Download energy and rates practice test answers

NAME:
SCH 4U ENERGY AND RATES TEST A
KNOW
COMM
INQ
MC
TOTAL
13
8
24
4
50
PART ONE: KNOWLEDGE (15 marks)
MULTIPLE CHOICE (15 marks)
For each question below, chose the CAPITAL letter of the answer and place it in the table below.
1.
An endothermic reaction is one where
a. heat is transferred from the surroundings into a system
b. heat is transferred from a system into the surroundings
c. kinetic energy is transformed into potential energy
d. there is no transfer of heat
e. none of the above
2.
The molar heat of vaporization of water is 42 kJ/mol. How much energy is released by the
condensation of 3.0 g of water?
a. 0.88 kJ
d. 250 kJ
b. 7.0 kJ
e. 0.07 kJ
c. 130 kJ
3.
What is another way to write the following equation?
C2H6(g)  C2H2(g) + 2H2(g) ΔH = 3.2  102 kJ/mol
a.
b.
c.
d.
e.
4.
C2H6(g)  C2H6(g) + 2H2(g) + 3.2  102 kJ
C2H6(g) + 3.2  102 kJ  C2H2(g) + 2H2(g)
2H2(g) + C2H2(g) + 3.2  102 kJ  C2H6(g)
C2H6(g) – 3.2  102 kJ  C2H2(g) + 2H2(g)
none of the above
Which statement concerning the accompanying diagram is true?
a.
b.
c.
d.
e.
H is positive
the system is endothermic
the system releases heat to the surroundings
the heat content of the reactants is less than the heat content of the products
the enthalpy of the products is greater than the enthalpy of reactants
5.
For which one of the following substances is the standard enthalpy of formation, H°f, equal to
zero?
a. water [H2O(l)]
d. carbon dioxide [CO2(g)]
b. lead [Pb(s)]
e. tin [Sn(g)]
c. carbon dioxide [CO2(s)]
Use the following data to determine the ΔH of vaporization for silicon tetrachloride at its boiling
point.
6.
a. –30.6 kJ
b. +30.6 kJ
c. –609.6 kJ
7.
d. +609.6 kJ
e. +1249.8 kJ
The combustion of magnesium in air is very exothermic.
If the given two reactions and their heats of reaction were used to determine the heat of
combustion of magnesium the result would be
a. x + y
d. x – 2y
b. x – y
e. not enough information is given
c. 2x – y
8.
a.
b.
c.
d.
e.
9.
The following property can be measured to determine the rate of the reaction
change in mass
change in colour
change in volume
change in pressure
all of the above depending on the reaction
In the reaction, N2 (g) + 2 O2 (g)  NO2 (g), if the concentration changes from 0.45 mol/L to 1.00
mol/L in 2 minutes, what is the overall rate of production of nitrogen dioxide in the system?
a. 3.64 mol/(L·min)
d. 12.6 mol/(L·min)
b. 0.275 mol/(L·min)
e. 0.333 mol/(L·min)
c. 0.137 mol/(L·min)
10.
a.
b.
c.
d.
e.
The presence of a catalyst is thought to increase the rate of a reaction by
changing the products that are formed in the reaction
decreasing the enthalpy change of the reaction
increasing the enthalpy change of the reaction
decreasing the activation energy of the reaction
increasing the activation energy of the reaction
11.
a.
b.
c.
d.
e.
If for the reaction aX + bY  products, the rate law is determined to be , r= [X]1[Y]0then
the order of the reaction is 0
increasing the concentration of Y will have no effect on the rate
increasing the concentration of X will have no effect on the rate
increasing the concentration of Y will increase the rate of the reaction
there is no way to determine the value of k
12.
The amount of energy required for a reaction to begin is known as
a. enthalpy change
d. kinetic energy
b. reaction energy
e. potential energy
c. activation energy
13.
When a reaction is broken down into a number of elementary steps, this is known as a
a. reaction progression
d. reaction step
b. reaction mechanism
e. none of the above
c. reaction pattern
14.
Consider the above reaction mechanism. The rate-determining step of this reaction is
a.
b.
c.
d.
e.
elementary step 1
elementary step 2
elementary step 3
elementary steps 2 and 3
impossible to tell from this information
PART TWO: COMMUNICATION (8 marks)
1.
A reaction has a molar enthalpy of reaction of -45 kJ/mol and the activation energy for the
reverse reaction is 120 kJ/mol. Draw a potential energy diagram for the reaction. (4 marks).
2.
Using a diagram and the concept of kinetic energy, explain why an increase in temperature
increases the rate of a chemical reaction. (4 marks)
PART THREE: INQUIRY (24 marks
1.
Determine the amount of heat required to heat 1.50 L of water from 15 °C to the boiling point in a
1.20 kg iron pot. (3 marks)
q = mcwaterΔT + mcironΔT
= (1.50 kg)(4.18 kJ/kg°C)(100-15°C) + (1.20 kg)(0.45 kJ/kg°C)(100-15°C)
= 530 kJ + 46
= 576 kJ
2.
A)
Calculate the heat of combustion for pentane using HEATS OF FORMATION.
(4 marks)
C5H12(l) + 8 O2(g)  5 CO2(g) + 6 H2O(g)
ΔH= Σ Hf products - Σ Hf reactants
= [5 CO2(g) + 6 H2O(g)] – [C5H12(l) + 8 O2(g)]
= [5(-393.5 kJ/mol) + 6(-241.8 kJ/mol)] – [-173.5 kJ/mol+ 8(0)]
= (-1967.5- 1450.8 +173.5) kJ/mol
= -3244.8 kJ/mol
B)
Calculate the mass of pentane required to heat 250.0 g of ice at -6°C to 85°C. (7 marks)
qgained water = mciceΔT1 + mlf + mcliquid waterΔT2
= (250 g)(2.1J/g°C)(0-(-6) °C) + (250 g)(333 J/g) + (250 g)(4.18J/g°C)(85-0°C)
= 3150 J + 83 250 J + 88 825 J
= 175 kJ
qlost pentane = -qgained water
= - 175 kJ
n= q/ΔH
= -175 kJ/-3244.8 kJ/mol
= 0.054 mol
m=nMM = 0.054 mol(72.17 g/mol) = 3.9 g
2.
Calculate ΔH for the reaction : 3 N2H4 (l) + 4 ClF3 (g) 3 N2 (g) + 12 HF(g) + 2 Cl2 (g), using the
following data. (5 marks)
1) 2 ClF3 (g) + 2 NH3 (g)  N2 (g) + 6 HF(g) + Cl2 (g)
2)
N2H4 (l) + O2 (g)  N2 (g) + 2 H2O (l)
ΔH= -622 kJ
3)
4 NH3 (g) + 3 O2 (g)  2 N2 (g) + 6 H2O(l)
ΔH= -1530 kJ
2 x 1) 4 ClF3 (g) + 4 NH3 (g)  2 N2 (g) + 12 HF(g) + 2 Cl2 (g)
3 x 2) 3 N2H4 (l) + 3 O2 (g)  3 N2 (g) + 6 H2O (l)
R 3)
2 N2 (g) + 6 H2O(l) 4 NH3 (g) + 3 O2 (g)
3 N2H4 (l) + 4 ClF3 (g) 3 N2 (g) + 12 HF(g) + 2 Cl2 (g)
3.
ΔH= -1196 kJ
ΔH= -2392 kJ
ΔH= -1866 kJ
ΔH= 1530 kJ
ΔH= -2728 kJ
Given the experimental data below, determine the rate equation, including the value for k for the
following reaction. (5 marks)
3 A (aq) + 2 B (aq) + C (aq)  products
[B]
[C]
Rate (mol L-1 s-1)
0.400
0.100
0.200
1.50 x 10-3
0.400
0.100
0.400
3.00 x 10-3
1.600
0.100
0.200
1.50 x 10-3
0.400
0.500
0.200
3.75 x 10-2
[A]
For A compare 1 and 3; [A] x 4, rate x1, therefore 0 order for A
For B compare 1 and 4; [B] x 5, rate x5 = 52, therefore 2nd order for B
For C compare 1 and 2; [C] x 2, rate x2, therefore 1st order for C
r=k[B]2[C]
sub in trial 1 data to solve for k
1.5x10-3=k(0.100)2(0.200)
k=0.75
r=0.75[B]2[C]
PART FOUR: MAKING CONNECTIONS (4 marks)
1.
Using specific examples, explain how we use temperature, surface area, concentration and
catalysts in order to speed up the rate of chemical reactions to our advantage. (4 marks)