Download Unit 12-Rates+EquilibriumWS

Chemistry I
Study Guideline – Unit 12
Reaction Rates and Equilibrium
____________________________________________________
By the end of this chapter, the skills you should be able to demonstrate
are:
1. Explain collision theory in terms of concentration, particle size and
catalysts.
2. Interpret energy diagram for activation energy and if a reaction is
endo or exothermic.
3. List and Explain the factors that influence reaction rates.
4. Interpret and express the meaning of the rate of a chemical reaction.
5. Describe and Determine reaction mechanisms for simple reactions.
6. Define chemical equilibrium in terms of reversible reactions.
7. Write the equilibrium constant for a reaction and Compute its value
from experimental data; Calculate concentrations of reactants or
products for a reaction.
8. Explain the concept of solubility product and solve problems using
the ion-product constant.
9. Explain Le Châtelier’s principle.
10. Apply Le Châtelier’s principle in predicting the direction of a
change in an equilibrium.
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
Chemistry: Reaction Rates and Equilibrium
Coronet: Film and video - 21 minutes
1. What does the reaction of iron and oxygen produce?
2. What affects the rate of reactions?
3. Where do reactions take place?
4. How does surface area affect reaction rate?
5. How does concentration affect reaction rate?
6. How does temperature affect reaction rate?
7. What does collision theory say about reaction rates?
8. How do catalysts speed up reactions?
9. Why can reactions be considered two-way processes?
10. What is it called when the forward and backwards reactions occur at the same rate?
11. How can equilibrium be upset?
12. What type of reaction is favored by the addition of heat?
13. How can you favor the exothermic reaction?
14. What is the Haber process used to make commercially?
15. Do catalysts change the equilibrium of a reaction?
page 2
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
TV: Ontario - Chemical Equilibrium
Six Ten minute segments
Please Answer the following question while you watch the video
1. Which way do energy and heat flow?
2. What is the second law of thermodynamics?
3.What is a steady-state?
4. What is the standoff between reactants and products called?
5. Is equilibrium is a reaction really a complete stop?
6. What is a dynamic equilibrium?
7. Upon what is the collision theory based?
8. What must two molecules have in order to react?
9. Does the shape of the distribution of kinetic energy really stay the same when you heat the sample?
10. Describe the chain mechanism?
11. What is Le Châtlier’s Principle?
12. Which side of the reaction is favored by adding heat?
13. In the reaction N2 + 3H2 --> 2NH3, if Volume and Temperature are maintained as constants, what will
happen to pressure? Why?
14. Which side of a reaction is favored by increasing pressure?
15. What is the general mathematical expression of the equilibrium constant?
16. What is the Haber process?
page 3
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
Potential Energy Diagrams
Answer the following questions based on this diagram
1. Which of the letters (a)-(f) in the diagram represents the potential
energy of the products?
1. _______
2. Which of the letters indicates the total potential energy of the activated complex?
2. _______
3. Which letter indicates the potential energy of the reactants?
3. _______
4. Which letter indicates the activation energy?
4. _______
5. Which letter indicates the heat of reaction?
5. _______
6. Is the reaction endothermic or exothermic?
6. _______
7. Which letter indicates the activation energy of the reverse reaction?
7. _______
8. Which letter indicates the heat of reaction of the reverse reaction?
8. _______
9. Is the reverse reaction endothermic or exothermic?
9. _______
10a. If a catalyst were added which lettered quantities, if any, would change
10a. _____
b. Would the activation energy increase, decrease or remain unchanged?
b. _____
c. Would the heat of reaction increase, decrease or remain unchanged?
c. _____
page 4
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
Reaction Rate
activated complex
catalyst
heterogeneous reaction
potential energy
activation energy
energy
homogeneous reaction
rate-determining step
angle
heat of reaction
kinetics
reaction mechanism
The branch of chemistry concerned with rates of chemical changes is called _______________. A
chemical change in which all of the reactants are in the same phase is called a(n) ____________
_________. One in which the reactants are in different phases is called a(n) ______________
__________. A substance that speeds up a chemical change without becoming permanently altered is
called a(n) _______________.
The series of steps by which reacting particles rearrange themselves to form products is called the
____________ _________. The slowest step in such a series is the ______–_____________ ________.
A short-lived, high-energy particle that is formed when reacting particles collide at the proper
____________ with the proper amount of ____________ is a(n) ______________ ___________. The
minimum amount of energy needed to form this particle is called the _____________ ___________.
Because this energy is stored in the particle, it is an example of ____________ _________. The products
and the reactants of any reaction have different amounts of this kind of stored energy. The difference
between these two amounts of energy is the ____________ ______ _____________.
Potential Energy Plots
The potential energy of substance involved in a reaction can be plotted versus the
progress of the reaction, as the process move from initial reactants, through activated
complex, to final products. On the grids below, plot energy diagrams and answer the
questions.
400
1. Potential energy of the reactants: 250 kJ
Potential energy of the activated complex: 350 kJ
300
Potential energy of the products: 300 kJ
Is the reaction endothermic or exothermic?
PE
(kJ)
200
How can you tell? What is the value of ΔH?
100
Reaction Progress
If a catalyst were added, what would happen to the diagram? What would happen to the energies of the
reactants, products and activated complex? What would happen to the rate of the reaction? Explain.
page 5
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
500
2. Potential energy of the reactants: 350 kJ
Activation Energy: 100 kJ
Potential energy of the products: 300 kJ
a. Is the reaction endothermic or exothermic?
How can you tell? What is the value of ΔH?
400
PE
(kJ) 300
200
100
b. What is the potential energy of the activated
complex? ________
Reaction Progress
c. If the concentration of the reactants were increased, what would happen to the diagram? What would
happen to the energies of the reactants, products and activated complex? What would happen to the rate?
Explain.
3. Potential energy of the reactants: 200 kJ
Potential energy of the activated complex: 400 kJ
ΔH = +150 kJ
a. Is the reaction endothermic or exothermic?
How can you tell?
400
300
PE
200
(kJ)
100
b. What is the potential energy of the
products? ________
Reaction Progress
c. If the temperature were increased, what would happen to the diagram? What would happen to the
energies of the reactants, products and activated complex? What would happen to the rate? Explain.
Potential energy of the activated complex _____
kJ
4. Potential energy of the reactants _____
Activation energy ________
Potential energy of the products ______
ΔH = ________
a. Is the reaction endothermic or exothermic?
How can you tell?
c. If an inhibitor were added, what would happen to the diagram? What would happen to the energies of
the reactants, products and activated complex? What would happen to the rate? Explain.
page 6
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
Factors Affecting Rate
The rates of chemical reactions depend upon a number of factors. These factors can be
controlled by scientists in order to proceed at a desired rate. For each of the following
factors, write the probable effect (increase, decrease, no effect) on rate and then explain the
effect on the basis of collision theory.
Factor
Effect of Rate
Explanation
Decreased Concentration
Increased Gas Pressure
Decreased Temperature
Decreased surface area
Addition of catalyst
Addition of inhibitor
The Concept of Equilibrium
MATCHING
_____ 1. the formation of products from reactants
a. reversible reaction
_____ 2. a chemical reaction in which the products can regenerate
the original reactants
_____ 3. the speed at which a reaction occurs
b. chemical equilibrium
_____ 4. the regeneration of reactants from products
d. reaction rate
_____ 5. the state in which the concentrations of the reactants and
products remains constant with time
e. forward reaction
c. reverse reaction
6. Explain how reaction rate and equilibrium are related.
7. In performing most calculations with chemical reactions, it is assumed that the reactants are entirely
consumed. Is this assumption always appropriate? Explain.
8. Can all reversible reaction be observed in the laboratory? Why or why not?
page 7
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
9. What factors control the rate of a reaction?
10. How is concentration of reactants related to the rate of a reaction?
11. You place nitrogen gas and hydrogen gas into a sealed evacuated chamber with no product. The
reaction is sparked and ammonia gas is produced. How do the reaction rates and concentrations
change as the reaction proceeds?
12. Why will any reversible chemical reaction reach equilibrium in a closed system?
13. Does a reaction stop once it has reached equilibrium? Explain.
Chemical Equilibrium Constant
MATCHING
_____ 1. equilibrium position
_____ 2. law of chemical equilibrium
_____ 3. homogeneous equilibria
_____ 4. heterogeneous equilibria
_____ 5. equilibrium constant
a. equilibrium condition for reactions in which the
reactants and the products are in the same state.
b. the ratio of the product concentration to the
reactant concentration at equilibrium
c. Depends on the initial concentration of the
substances in a reaction
d. states that every reaction proceeds to an
equilibrium state with a specific Keq.
e. equilibrium condition for a chemical reaction
involving substances in more than one state.
6. What is the equilibrium expression for the synthesis of hydrogen iodide from its elements?
2
Answer: H2(g) + I2(g) <----> 2HI(g) >>> keq = [HI] /[H2][I2]
7. What is the equilibrium expression for the decomposition of solid ammonium chloride into ammonia
gas and hydrochloric acid gas?
Answer: NH4Cl(s) <----> NH3(g) + HCl(g) >>> keq = [NH3][HCl]
only gases and aqueous solutions are used in the equilibrium expression.
8. What is the equilibrium expression for the reaction of solid As4O6 with solid carbon to produce As4
gas and carbon monoxide gas?
9. What is the equilibrium expression for the reaction of solid tin(IV) oxide with carbon monoxide gas to
produce solid tin and carbon dioxide gas?
page 8
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
10. What is the equilibrium expression for the decomposition of solid calcium carbonate to produce solid
calcium oxide and carbon dioxide gas?
11. For the reaction where COCl2 gas decomposes to carbon monoxide gas and chlorine gas when
measured at equilibrium the following concentrations were found: each of the products = 0.150 M;
reactant = 1.10 x 10
–3
M. What is the Keq for this reaction?
12. For the reaction where methane gas reacts with liquid water to yield carbon monoxide gas and
hydrogen gas when measured at equilibrium the following concentrations were found: methane =
0.150 M; carbon monoxide = 0.259 M; hydrogen = 0.513 M. What is the Keq for this reaction?
13. For the reaction where carbon monoxide gas yields solid carbon and carbon dioxide gas, keq = 7.7 x
–15
10
. At a particular time, the following concentrations were measured: carbon monoxide = 0.034
–17
M; carbon dioxide = 3.6 x 10
M. Determine if this reaction is at equilibrium. If not determine in
which direction the reaction will proceed.
14. For the reaction where dinitrogen tetroxide gas yields nitrogen dioxide gas, keq = 0.2. At a particular
time, the following concentrations were measured: dinitrogen tetroxide = 2.0 M; nitrogen dioxide =
0.2 M. Determine if this reaction is at equilibrium. If not determine in which direction the reaction
will proceed.
15. For the reaction where iodine monochloride gas decomposes into iodine solid and chlorine gas, keq =
0.11. At a particular time, the following concentrations were measured: iodine chloride = 2.5 M;
chlorine = 1.2 M. Determine if this reaction is at equilibrium. If not determine in which direction the
reaction will proceed.
Match each statement with the appropriate letter. Each letter can be used once, more than
once or not at all
_____ 16. The equilibrium concentrations of products is much greater
than that of reactants
_____ 17. The equilibrium concentrations of products is much less
than that of reactants
_____ 18. The equilibrium concentrations of both products and
reactant is about the same.
page 9
a. Keq is much greater than 1
b. Keq is about equal to 1
c. Keq is much less than 1
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
17. What effect does changing the initial concentration of substances have on the equilibrium constant?
18. What is meant when scientists say “Equilibrium position lies to the left”?
19. Why are solids and pure liquids left out of the equilibrium expression?
20. The decomposition of phosphorus pentachloride into phosphorus trichloride and chlorine gas is a
reversible reaction that reaches a state of equilibrium. One mole of phosphorus pentachloride is is
placed in a sealed one liter container and heated to 250°C. The concentrations of the reactant and
products are measured in ten minute intervals. Plot the data from the following table on the graph
below:
Concentrations (mole per liter)
Time (seconds)
PCl5
1.00
0.90
0.85
0.82
0.80
0.80
0.80
0
10
20
30
40
50
60
PCl3
0.00
0.10
0.15
0.18
0.20
0.20
0.20
Cl2
0.00
0.10
0.15
0.18
0.20
0.20
0.20
0.9
0.7
Concentration
(mol/L)
0.5
0.3
0.1
0
10
20
30
40
Time (seconds)
a. How long did it take for the reaction to reach equilibrium?
50
60
b. What is the equilibrium concentration of each reaction component?
c. Does it make sense that the equilibrium concentration of each of the products is the same? Why?
page 10
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
Applying Le Châtelier’s Principle
The synthesis of hydrogen iodide gas from its elements is a reversible exothermic chemical reaction.
In the laboratory the hydrogen and iodine gases are sealed in the reaction flask. The gases then react
to become hydrogen iodide gas until equilibrium is established. The concentrations of the reactants
and the products are plotted in the graph that follows. Assume equilibrium is reached at point Te.
The following changes are introduced at time tf. Determine which situation best describes how the
graph would be changed to the right of tf.
A. Concentration of iodine gas is increased:
I. The hydrogen iodide curve rises, the iodine curve drops and the hydrogen curve remains the
same.
II. The hydrogen iodide curve drops, the iodine curve rises and the hydrogen curve drops.
III. The hydrogen iodide curve rises, the iodine curve rises and the hydrogen curve drops.
B. Temperature of the system is increased:
I. The curves for all three components rise.
II. The iodine and the hydrogen curves rise, the hydrogen iodide curve drops.
III. The iodine and the hydrogen curves drop, the hydrogen iodide curve rises.
C. Pressure of the system is increased:
I. The curves for all three components rise.
II. The iodine and the hydrogen curves drop, the hydrogen iodide curve rises.
III. All curves remain the same.
D. If a catalyst is present at the initial introduction of reactants, how would the graph differ?
page 11
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
Le Châtelier’s Principle
Match the change to the equilibrium system below with the appropriate letter. Each letter
can be used once, more than once or not at all
Sulfur Dioxide gas plus oxygen gas yields sulfur trioxide gas plus heat
_____ 1. Oxygen gas is added to the reaction
a. The reaction shifts to the right
_____ 2. Sulfur trioxide is removed from the system
b. The reaction shifts to the left
_____ 3. Sulfur trioxide is added to the system
c. There is no change in the equilibrium
position
_____ 4. The pressure is increased
If the statement is true write “true”. If it is false change the underlined word(s) to make
the statement true.
ammonium chloride solid plus heat decomposes into ammonia gas and hydrochloric acid gas
___________ 5. The above reaction is endothermic.
___________ 6. The production of ammonia from ammonium chloride will increase at higher
temperature.
___________ 7. In the above reaction system, the value of Keq decreases as the temperature increases.
___________ 8. For the above system at equilibrium, an increase in pressure on the system causes a
decrease in the number of moles of gaseous ammonia.
For each of the following systems at equilibrium, predict the effects of the given change on
the concentration of the specific substances. If the concentration increases draw an up
arrow. If it decrease draw a down arrow and if remains the same draw a dash.
When heated ammonia gas decomposes into nitrogen gas and hydrogen gas
1. Change: increase in nitrogen concentration. What is the effect on?
ammonia concentration _____
hydrogen concentration ________
2. Change: increase in temperature. What is the effect on?
Nitrogen concentration _____
ammonia concentration ________
3. Change: increase in the pressure. What is the effect on?
number of moles of nitrogen ______
number of moles of Ammonia ______
page 12
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
nitrogen monoxide gas decomposes into nitrogen gas and oxygen gas and heat
4. Change: decrease in oxygen concentration. What is the effect on?
Nitrogen concentration _____
nitrogen monoxide concentration ___
5. Change: decrease in temperature. What is the effect on?
oxygen concentration ______
nitrogen monoxide concentration ___
6. Change: increase in the pressure. What is the effect on?
number of moles of oxygen _______
number of moles of nitrogen monoxide _____
Arsenic, As4, is obtained from nature by first reacting its ore with oxygen (called roasting) to form solid
As4O6. (As4O6, a toxic compound fatal in doses of 0.1 g or more, is the “arsenic” made famous in
detective stories.) The As4O6 is then poisonous to the body when it is reduced by Carbon as follows:
As4O6 solid plus solid carbon produces As4 gas and carbon monoxide gas
7. Change: increase in carbon monoxide concentration. What is the effect on?
As4O6 concentration _______
As4 concentration __________________
8. Change: increase in As4O6 grams. What is the effect on?
carbon concentration ___________
As4 concentration __________________
9. Change: decrease in the pressure. What is the effect on?
number of moles of As4O6 ______
number of moles of carbon monoxide ___
10. State Le Châtelier’s principle
11. What factors alter the equilibrium position in chemical reactions?
12. If more reactant is added to an equilibrium system, what happens to Keq for the reaction?
13. How is changing the concentration of a reactant in a reaction related to a shift in equilibrium position?
14. For the reversible reaction: Nitrogen dioxide gas yields dinitrogen tetroxide gas, what will happen if
pressure is increased? Why?
page 13
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
15. How was La Châtelier’s principle used by Haber?
16. What is the effect of increasing temperature on the equilibrium constant of an exothermic reaction?
An endothermic reaction?
17. You are asked to produce hydrogen iodide from its elements. Write the equilibrium expression for
this reaction and explain the conditions you would use to maximize the amount of hydrogen iodide
produced.
The oxidation of ammonia is a reversible exothermic reaction with the
following word equation
ammonia gas plus oxygen gas yields nitrogen monoxide gas plus water vapor
Le Chatelier’s principle allows up to predict the changes that occur in an equilibrium reaction to
compensate for any stress that is placed upon the system. For each situation that is described if the
concentration increases draw an up arrow. If it decrease draw a down arrow and if remains the same draw
a dash.
Component
Stress
Equilibrium Concentrations
Ammonia
Ammonia
Oxygen
addition
▲
removal
▼
Oxygen
addition
▲
removal
▼
Nitrogen
monoxide
water vapor
Nitrogen
addition
▲
Monoxide
removal
▼
Water
addition
▲
Vapor
removal
▼
Increase in temperature
Decrease in temperature
Increase in pressure
Decrease in pressure
Addition of a catalyst
page 14
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
On the line at the left, indicate if the solubility of the solute increases, decrease, or remains
the same for each situation
___________ A. raising the temperature of a liquid solution, if the temperature remains constant when a
solid solute is mixed with the solvent.
___________ B. raising the temperature of a liquid solution, if the temperature rises when a solid solute
is mixed with the solvent.
___________ C. raising the temperature of a liquid solution, if the temperature drops when a solid solute
is mixed with the solvent.
Equilibrium - Review
A chemical change in which the reactants can be re-formed from the products is called a(n) _________
__________. When forward and backwards reactions occur at the same ________, a state of _______
____________ exists. A(n) _______ ________ is used in the equation to symbolize this state.
According to the law of chemical equilibrium, the __________ ___________, symbolized by ______,
is numerically equal to the fraction formed by the ___________ of the __________ over the _________
of the __________ raised to a power equal to the ___________ of each from the __________ _________.
When not at equilibrium, this calculation yields a value labeled as Q. If Q is greater than _____, the
reaction must proceed towards the __________ in order to reach equilibrium. If Q is less than _____, the
reaction must proceed towards the __________ in order to reach equilibrium.
When conditions such as temperature are changed, a chemical reaction is said to be placed under a(n)
_________. Under such changing conditions, equilibrium can undergo a(n) ________ in the direction
that tends to counteract the imposed changes. This generalization is known as __________ __________,
which has been applied to the manufacture of ammonia by a method called the _______ __________.
Equilibrium Crossword
ACROSS
1. State of matter
5. Basic unit of a crystal
6. Opposite of reverse
9. A reaction that proceeds more slowly than
another has a _____________ (2 words)
10. Point on a wave with zero amplitude
12. Moles per liter, for example
15. Symbol for selenium
17. Describes forward and reverse rates for a
system at equilibrium.
18. Element 8
19. Same as 13 down
22. Equilibrium is indicated by a double _____.
23. Substances with equal average molecular
kinetic energies have equal ___________.
26. Formula for silver iodide
29. Singular of 23 across
30. Charged particles
page 15
Unit 12-Rates+EquilibriumWS.doc
Dr. Corell - Chemistry I
DOWN
1. Symbol for Germanium
2. Symbol for element 13
3. A reaction with a low rate is said to be ____
4. Speed of a reaction
5. Symbol for calcium
7. To change chemically
8. Mass divided by volume
9. French chemist
11. Having a high value of 8 down
13. State in which forward and reverse reaction rates
are the same
1
2
14. Having to do with the smallest particles of an
element
16. Measure of randomness
17. Two words meaning same amounts
20. Not malleable
21. Measure of the amount of matter
24. Letters used to stand for “for example”
25. To give off light energy
27. Formula for potassium bromide
28. Formula for carbon monoxide
3
4
5
6
7
8
9
10
12
13
11
14
15
17
18
19
20
21
22
23
24
25
26
28
27
29
30
page 16
16