IB Chemistry Equilibrium Review Questions from old IB exams
Equilibrium:
1. A chemical reaction has reached equilibrium when
a) the reverse reaction begins
b) the forward reaction stops
c) the concentrations of the reactants and products become equal
d) the rates of the forward and reverse reaction become equal
Answer: D
2. Double arrows pointing in opposite directions indicate that the reaction is
A) reversible
B) complete
C) static
D) balanced
Answer: A
3. When equilibrium has been reached in a chemical reaction,
a) all reaction stops
b) none of the reactants remain
c) the concentrations of the reactants and products are equal
d) the products react as quickly as they are formed.
Answer: D
4. Nitrogen, hydrogen and ammonia gases are placed in a container and allowed to reach
equilibrium. Which of the following statements about the equilibrium system is
correct?
a) The forward and the reverse reactions occur at the same rate.
b) The system contains equal amounts of reactants and products
c) Addition of a solid phase catalyst will increase the amount of ammonia
present.
d) All reactions have stopped.
Answer: A
5. Which one of the following would NOT affect the rate of a given chemical reaction?
a) The magnitude (size) of the equilibrium constant
b) The size of the solid reactant particles
c) The reaction temperature
d) The concentration of the reactants
Answer: A
Equilibrium Expression:
6. Which one of the following mass-action expressions is the correct statement of the
equilibrium law for the reaction: FeO(s) + CO(g)   Fe(s) + CO2(g)
a) K = [Fe][CO2]
[FeO][CO]
b) K = [Fe][CO]
[Fe][CO2]
c) K = [CO2]
[CO]
d) K = [CO]
[CO2]
Answer: D
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7. For the equilibrium system given: Cu2+(aq) + Zn(s) <= => Cu(s) + Zn2+(aq), the
correct for the equilibrium constant expression is:
a) Kc = [Cu][Zn2+]
[Cu2+][Zn]
b) Kc = [Cu2+][Zn]
[Cu][Zn2+]
c) Kc = [Cu2+]
[Zn2+]
d) Kc = [Zn2+]
[Cu2+]
Answer: D
Le Chatelier’s Principle:
8. In the equilibrium system, 2 SO2(g) + O2(g)   2 SO3(g) + heat, the
concentration of SO3(g) may be increased by:
A) increasing the pressure
B) decreasing the concentration of sulfur dioxide
C) increasing the temperature
D) decreasing the concentration of oxygen
Answer: A
9. When a catalyst is added to a system at equilibrium, there is a decrease in the
activation energy of
A) the forward reaction
B) the reverse reaction
C) both the forward and reverse reactions D) neither reaction
Answer: C
10. Which of the following reaction parameters would be affected by the addition of a
catalyst?
I.
Reaction rate
II.
Enthalpy of reaction
III.
Equilibrium position
a) I only
b) I and II only
c) II and III only
d) I, II and III only
Answer: A
11. Which one of the following will change the value of the equilibrium constant for the
reaction between hydrogen, H2(g), and iodine, I2(g)?
a) Increasing the pressure at a constant temperature
b) Increasing the concentration of the reactants
c) Increasing the concentration of the products
d) Increasing the temperature of the system.
Answer: D
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12. If the system shown is at equilibrium, which one of the following changes will
increase the equilibrium amount of H2(g) which follows the equation:
H2(g) + I2(g)   2 HI(g), H = -60 kJ
a) Increase in pressure at a constant temperature
b) Addition of a solid-phase catalyst
c) Addition of I2(g)
d) Increase in temperature
Answer: D
13. The system CO2(g) + H2(g)   H2O(g) + CO(g) is allowed to reach equilibrium.
The amount of carbon monoxide, CO, present in the equilibrium mixture can be
increased by
a) increasing the pressure on the mixture.
b) Removing some carbon dioxide
c) Adding a catalyst
d) Adding hydrogen
Answer: D
14. Which one of the following changes below will alter the value of the equilibrium
constant, K, for the following molecular equilibrium in a sealed container?
H2(g) + Br2(g)   2HBr(g)
H = -72.8 kJ
a) Adding more hydrogen to the container without changing its volume
b) Heating the system
c) Adding some neon to the container without changing its volume
d) Raising the pressure of the system by 10 %
Answer: B
15. All of the following equilibria would be affected by volume changes at constant
temperature EXCEPT:
a) N2O4(g)   2 NO2(g)
b) C(s) + H2O(g)   CO(g) + H2(g)
c) NO(g) + 1/2O2(g)   NO2(g)
d) CH4(g) + Cl2(g)   CH3Cl(g) + HCl(g)
Answer: D
16. The numerical value of the equilibrium constant for a chemical change may be altered
by changing the
a) pressure of the system
b) temperature of the system
c) concentration of the products in the system
d) concentration of the reactants in the system
Answer: B
17. Consider the equilibrium: 2 NO2(g)   2 NO(g) + O2(g) H = +113 kJ If the
temperature of the reaction system is increased, then
a) [NO] increases and [NO2] decreases.
b) [NO] decreases and [NO2] increases.
c) [NO], [O2] and [NO2] all increase.
d) [NO], [O2] and [NO2] all decrease.
Answer: A
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18. Heat is evolved when a certain solid is dissolved in water. How will an increase in
temperature affect the solubility of the solid? Why?
19. What is meant by ‘dynamic equilibrium”?
The Haber Process:
20. The production of ammonia is one of the world's most important chemical processes.
a) Write a balanced chemical equation, which represents this process.
b) The reactants are subjected to high heat and pressure. Explain why with is done.
c) State two major uses of ammonia.
d) State the catalyst used.
The Contact Process:
21. The contact process is used to make sulphuric acid. The process requires three
reactions.
a) Write the balanced chemical equations for the reactions, which are needed to
make sulphuric acid.
b) Describe the conditions necessary for the second step and use Le Chatelier’s
principle to explain why the conditions will maximize the production of sulfur
trioxide.
c) State the catalyst used in this reaction.
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