CO2(g) + NO2(g) (fast)
Which one of the following changes would result in the greatest increase in reaction rate
A.
B.
C.
D.
7.
Increase [CO]
Decrease [NO]
Increase [NO2]
Increase [NO3]
An uncatalyzed reaction was found to produce 40 kJ of energy in 10 mins. When catalyzed, the
same reaction produced 40 kJ of energy in 2 mins. Which one of the following potential energy
diagrams is consistent with the above data?
PE
A
B
PE
Reaction Path
C
PE
Reaction Path
D
Reaction Path
8.
PE
Reaction Path
Consider the following reaction mechanism
Step 1: ICl + H2 → HI + HCl
(slow)
Step 2: ICl + HI → HCl + I2
(fast)
The Species HCl is a
41
A.
B.
C.
D.
9.
Product
Catalyst
Reactant
Reaction Intermediate
Consider the following reaction mechanism
Step 1:
Cl(g) + O3(g) → ClO(g) + O2(g)
Step 2:
O(g) + ClO(g) → Cl(g) + O2(g)
The Reaction intermediate is
A.
B.
C.
D.
10.
Cl
O2
O3
ClO
In a reaction mechanism, the rate determining step is the
A.
B.
C.
D.
Fastest and has the lowest reaction rate.
Fastest and has the highest activation energy
Slowest and has the lowest activation energy
Slowest and has the highest activation energy
PE
Reaction Progress
11.
Select the true statement concerning the above potential energy diagram.
A.
B.
C.
D.
The catalyzed reaction has a larger ∆H
The uncatalyzed reaction has a larger ∆H
The catalyzed reaction has a greater rate of reaction
The uncatalyzed reaction has a greater rate of reaction
42
I
II
12.
O2
O3
NO
NO2
Consider the following reaction mechanism
Step 1: N2O(g) → N2(g) + O(g)
Step 2: N2O(g) + O(g) → N2(g) + O2(g)
The reactant in the overall reaction is
A.
B.
C.
D.
15.
I
II
III
IV
Consider the following reaction
Step 1: NO(g) + O3(g) → NO2(g) + O2(g)
Step 2: O(g) + NO2(g) → NO(g) + O2(g)
The catalyst is
A.
B.
C.
D.
14.
IV
Which point on the diagram above represents the potential energy of the activated complex formed
in the uncatalyzed reaction?
A.
B.
C.
D.
13.
III
O
O2
N2
N2O
Consider the following reaction
O3(g) + NO(g) ----- > NO2(g) + O2(g)
NO2(g) + O(g) ------ > NO(g) + O2(g)
The product in the overall reaction is
A.
B.
C.
D.
O2
O3
NO
NO2
43
Kinetics
1.
Web Review
Define the following:
Activation energy,
Mechanism
Activated Complex
Successful collision
Catalyst
Reaction rate
Enthalpy
Intermediate
Homogeneous reaction
Rate determining step
Heterogeneous reaction.
2.
3.
Na2CO3(aq) + 2HCl(aq) → CO2(g) + 2NaCl(aq) +H2O(l)
a)
Give four ways to increase the rate of the reaction.
b)
Give three properties that you could measure in order to determine the rate experiment.
Zn(s) + 2HCl(aq) → H2(g) + ZnCl2(aq)
44
a)
Give five specific ways to increase the rate.
4.
In low light, H2 and Cl2 do not react at all. When exposed to UV light, they react explosively!
Explain using the collision theory.
5.
A mixture of KClO3 and C12H12O11 do not react at all at room temperature. A drop of H2SO4 starts
the reaction, slowly at first, then it quickens into a flaming inferno. Explain using the collision
theory.
6.
Water puts out a fire. Explain using the collision theory.
7.
A glowing splint re-ignites in pure O2. Explain using the collision theory.
8.
Enzymes in the human body allow the oxidation of carbohydrates at 37 degrees Celsius.
9.
Draw an exothermic PE diagram. Include a catalyst. Label the change in enthalpy, the forward and
reverse activation energies and the activated complex.
45
10.
Repeat the above for an endothermic reaction.
11.
A student reacts CaCO3(aq) with excess HCl in an open container at a constant temperature. The
equation for the reaction is:
CaCO3(s) + 2HCl(aq) → CO2(g) + CaCl2(aq) + H2O(l)
In terms of the collision theory, describe what will happen to the rate of the reaction as the
reaction proceeds from the beginning to completion. Hint: what happens to the [HCl] as the
reaction proceeds and what effect would that have on the rate.
12.
A + WY
→
AWY
Fast
AWY + HA
→
A2WY + H
Slow
A3 + WY + H
Fast
A2WY + HA →
For the above reaction mechanism list the following:
a)
The overall equation
b)
A catalyst
c)
Intermediates
d)
Reactants
46
e)
Products
Describe how each change affects the rate.
13.
a)
Increasing the concentration of A
b)
Increasing the concentration of H
c)
Increasing the concentration of HA
d)
Removing WY completely
e)
Decreasing the temperature
Describe the KE and PE changes as two molecules:
a)
Approach to collide,
b)
Form an activated complex, and
c)
Form products in an exothermic reaction.
14.
Draw the PE diagram for a mechanism with three steps. How many activated complexes are there?
How many intermediates are there?
15.
Describe as endothermic or exothermic.
a)
2H2 + O2 → 2H2O + 300kJ
b)
NH4NO3(s) → NH4NO3(aq)
ΔH = +150kJ
16.
Change each equation in 15 from standard to ΔH notation or vice-versa.
17.
Which reaction at room temperature is faster and why?
a) Pb2+ + 2Cl- →
b) 2H2 + O2
→
PbCl2
or
2H2O
18.
List three commercial catalysts (they are in your textbook)
19.
Calculate the rate in moles/s.
Moles H2
10.0
15.0
21.0
24.0
Time (seconds)
200
300
400
500
47
20.
Indicate how each change will affect the rate of the reaction and the PE diagram and explain with
the collision theory.
a)
Increasing the temperature
b)
Increasing the concentration of a reactant
c)
Increasing the concentration of a product
b)
Addition of a catalyst
X + Y → XY
21.
slow
XY + Z → XYZ
fast
XYZ + W → XYW + Z
fast
a)
Identify intermediates, the catalyst and the rate-determining step.
b)
If the concentration of X was increased will the rate increase?
22.
You can only increase the surface area of a substance if it is in certain physical state. What is it?
23.
Two solid reactants react. Is it a homogeneous or heterogeneous reaction?
24.
What is the mathematical relationship between each of the following?
Reaction rate and activation energy
Reaction rate and reactant concentration
Reaction rate and temperature
25.
Draw a collision energy distribution diagram for a reaction where the y axis is fraction of
collisions and the x axis is collision energy. Draw the Ea line showing about 10% of the collisions
having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient
energy.
48
Faction of
collisions
Collision Energy
26.
Shade in the area of the collision energy distribution diagram showing those collisions that do not
have the required energy to be successful at the temperature below.
Faction of
collisions
Collision Energy
49
Practice Test # 1
1.
2.
Consider the following reaction mechanism:
step 1:
M
+
X
→
step 2:
MX +
A
→
The chemical species MX is a(n)
A.
catalyst
B.
inhibitor
C.
final product
D.
reaction intermediate
1.0
1.3
2.5
5.0
A.
B.
C.
D.
x
x
x
x
10-5 mol/s
10-6 mol/s
10-6 mol/s
10-6 mol/s
nature of the reactants
presence of a catalyst
temperature of system
concentration of reactants
I and IV only
II and III only
II, III, and IV only
I, II, III, and IV
Which of the following equations represents an endothermic reaction?
A.
B.
C.
D.
5.
X
Which of the following factors affect the rates of both homogeneous and heterogeneous reactions.
I
II
III
IV
4.
+
Consider the following reaction:
2N2O5(g) → 4NO2(g) + O2(g)
At a certain temperature the rate of decomposition of N2O5(g) is 2.5 x 10-6 mol/s. The rate of
formation of NO2 is
A.
B.
C.
D.
3.
MX
D
N2O4(g)
2H2(g)
2BrCl(g)
2H2(g)
+ 59 kJ → 2NO2(g)
+ O2(g) → 2H2O(l) + 572 kJ
-29.3 kJ →Br2(g) + Cl2(g)
+ O2(g) → 2H2O(l)
ΔH
= -572 kJ
Consider the potential energy diagram. The activation energy for the reverse reaction is
50
PE
(kJ)
170kJ
30kJ
Progress of the reaction
A.
B.
C.
D.
6.
Consider the following mechanism: Step 1:
Step 2:
The reaction intermediate is
A.
B.
C.
D.
7.
+ O2
+ O2
Cl
O2
O3
ClO
fastest and has the lowest activation rate.
fastest and has the highest activation rate.
slowest and has the lowest activation rate.
slowest and has the highest activation rate.
A catalyst increases the rate of a reaction by
A.
B.
C.
D.
9.
Cl + O3 → ClO
O + ClO → Cl
In a reaction mechanism, the rate determining step is the
A.
B.
C.
D.
8.
30 kJ
140 kJ
170 kJ
200 kJ
increasing the concentration of reactant(s).
decreasing the concentration of the reactant(s).
increasing the activation energy of the overall reaction.
decreasing the activation energy of the overall reaction.
Which of the following properties could be used to measure the rate of the following reaction in a
open container. Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
A.
B.
C.
D.
mass of Zn
solubility of HCl
concentration of Clcolour of the solution
51
10.
Consider the following potential energy diagram:
PE
(kJ)
Progress of the reaction
The above diagram represents an
A.
B.
C.
D.
11.
exothermic reaction involving one step.
exothermic reaction involving two steps.
endothermic reaction involving one step.
endothermic reaction involving two steps.
Which of the following are necessary for successful collisions to occur?
I.
II.
III.
A.
B.
C.
D.
12.
Favourable geometry
Sufficient energy
Large ΔH
I only
I and II only
II and III only
I, II, and III
Consider the following reaction:
2H2O2(aq) →
2H2O(l) + O2(g)
When 1.0 g of KI is added to the H2O2, bubbles of O2 are produced at an increased rate, The KI is
a
A.
B.
C.
D.
product
catalyst
reactant
intermediate
52
13.
Consider the following
I.
Frequency of successful collision
II.
Volume of the reaction vessel
III.
Pressure of the system
IV
Mass of the system
To increase the rate of a chemical reaction there must be an increase in
A.
B.
C.
D.
14.
I only
I and III only
I, III and IV only
I, II, III, and IV
Consider the following reaction mechanism:
Step1: ICl + H2 → HI + HCl slow
Step 2: ICl + HI → HCl + I2 fast
The species HCl is a
A.
B.
C.
D.
15.
product
catalyst
reactant
reaction intermediate
Consider the following potential energy diagram:
125
PE
(kJ)
100
50
25
Progress of the reaction
53
The activation energy in the forward direction is
A.
B.
C.
D.
16.
Consider the following reactions:
I.
N2 + O2(g) → 2NO(g)
II.
Mg(s) + O2(g) → 2MgO(s)
III.
CaCO3(s) + 2H+(aq) → Ca2+ (aq) + H2O(l) + CO2(g)
Increasing the surface area will increase the reaction rate in
A.
B.
C.
D.
17.
25 kJ
50 kJ
100 kJ
125 kJ
II only
I and III only
II and III only
I, II, and III
Consider the following reaction mechanism:
Step 1: V3+ + Cu2+ → V4+ + Cu+
Step 2: Cu+ + Fe3+→ Cu2+ + Fe2+ slow
The reaction intermediate is
A.
B.
C.
D.
18.
The rate of a chemical reaction can be expressed in
A.
B.
C.
D.
19.
grams per mole
energy consumed per mole
volume of gas per unit time
mole formed per litre of solution
Consider the following reaction:
2MnO4-(aq) + 5C2O42-(aq) 16H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l)
The rate of decomposition of the oxalate ion is increased by
A.
B.
C.
D.
20.
Cu+
Cu2+
V3+
Fe3+
adding NaOH.
removing CO2
adding a catalyst
decreasing the pressure
The minimum amount of energy needed to start a reaction is called the
54
A.
B.
C.
D.
21.
An 8.00 g piece of magnesium was placed into 6.0 M HCl. After 25 s, 3.50 g of unreacted
magnesium remained. The average rate at which magnesium was consumed is
A.
B.
C.
D.
22.
0.14 g/s
0.18 g/s
0.32 g/s
4.50 g/s
In general rates double when the temperature is increased by 10 oC. The temperature of a reaction
is increased by 40 oC. The rate will increase by a factor of
A.
B.
C.
D.
23.
activation energy.
energy of reaction.
entropy of reaction
reaction mechanism energy
2
4
8
16
Consider the following factors
I.
reactant particles collide
II.
sufficient kinetic energy is present
III.
a favourable geometry exists
IV.
catalysts are present
Which combination of the above factors is required for all successful collisions?
A.
B.
C.
D.
24.
Consider the following reaction at constant temperature in an open system:
MgCO3(s) + 2HCl(aq) → CO2(g) + H2O(l) + MgCl2(aq)
Which of the following properties could be used to determine the reaction rate.
A.
B.
C.
D.
25.
I only
II and III only
I, II and III only
I, II, III, and IV
mass of the system
pressure of the gas
concentration of H2O
concentration of MgCO3
Which combination of factors will affect the rate of the following reaction?
MgCO3(s) + 2HCl(aq) → CO2(g) + H2O(l) + MgCl2(aq)
A.
temperature and surface area only
B.
temperature and concentration only
C.
concentration and surface area only
D.
temperature, concentration, and surface area only
55
26.
As reactant molecules approach each other
A.
B.
C.
D.
heat is released
a reaction intermediate forms
kinetic energy changes into potential energy
potential energy changes into kinetic energy
Consider the following potential energy diagram for the next five questions.
2
PE
4
1
3
Progress of reaction
27.
The interval representing ΔH for the reverse reaction is
A.
B.
C.
D.
28.
The interval representing ΔH for the forward reaction is
A.
B.
C.
D.
29.
1
2
3
4
The interval representing Ea for the forward reaction is
A.
B.
C.
D.
31.
1
2
3
4
The interval representing Ea for the reverse reaction is
A.
B.
C.
D.
30.
1
2
3
4
1
2
3
4
The interval representing the energy of the activated complex is
56
A.
B.
C.
D.
32.
When a catalyst is added to a reaction, ΔH will
A.
B.
C.
D.
33.
1
2
3
4
increase slowly
remain constant
decrease slowly
increase rapidly due to the alternate pathway
Consider the following reaction: Zn(s) + 2HCl(aq) → H2(g) + ZnCl2(aq)
Data for the reaction is shown below:
Time
0
2
4
Mass of Zn (g)
Volume of H2 (mL)
Temperature (oC)
4.65
4.50
4.35
0
50
100
20
21
22
The rate of the reaction can be measured in units of
A.
B.
C.
D.
34.
When a lit match is touched to the wick of a candle, the candle begins to burn. When the match is
removed, the candle continues to burn, the match,
A.
B.
C.
D.
35.
behaves as a catalyst
supplies the activation energy
is part of the rate determining step
lowers the activation energy barrier
Consider the following reaction: 2NO(g) + O2(g) → 2NO2(g) + 112 kJ
ΔH for the above reaction is:
A.
B.
C.
D.
36.
g/min
g/mL
min/mL
g/(mL)(oC)
positive and the reaction is exothermic
negative and the reaction is exothermic
positive and the reaction is endothermic
negative and the reaction is endothermic
Consider the following reaction: 2S(s) + 3O2(g) → 2SO2(g) + heat
The rate of this reaction could be increased by
57
A.
B.
C.
D.
37.
Consider the following reaction: ½H2 + ½I2 → HI ΔH = +28 kJ
The activation energy for the formation of HI is 167 kJ. The activation energy for the
decomposition of HI is
A.
B.
C.
D.
38.
A.
decreasing the temperature
adding a catalyst
increasing the concentration of S
decreasing the surface area of the S
28 kJ
139 kJ
167 kJ
195 kJ
Some reactants are more reactive than others because of their activation energy Ea. What graph
shows the relationship between Ea and rate.
B.
Ea
Ea
Rate
C.
Rate
D.
Ea
Rate
39.
Rate
The activated complex is a chemical species that is
A.
B.
C.
D.
40.
Ea
stable and has low PE.
stable and has high PE.
unstable and has low PE.
unstable and has high PE.
As an activated complex changes into products,
A.
B.
C.
D.
potential energy changes into kinetic energy.
kinetic energy changes into potential energy.
kinetic energy changes into activation energy.
potential energy changes into activation energy.
58
Subjective
PE
Progress of the reaction
1.
On the potential energy diagram above, clearly label the activation energy, heat of the reaction
(∆H), and the energy of the activated complex.
2.
Is the above reaction endothermic or exothermic in the forward direction?
3.
On the graph below, draw the potential energy diagram for an exothermic reaction and label the
activation energy.
PE
Progress of the reaction
4.
a)
Nitric oxide (NO) is involved in the decomposition of ozone by the following mechanism:
Step 1: O3 + sunlight → O2 + O
Step 2: O3 + NO → NO2 + O2
Step 3: NO2 + O → NO + O2
Write the net equation for the decomposition reaction
59
b)
Identify a catalyst
c)
Identify a reaction intermediate
d)
What is the function of sunlight in this reaction?
5.
Consider the following reaction:
a)
Explain why the reaction is likely to involve more than one step.
b)
A proposed mechanism for the above reaction is:
Step 1: NO + H2 → N + H2O
Step 2:
?
Step 3: N2O + H2 → N2 + H2O
2NO + 2H2 → 2H2O + N2
Write the equation for step 2.
6.
Define the term activation energy.
7.
The combustion of coal, C, produces carbon dioxide and water according to the following
equation: C(s) + O2(g) → CO2(g) + 394 kJ
a)
What is ∆H for this reaction?
b)
Using the collision theory, explain why a lump of coal does not react with oxygen at room
temperature and pressure.
c)
Many coalmine disasters have resulted when a spark ignites coal dust in the air. Explain using the
collision theory.
8.
State two reasons why some collisions may not result in a chemical reaction.
9.
A student wishes to monitor the rate of the following reaction:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
60
Identify two different properties that could be used to monitor the rate of the reaction. Describe
and explain the changes that would occur.
Property 1
Change and explanation
Property 2
Change and explanation
10.
An experiment is done to determine the rate of the following reaction:
2Al(s) + 6HCl(aq) → 3H2(g) + 2AlCl3(aq)
Balance
1.00 g of Al is placed in a beaker
and allowed to react for 12.00 minutes
with 2.00 M HCl. If the rate of consumption
of HCl is 0.250 g/min, calculate the amount
of Al remaining.
61
Kinetics Practice Test # 2
1.
Which of the following units could be used to express the reaction rate?
A.
B.
C.
D.
2.
Consider the reaction:
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
The rate of production of ZnCl2, can be increased by
A.
B.
C.
D.
3.
potential energy changes to kinetic energy.
kinetic energy changes to potential energy.
kinetic energy changes to activation energy.
potential energy changes to activation energy.
Which of the following is most likely to have the greatest rate at room temperature.
A.
B.
C.
D.
6
enthalpy.
activation energy.
the ΔH of the reaction.
the activated complex.
As an activated complex changes to products,
A.
B.
C
D.
5.
decreasing the [HCl].
increasing the temperature
increasing the volume of H2.
decreasing the surface area of Zn.
The statement, the minimum energy needed for a successful collision, defines
A.
B.
C.
D.
4.
mL/s
mL/g
g/mL
mL/mol
2H2(g) + O2(g) → 2H2O(l)
2Ag+(aq) + CrO42-(aq) → Ag2CrO4(s)
Pb(s) + 2HCl(aq) → PbCl2(aq) + H2(g)
CH4(g) + 2O2(g) → CO2(g) + H2O(g)
Consider the following PE diagram for an uncatalyzed and catalyzed reaction
62
PE
(kJ)
35kJ
10kJ
15kJ
Progress of the Reaction
Which of the following describes the forward catalyzed reaction?
Activation Energy (kJ)
A.
B.
C.
D.
7.
product
catalyst
reactant
intermediate
Activation energy can be described as the
A.
B.
C.
D.
9.
-15
15
-15
15
A substance that increases the rate of a reaction without appearing in the equation for the overall
reaction is a(an)
A.
B.
C.
D.
8.
10
10
25
25
ΔH (kJ)
energy of motion
energy of the activated complex.
energy difference between the reactants and the products.
energy difference between the reactants and the activated complex.
What effect does a catalyst have on a reaction?
A.
B.
C.
D.
It changes the ΔH of a reaction.
It increases the kinetic energy of the reactants.
It decreases the potential energy of the products.
It provides a reaction mechanism with a lower activation energy.
63
10.
Consider the following reaction involving 1.0 g of powdered zinc:
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
Trial
Temperature (0C)
Concentration of HCl
1
2
3
40
20
40
3.0
3.0
6.0
The rates in order of fastest to slowest are
A.
B.
C.
D.
11.
1, 2, 3
2, 1, 3
3, 1, 2
3, 2, 1
Consider the following potential energy diagram for a reversible reaction:
140
130
PE (kJ)
110
Progress of the reaction
Which of the following describes the system above?
A.
B.
C.
D.
12.
Activation Energy (kJ)
ΔH (kJ)
reverse
reverse
forward
forward
10
10
30
20
-20
-30
+10
+30
An activated complex is a chemical species that is
A.
B.
C.
D.
13.
Reaction
stable and has low PE.
stable and has high PE.
unstable and has low PE.
unstable and has high PE.
Consider the reaction: Ca(s) + 2H2O(l) →
Ca(OH)2(aq) + H2(g)
64
At a certain temperature, 2.05 g Ca reacts completely in 30.0 seconds. The rate of consumption of
Ca is
A.
B.
C.
D.
14.
15.
0.00208 mol/min
0.0833 mol/min
0.102 mol/min
5.00 mol/min
Increasing the temperature of a reaction increases the reaction rate by
I.
II.
III.
increasing frequency of collision
increasing the kinetic energy of collision
decreasing the potential energy of the collision
A.
B.
C.
D.
I only.
I and II only.
II and III only.
I, II, and III.
A certain reaction is able to proceed by various mechanisms. Each mechanism has a different Ea
and results in a different overall rate. Which of the following best describes the relationship
between the Ea values and the rates?
A.
B.
Ea
Ea
Rate
C.
Rate
D.
Ea
Rate
Ea
Rate
65
16.
For collisions to be successful, reactants must have
A.
B
C.
D.
17.
favourable geometry.
sufficient heat of reaction only.
sufficient potential energy only.
sufficient kinetic energy and favourable geometry.
Consider the following reaction: 1/2 H2(g) + 1/2 I2(g) → HI(g)
ΔH = +28 kJ
The activation energy for the formation of HI is 167 kJ. The activation energy for the
decomposition of HI is
A.
B.
C.
D.
18.
28 kJ
139 kJ
167 kJ
195 kJ
Which of the following factors affects the rate of heterogeneous reactions only?
A.
B.
C.
D.
nature of the reactant
temperature
surface area of reactants
concentration of reactants
19.
A 25.0 mL sample of hydrogen peroxide decomposes producing 50.0 mL of oxygen gas in 137 s.
The rate of formation of O2 in mL/min is
A.
B.
C.
D.
20.
0.182 mL/min
0.365 mL/min
10.9 mL/min
21.9 mL/min
Consider the following reaction mechanism:
step 1
step 2
2NO + H2 → N2 + H2O2
H2O2 + H2 → 2H2O
In this reaction H2 is a
A.
B.
C.
D.
product
catalyst
reactant
reaction intermediate
66
21.
Which of the following properties could be used to measure the rate of the following reaction
taking place in an open container?
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
A.
B.
C.
D.
22.
mass of Zn
solubility of HCl
concentration of Clcolour of the solution
Consider the following reaction: N2 + 3H2 → 2NH3
The rate of formation of NH3 is 3.0 mole/min. The rate of consumption of H2 is:
A.
B.
C.
D.
23.
1.5 mole/min
2.0 mole/min
4.5 mole/min
9.0 mole/min
Consider the following reaction mechanism:
NO2 + NO2 → N2O4
N2O4 + CO → CO2 + NO + NO2
Step 1
Step 2
In the overall reaction, N2O4 is a
A.
B.
C.
D.
24.
product
catalyst
reactant
reaction intermediate
Consider the following mechanism:
NO + O3 → NO2 + O2
O + NO2 → NO + O2
Step 1
Step 2
The catalyst is
A.
B.
C.
D.
O2
O3
NO
NO2
67
25.
Consider the following reaction: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
The rate of this reaction increases when more Mg is added. This change is caused by the
A.
B.
C.
D.
26.
addition of a catalyst
increase in surface area
change in the nature of the reactants
increase in concentration of reactants
Consider the following PE diagram
100
PE (kJ)
40
20
Progress of the reaction
The forward reaction can be described as
A.
B.
C.
D.
27.
ΔH
Ea
Type
+20
+20
-20
-20
80
60
80
100
endothermic
exothermic
exothermic
endothermic
Consider the following reaction: HgO(s) → Hg(l) + 1/2O2(g)
The rate of this reaction can be expressed as
A.
B.
C.
D.
rate
rate
rate
rate
=
=
=
=
[O2]1/2
Δ[O2]/Δt
Δ[Hg]/Δt
Δ[HgO]/Δt
68
28.
Which of the following would react most rapidly?
A.
B.
C.
D.
29.
Addition of a catalyst to a reaction increases the rate because it
A.
B.
C.
D.
30.
Powdered Zn in 1.0 M HCl at 25 0C
Powdered Zn in 2.0 M HCl at 40 0C
A lump of Zn in 2.0 M HCl at 25 0C
A lump of Zn in 1.0 M HCl at 40 0C
increases the value of ΔH
decreases the value of ΔH
provides an alternate mechanism with a lower Ea
provides an alternate mechanism with a higher Ea
When a collision occurs between two reactant species which possess between them the
minimum kinetic energy a product does not always form. This may be a result of
A.
B.
C.
D.
low temperature
small surface area
low concentrations
unfavourable geometry
Subjective Section
1.
An experiment is done to determine the rate of the following reaction;
2Al(s) + 6HCl(aq) → 3H2(g) + 2AlCl3(aq)
H2
The following data are collected:
Time (s)
Mass of Beaker + Contents (g)
270.170 g
0.0
30.0
60.0
270.230
270.200
270.170
Calculate the rate of consumption of Al in moles/min
2.
3.
Define the term activation energy.
Define the word Activated complex.
4.
Define the word mechanism.
69
5.
Consider the following reaction mechanism
Step 1
6.
?
Step 2
H2 + Cl → HCl + H
Step 3
H + Cl2 → HCl + Cl
Step 4
Cl + Cl → Cl2
Overall
H2 + Cl2 → 2HCl
a)
Write the equation for step 1
b)
Identify the reaction intermediate(s)
Consider the overall reaction: 4HBr + O2 → 2H2O + 2Br2
A proposed three-step mechanism is:
Step 1
HBr + O2 → HOOBr
Step 2
?
Step 3
HBr + HOBr → H2O + Br2
Write the equation for step 2.
7.
A student wishes to monitor the rate of the following reaction:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
Identify two properties that could be used to monitor the rate of the reaction. Describe and explain
the changes that would occur.
Property 1
Change and explanation
70
Property 2
Change and explanation
8.
Carbon burns in air according to the following equation:
C(s) + O2(g) → CO2(g)
List four ways the rate of the above reaction could be increased.
9.
Sketch the potential energy diagram for an endothermic reaction in the space below. On your
diagram clearly label:
PE
Progress of the Reaction
i)
ii)
iii)
the energy of the activated complex
the activation energy
ΔH
71
Kinetics Worksheets
for
Chemistry 12
Mr. Iannone
Notes- double click on the lesson number and download Power Point Viewer if you do not have it.
Worksheets
Quiz
Q1
Q2
Q3
Q4
Q5
1
2
3
4
5
Monitoring Reaction Rates
Factors that Change the Rate
Collision Theory
PE Diagrams
Mechanisms
WS 1
WS 2
WS 3
WS 4
WS5
6
7
Lab: The Iodine Clock Reaction
Review
8.
9.
Review
Test
Web Review
Practice Test 1
Practice Test 2
Quizmebc
Text book
Hebden
Read Unit I
The following workbook is designed to ensure that you can demonstrate your understanding of all
aspects of the kinetics unit. The minimum expectation is that you do all of these questions by the due
dates given by your teacher. Do the questions. Use your notes from class to assist you. Then after you
have finished go to the web site to evaluate your work. Make a list of those things that you don’t quite
understand and bring them to class. I will go over them as best as I can. There are other things that you
should do to prepare for the test at the end of the unit. Remember, what you put into this course is what
you will get out. There is no substitute for consistent effort and hard work. If you can’t do a question, get
some help before the end of the unit, you need to know, understand, and remember everything. Good
luck! I know you can do well in this unit. Web Site Address: sd34.bc.ca/schools/wjm/science/chem12
Ws #1
Monitoring and Calculating Reaction Rates
1. Read unit 1 of Hebden over the next week. “A” students should read it twice.
2. a) When measuring a property associated with a reactant in a reaction, does it increase or decrease?
Decrease as reactants are converted into products
72
2. b) When measuring a property associated with a product in a reaction, does it increase or decrease?
Increase as reactants are converted into products
3. Give three ways to measure the rate of the following reaction. State the specific properties that you
would monitor and include units (amount is not a specific property). State if each property would increase
or decrease. Describe in each case how you would calculate the reaction rate.
2HNO3(aq)
+ Cu(s) → NO2(g) +H2O(l) + CuNO3(aq)
The first one is done for you.
i)
Mass of Cu
mass/time
ii)
[HNO3]
M/time
iii)
Volume of NO2
L/time
iv)
[CuNO3]
M/time
v)
Mass of open container
mass/time
vi)
Pressure of closed container
Pressure/time
Grams
Decrease
Rate =
M
Decrease
Rate =
L
Increase
Rate =
M
increase
Rate =
Grams
Decrease
Rate =
KPa
Increase
Rate =
Any three of the above answers are fine.
Mass of copper (g)
Time (min)
3.26
5.0
2.93
7.0
2.61
9.0
4. Calculate the rate in units of (g Cu/min).
3.26 - 2.61 g Cu = 0.16g/min
9.0 - 5.0 min
5. Calculate the rate in units of (mole Cu/min).
0. 16g Cu x
1 mol = 0.0026 mol/min
min
63.5 g
6. Calculate the rate in moles HNO3 consumed per second (remember that 2 moles are consumed per 1
mole of Cu).
0.0026 mol Cu
x 1 min x
2 moles HNO3 = 8.5 x 10-5 moles/s
min
60s
1 mole Cu
7. Calculate the rate in units of (g/sec) for HNO3.
8.5 x 10-5 moles HNO3 x 63.0 g
= 0.0054 g/s
s
1 mole
Volume of NO2 (mL)
10.0
11.5
12.7
73
Time (sec)
0.00
5.00
10.00
8. Calculate the rate in units of (mL NO2/sec).
Rate = 12.7 - 10.0 ml = 0.27 ml/s
10.00 - 0.00 s
9. Calculate the rate in units of (L NO2/min).
0.27 ml x 60s x 1L
= 0.016 L/min
s
1 min 1000 ml
10. Calculate the rate in units of (moles NO2/min) at STP.
0.0162 L x 1 mol = 7.2 x 10-4 mol/min
min
22.4 L
11. Calculate the rate in units of (moles HNO3/min) at STP (remember that 2 moles are consumed per 1
mole of NO2)
7.23 x 10-4 mol NO2 x 2 moles HNO3 = 0.0015 moles/min
min
1 mole NO2
12. Calculate the rate of the following reaction:
2NO (g) +
2H2 (g)
→
N2 (g) + 2H2O (g)
moles
NO
Time(s)
0.080
0.060
0.040
0.020
0.0 2.0 4.0 6.0 8.0 10.0 11.0 12.0
74
Rate
=
(0.080 – 0.020) moles
=
0.0060 moles/s
(12.0 – 2.0) s
a) What is the rate in moles NO per second?
0.0060 moles/s
b) What is the rate in moles N2 per second?
0.0030 moles/s
c) What is the rate in grams NO per min?
11 g/min
d) What is the rate in grams N2 per hour?
3.0 x 102g/h
13. Choose three properties that you could measure in order to monitor the rate of the following reaction.
Cu (s) + 2AgNO3 (aq) → 2 Ag (s) + Cu(NO3)2 (aq)
Property
Unit of Measurement
Change
1.
Mass Cu
grams
decrease
2.
Mass Ag
grams
increase
3.
Intensity [Cu+2]
M
increase
14. Calculate the rate of the following reaction in units of M/s:
Zn (s) + 2HCL (aq) → ZnCl2 (aq)
Molarity of HCL (M)
time (seconds)
0.612
21.0
Rate = (1.05 - 0.612) M
(29.0 - 21.0) s
=
+
H2 (g)
0.813
25.0
1.05
29.0
0.055 M/s
15. Calculate the rate of the following reaction in L/min:
Zn (s) + 2HCL (aq) → ZnCl2 (aq)
+
H2 (g)
Volume of H2 (L)
0.255
0.550
0.790
time (minutes)
1.0
2.0
3.0
75
Rate = (0.790 - 0.255) M
(3.0 - 1.0) s
=
0.27 L/min
16. If 0.369g of HCl is neutralized with 0.250M NaOH in 25.0 seconds, what is the reaction rate in moles
HCL /min.
Rate =
WS # 2
0.369g x 1 mole
36.5g
0.41666 min
= 0.0243 mole/min
Factors That Change The Reaction Rate
Homogeneous reactions
- reactants are in the same phase (aq), (g) , or (l) and are thoroughly mixed.
Heterogeneous reactions
- reactants are in the two or more phases and are not thoroughly mixed (two solids do not mix).
Classify as Homogeneous or Heterogeneous:
1.
Zn (s) + 2 HCl (aq)
→
H2 (g) + ZnCl2
2.
Ag+ (aq) + Cl- (aq)
→
AgCl
3.
H2 (g) + F2 (g)
4.
2Al (s) + 3I2 (s)
→
→
(s)
(aq)
heterogeneous
homogeneous
2HF (g)
homogeneous
2AlI3
heterogeneous
(s)
The following four factors will increase the rate of a chemical reaction that is homogeneous:
1.
Increasing the temperature.
2.
3.
4.
5.
Increasing the reactant concentration.
Adding a catalyst
Changing the nature of the reaction.
Increasing the pressure for gases
The above four factors as well as the two below will increase the rate of a heterogeneous reaction:
6.
7.
Increasing the surface area of a solid.
Agitation
76
Which factor will only increase the rate of a gaseous reaction?
8.
Pressure
For each reaction specifically describe all of the ways to increase the reaction rate
(i.e.. increase[H2]).
1.
H2 (g) + F2 (g) → 2 HF (g)
This reaction is homogeneous so the first four factors will work.
Increasing the temperature
Increasing the pressure
Increasing [H2] or [F2]
Adding a catalyst
2.
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O
factors will work.
(l)
This reaction is homogeneous so the first four
(aq)
This reaction is heterogeneous most of the factors
Increasing the temperature
Increasing [HCl] or [NaOH]
Adding a catalyst
3.
Zn (s) + 2 HCl (aq)
→ H2 (g) + ZnCl2
will work, except pressure- need a gaseous
reactant..
Increasing the temperature
Increasing [HCl]
Adding a catalyst
Increasing the surface area of Zn(s)
Agitation
4.
State three examples of chemical reactions that are desired to be slow.
Food spoiling
Metal corrosion
Erosion
5.
Give three examples of chemical reactions that are desired to be fast.
Combustion of gasoline in automobiles
Industrial chemical production
Cooking food
The combustion of gasoline in a car engine; while accelerating.
77
6.
List all of the ways to increase the rate of the following reaction:
H2O2 (aq) → H2 (g) + O2 (g)
Increasing the temperature
Increasing [H2O2]
Adding a catalyst
I. Homogeneous reactions are generally faster than heterogeneous- the reactants are mixed better and
therefore there are more collisions between reactant particles.
HCl (aq) + NaOH (aq) →
is
NaCl (aq) + H2O
(l)
faster than
→ H2 (g) + ZnCl2
Zn (s) + 2 HCl (aq)
(aq)
II. Simple ionic reactions (where there are no bonds to break) are generally faster than more complex
ionic reactions (where there are bonds to break).
Pb+2 (aq) + 2Cl- (aq)
is
2Na+ (aq) + 2ClO- (aq) →
→
PbCl2
(l)
faster than
2Na+ (aq) + 2Cl-(aq)
+ O2
(g)
1. Indicate the faster and slower reaction and explain why.
a) 2Al (s) + 3I2 (s)
→
2AlI3
(s)
Heterogeneous reaction with bonds to break will be slow.
b) Ag+(aq) + Cl-(aq)
→
AgCl (s)
Homogeneous reaction with no bonds to break will be fast.
2. Indicate the faster and slower reaction and explain why.
a) 2Al (s) + 3I2 (s)
→
2AlI3
(s)
Slow. The reaction is heterogeneous (two solid do not mix) with bonds to break.
b) 2Na+ (aq) + 2ClO- (aq)
→
2Na+ (aq) + 2Cl-(aq)
+ O2
(g)
Faster. The reaction is homogeneous.
78
3. Indicate the faster and slower reaction and explain why.
a) 3Ba+2(aq) + 2PO4-3 (aq) →
Ba3(PO4)2(aq)
Faster. The reaction is homogeneous and simple ionic with no bonds to break.
b) Cu(s) + 2Ag+(aq) →
Cu+2 (aq) + 2Ag (s)
Slow. The reaction is heterogeneous and the Cu(s) bonds need to be broken.
Ws # 3 Collision Theory
1.
2.
Chemical reactions are the result of collisions between reactant particles, where bonds are broken
and new ones form.
A successful collision requires sufficient energy and favorable geometry.
3.
Describe as fast, medium or slow. Explain!
i) 2 H2 (g) + O2 (g)
→ 2 H20 (l) (room temperature)
Slow. Gas reactions are slower than aqueous.
ii) 2 Ag+ (aq) + CO32- (aq) → Ag2CO3
(s)
Fast. Homogeneous reaction simple ionic- there are no bonds to break
iii)
2 HCl (aq) + Na2CO3 (aq)
→
CO2 (g) + 2 NaCl (aq) + H20 (l)
Medium. Homogeneous complex reaction - there are bonds to break.
4.
i) Describe how you would measure the rate of the reaction :
Zn (s) + 2 HCl (aq)
→
ZnCl2 (aq) + H2 (g)
Measure the decrease in Zn mass.
Measure the increase in H2 gas volume.
Measure the mass of an open container which decreasing due H2 escaping.
ii) List four ways to increase the rate.
Increasing the temperature
Increasing [HCl]
79
Adding a catalyst
Increasing the surface area of Zn(s)
Agitation
5.
A 10 °C temperature increase frequently doubles the rate of a slow reaction because:
a) The temperature has doubled.
b) The PE of the colliding particle has doubled.
c) The KE of the colliding particle has doubled.
d) The fraction of particles with sufficient KE to react has doubled.
6.
Both collisions A and B have the same KE. Which collision is successful and explain why.
Before Collision
After Collision
A)
B)
Collision B was successful due to favourable geometry.
7.
Use the collision theory to explain how each factor increases the reaction rate.
i) Increasing temperature
ii) Increasing [reactants]
iii)
Increasing surface area (solid)
iv)
Agitation of a heterogeneous reaction
v) Adding a catalyst
v)
i)
ii)
iii)
more collisions and harder collisions
more collisions
more collisions
iv)
more collisions
lower Ea & low energy collisions are
successful
80
8.
Explain why collision A was successful while collision B was unsuccessful.
Before Collision
After Collision
A)
B)
Collision A was successful because it had sufficient energy. The geometry is the same for
both collisions.
Explain each of the following using the collision theory. You need to explain each statement.
9.


a candle is not burning at room temperature


a match lights the candle


the candle continues to burn
Exothermic


H2O2 decomposes slowly at 20o C
Ea is too high


KI is added and rapid decomposition begins
Catalyst- lowers Ea


The temperature increases


H2 and O2 in a balloon do not react
Ea is too high


A spark ignites the balloon
Provides Ea
Ea is too high
Provides Ea
10.
Exothermic
11.
81


An explosion results
Exothermic


CH4 and O2 in a balloon do not react
Ea is too high


A platinum gauze ignites the balloon
Catalyst lowers Ea


An explosion results
Exothermic
12.
13. N2(g) + O2(g)
→
2NO(g)
Even though there are more than four billion collisions per second between N and O the amount of
product after a year is too small to detect. Using the collision theory, give two reasons why this reaction
might be slow.
i)
Low Temperature
ii)
High Ea
14. Give two reasons why some collisions will not result in a chemical reaction.
i)
Insufficient energy
ii)
Poor geometry
15. Give five reasons that might account for the following reaction having a high rate.
Ca (s) + 2 HCl (aq) → CaCl2 (aq) + H2 (g)
i)
ii)
iii)
iv)
v)
High surface area of Ca
High concentration of HCl
High temperature
Agitation
Nature of the reactant
16. C(s) + O2(g) → CO2(g)
List four ways the rate of the reaction could be increased.
i)
ii)
iii)
iv)
Increase temperature
Increase [ O2 ]
Increase pressure
Increase SA of C
(add catalyst or agitate)
17. State the relationship between Activation energy and the rate of a reaction. Graph the relationship.
Inverse because decreasing the activation energy increases the rate.
82
Rate
Activation Energy
18. State the relationship between Temperature and the rate of a reaction. Graph the relationship.
Direct, because increasing the temperature increases the rate.
Rate
Temperature
19. State the relationship between Concentration and the rate of a reaction. Graph the relationship.
Direct, because increasing the concentration increases the rate.
83
Rate
20.
Give three examples of reactions that are desired to be slow.
a)
b)
c)
21.
food spoiling
corrosion of metal
the fading of the colour in paint
Give three examples of reactions that are desired to be fast.
a)
b)
c)
explosions
the combustion of gasoline in your car when you are passing someone on the freeway
the commercial production of chemicals
Molarity
22. List all of the ways to increase the rate of the reaction:
2 H2O2 (aq)
→ 2 H2O (l) + O2 (g)
Increase the H2O2 concentration
Increase the Temperature
Add KI catalyst
23. Describe how you would measure the rate of the reaction above. State the property you would
measure and describe how it changes. Draw a diagram to illustrate your answer.
12.56 g
Mass of an open container
Decreases
84
or
Volume of O2
See notes for diagram.
Pressure of O2 in a closed system.
24.
See notes for diagram.
Pick the fastest and the slowest reaction at 20 °C.
Slowest gases are slower than aqueous
CO2(g) + 2 NaCl(aq) + H2O(l)
Fastest- simple ionic or double replacement
a) H2(g) + I2(g) →
2 HI(g)
b) 2 HCl(aq) + Na2CO3(aq)
c) Hg2+(aq) + 2 I -(aq)
→
→
HgI2(s)
25. H2 and O2 can exist at 20 °C for years without reacting. But when a small spark ignites the mixture it
reacts explosively. Explain using the Collision Theory.
The activation energy is too high at room temperature so there are no successful collisions.
A spark provides the kinetic energy required to overcome the Ea.
Exothermic reactions produce energy.
26.
Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of
collisions and the x-axis is collision energy. Draw the Ea line showing about 10% of the collisions
having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient
energy.
85
Ea (cat)
Faction of
collisions
Ea
Collision Energy
27.
Shade in the area of the collision energy distribution diagram showing those collisions that do not
have the required energy to be successful at the temperature below.
86
Ea
Faction of
collisions
Collision Energy
28.
Shade in the area of the collision energy distribution diagram showing those collisions that do
have the required energy to be successful at the temperature below. Redraw the curve at a higher
temperature.
Faction of
collisions
Ea
Higher
Temperature
87
Collision Energy
Kinetics - Descriptions
Use the collision theory to explain the following. Each sentence must be explained with a statement from
the collision theory.
1. An unlit candle does not burn. It burns after being lit with a match. It continues to burn.
Ea is too high.
Match is energy and provides Ea.
Exothermic
2. A solution is reacting very slowly to produce bubbles. KI is added and although it is not consumed in
the reaction , it speeds up the reaction rate. The temperature increases. The rate increases even more.
Ea is high
KI is a catalyst and lowers Ea and more collision are successful.
Exothermic→ temperature increases → rate increases
3. Iron reacts slowly with HCl. Iron is replaced with Zn and a much more vigorous reaction rate occurs.
Nature of reactant
Fe
→
high Ea
Zn
→
low Ea
4. H2 and O2 can exist together for years at room temperature without reacting. A spark begins the
reaction. An explosion results.
High Ea → collisions are not successful
88
A spark provides the Ea
Exothermic → explosion
5. Dilute nitric acid shows little reaction with copper. Concentrated nitric acid vigorously reacts.
Low concentration → few collisions
High concentration → many collisions
6. Water puts out a fire.
Lowers temperature so there are less collisions
The collisions have less energy.
7. Paint prevents rusting.
There are fewer collisions between reactant molecules.
8. A preservative in food slows rotting.
The preservative is an inhibitor; which increases the Ea.
Ws # 4
1.
Potential Energy Diagrams Worksheet
Draw the PE diagram showing the PE changes that occur during a successful collision of the
exothermic reaction:
H2
+
I2
→
2 HI + 250 KJ
The PE of the reactants = 400 KJ
The activation energy of the forward reaction = 200 KJ
600
kJ/mole
400
150
Reaction path
89
2.
Draw the PE diagram showing the PE changes that occur during a successful collision of the
endothermic reaction:
A + B + 200 KJ →
C
The PE of the reactants = 200 KJ
The Activation Energy in the forward direction = 250 KJ
450
KJ/mole
400
200
Reaction Path
90
3. Write the following reaction in ΔH notation.
A + B + 200 kJ →
A + B -----> C
C
ΔH= +200kJ
4. Write the following reaction in Standard Notation.
+
I2
→
H2 +
I2
→
H2
2 HI
ΔH = -250 kJ
2HI + 250 kJ
5. Write in Standard Notation.
2NI3 + 3BaCl2 →
2NI3
2NCl3
+ 3BaI2
+ 3BaCl2 + 175 kJ →
ΔH = 175 kJ
2NCl3
+ 3BaI2
6. Write in ΔH notation.
2AlBr3 + 3BaF2
→
2AlBr3 + 3BaF2
2AlF3
+ 3BaBr2 + 276 kJ
→ 2AlF3 + 3BaBr2
ΔH= -267 kJ
Draw the potential energy diagram for the following reactions.
7.
Potential energy of reactants =
Potential Energy of activated complex =
Potential Energy of the products =
250 kJ
350 kJ
300 kJ
91
350
KJ/mole
300
250
Reaction
Path
a) How does the potential energy change as the reaction proceeds?
b) How does the kinetic energy change as the reaction proceeds?
c) Is the reaction exothermic or endothermic?
d) What is the value of ΔH?
Increases
Decreases
Endothermic
ΔH= +50kJ
If a catalyst was added, what would happen to the energies of the:
e) Reactants?
f) Products?
g) Activated Complex?
h) If a catalyst was added what would happen to the rate?
Draw the potential energy diagram for the following reactions.
Nothing
Nothing
Decrease
Increase
8.
Potential energy of reactants =
Activation Energy =
Potential Energy of the products =
350 kJ
100 kJ
250 kJ
92
450
PE
KJ/mol
350
250
Reaction
Path
a) How does the potential energy change as the reaction proceeds?
b) How does the kinetic energy change as the reaction proceeds?
c) Is the reaction exothermic or endothermic?
d) What is the value of ΔH?
Decreases
Increases
Exothermic
ΔH= -100kJ
If the concentration of the reactants was increased, what would happen to the energies of the:
e) Reactants?
f) Products?
g) Activated Complex?
h) What would happen to the rate?
Draw the potential energy diagram for the following reactions.
9.
Potential energy of reactants =
Potential Energy of activated complex =
ΔH =
Nothing
Nothing
Nothing
Increase
200 kJ
400 kJ
150 kJ
93
400
PE
KJ/mol
350
200
Reaction
Path
a) How does the potential energy change as the reaction proceeds?
b) How does the kinetic energy change as the reaction proceeds?
c) Is the reaction exothermic or endothermic?
d) What is the value of ΔH?
If the temperature was increased, what would happen to the energies of the:
e) Reactants?
f) Products?
g) Activated Complex?
h) What would happen to the rate?
10.
Potential energy of products =
Potential Energy of activated complex =
ΔH=
Increases
Decreases
Endothermic
ΔH= 150 kJ
Nothing
Nothing
Nothing
Increase
50 kJ
400 kJ
-50 kJ
94
40
PE
KJ/mol
100
50
Reaction Path
a) How does the potential energy change as the reaction proceeds?
b) How does the kinetic energy change as the reaction proceeds?
c) Is the reaction exothermic or endothermic?
d) What is the value of ΔH?
Decreases
Increases
Exothermic
ΔH= -50kJ
If the surface area of the reactants was increased, what would happen to the energies of the:
e) Reactants?
f) Products?
g) Activated Complex?
h) What would happen to the rate?
Nothing
Nothing
Nothing
Increase
11. What is the only thing, other than changing the reaction that will change the potential energy diagram?
Describe how it will effect the diagram and the rate.
Catalyst
Lowers Ea alloys more low energy collisions to be successful and increase the
rate.
95
12. Label each interval on the potential energy diagram.
a)
a
b
c
d
e
Ea (forward) (catalyzed)
PE
b)
Ea (reverse)(catalyzed)
c)
ΔH
d)
Ea (forward) (uncatalyzed)
Reaction
Path
e)
Ea (reverse) (uncatalyzed)
12. Label each interval on the potential energy diagram.
a
a)
b
c
d
e
Ea (forward) (uncatalyzed)
PE
Reaction Path
b)
Ea (forward) (catalyzed)
96
c)
ΔH
d)
Ea (reverse) (uncatalyzed)
e)
Ea (reverse) (catalyzed)
Ws # 5 Mechanisms
1.
i)
ii)
iii)
2.
i)
ii)
iii)
iv)
v)
OCl- + H2O
HOCl + IHOI + OHThe net chemical equation is:
The reaction intermediates are:
The catalyst is:
Br2
→
Br + OCl2
Br + Cl
→
→
→
HOCl + OHHOI + ClH2O + OI-
OCl- + I- + → Cl- +OIHOCl
HOI OHH2 O
2Br
→
→
BrOCl + Cl
BrCl
fast
slow
fast
The net chemical equation is:
Br2 + OCl2 → BrOCl
+ BrCl
The reaction intermediates are:
Cl & Br
The catalyst is:
None
The rate determining step is
2
If the concentration of Br2 is increased will the rate of the reaction increase? Explain your answer.
No because it is not in the rate determining step.
vi) If the concentration of OCl2 is increased will the rate of the reaction increase? Explain your answer.
Yes because, OCl2 is in the rate determining step.
3. The mechanism for the catalytic decomposition of formic acid is shown below.
97
step 1
HCOOH + H+
step 2
[HCOOHH]+
step 3
[HCO]+
→ [HCOOHH]+
→
→
[HCO]+
CO
+ HOH
+ H+
The potential energy diagram is:
PE
190
180
170
160
150
Reaction
Path
i) The catalyst is
H+
Crosses out
from left to right
ii) The rate determining step is
Two
Highest
Ea
98
iii) ΔH =
+10 kJ
From start to
40 kJ
Reactants to
30 kJ
Products to the
160 kJ
After one
end
iiv) The forward activation energy is
the highest point
iv) The reverse activation energy is
highest point
v) The enthalpy of [HCOOHH]+ is
hump
vi) Is the reaction exothermic or endothermic?
Endo
Uphill
vii) Which chemical formula has the greatest potential energy?
(HCO)+ + HOH
Highest
HCOOH + H+
Lowest
point on graph
viii) Which chemical formula has the greatest kinetic energy?
point on graph
ix) Does this reaction absorb or release kinetic energy?
Absorb because it is
endothermic (uphill)
4. Define and remember the following definitions.
mechanism
A sequence of steps that determines the overall reaction.
activation energy
The minimum energy required in a successful collision.
rate determining step The slowest step in a reaction mechanism.
catalyst
A substance that increases the rate of a chemical reaction by providing
a alternate mechanism with lower activation energy. reaction intermediate
A chemical species
produced in a reaction mechanism and then consumed in a later step.
99
endothermic
A reaction that absorbs energy
exothermic
A reaction that produces energy
activated complex
A unstable reaction intermediate with high potential energy and low kinetic
energy.
ΔH
The change in enthalpy or heat content for a reaction.
reaction rate
The change in a reactant or product per unit of time.
5. The catalyzed decomposition of acetaldehyde has an overall reaction of:
CH3CHO → CH4
+ CO . Determine step 2 of the reaction mechanism.
A proposed mechanism is:
step 1
CH3CHO
step 2
HI
+
I2 →
+
CH3I
CH3I + HI + CO
→ I2
+
CH4
This is the only step 2 that
will give the overall reaction below.
CH3CHO → CH4
overall
+ CO
6. The following reaction has an overall reaction of:
2Ce4+
+
Tl+
→
2Ce3+
+
Tl3+
Determine step 2 of the reaction mechanism.
A proposed mechanism is:
step 1
Ce4+
+
Mn+2
→
Ce3+
+
Mn3+
step 2
Ce4+
+
Mn3+ →
Ce3+
+
Mn4+
Tl3+
+
Mn2+
This is the only step 2
that will give the overall reaction below
step 3
Mn4+
+
Tl+
→
overall
2Ce4+
+
Tl+
→
2Ce3+
+
Tl3+
100
7. A reaction has a overall equation of: Br2 + OCl2 → BrOCl + BrCl . Determine step 3 of the
mechanism.
step 1
Br2 → 2Br
step 2
Br + OCl2 →
step 3
Br + Cl
BrOCl
+ Cl
→ BrCl
This is the only step 3
that will give the overall reaction below
overall
Br2 + OCl2 → BrOCl + BrCl
List two intermediates:
Br
Cl
8. Complete the following mechanism.
step 1
→
NO +
Pt
NOPt +
NO →
NOPt
needed for
next step
step 2
O2Pt
+
N2
O2Pt needed
for next step and N2 needed to be a product
step 3
O2Pt
→
O2
overall
2NO →
N2
+ Pt
+ O2
Identify the catalyst
Pt
Identify the two intermediates
right to left
NOPt
Crosses out from left to right
O2Pt
Crosses out from
9. Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of collisions and
the x axis is collision energy. Draw the Ea line showing about 10% of the collisions having sufficient
energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy.
101
Ea
cat
Ea
Fraction of
collisions
Collision Energy
10. Shade in the area of the collision energy distribution diagram showing those collisions that have the
required energy to be successful at the low temperature shown below. Draw the curve that represents the
distribution at a higher temperature with a different color. Shade in the area representing the successful
collisions at the higher temperature with a new color.
102
Fraction of
collisions
Ea
103