1.	Which statement about chemical equilibria implies they are dynamic?
A.	The position of equilibrium constantly changes.
B.	The rates of forward and backward reactions change.
C.	The reactants and products continue to react.
D.	The concentrations of the reactants and products continue to change.
(Total 1 mark)

2.	An example of a homogeneous reversible reaction is the reaction between hydrogen and iodine.
		H_2(g) + I_2(g)  2HI(g)
(i)	Outline the characteristics of a homogeneous chemical system that is in a state of equilibrium.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)
 
(ii)	Deduce the expression for the equilibrium constant, K_c.
......................................................................................................................................
......................................................................................................................................
(1)
 
(iii)	Predict what would happen to the position of equilibrium and the value of K_c if the pressure is increased from 1 atm to 2 atm.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)

(iv)	The value of K_c at 500 K is 160 and the value of K_c at 700 K is 54. Deduce what this information tells us about the enthalpy change of the forward reaction.
......................................................................................................................................
......................................................................................................................................
(1)
 
(v)	The reaction can be catalysed by adding platinum metal. State and explain what effect the addition of platinum would have on the value of the equilibrium constant.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)
(Total 8 marks)

3.	The sequence of diagrams represents the system as time passes for a gas phase reaction in which reactant X is converted to product Y.

	Which statement is correct?
A.	At t = 5 days the rate of the forward reaction is greater than the rate of the backward reaction.
B.	At t = 7 seconds the reaction has reached completion.
C.	At t = 10 minutes the system has reached a state of equilibrium.
D.	At t = 5 days the rate of the forward reaction is less than the rate of the backward reaction.
(Total 1 mark)

4.	Methanol may be produced by the exothermic reaction of carbon monoxide gas and hydrogen gas.
		CO(g) + 2H_2(g)  CH_3OH(g)	∆H~~^O~~ = –103 kJ

(a)	State the equilibrium constant expression, K_c, for the production of methanol.
......................................................................................................................................
......................................................................................................................................
(1)
 
(b)	State and explain the effect of changing the following conditions on the amount of methanol present at equilibrium:
(i)	increasing the temperature of the reaction at constant pressure.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
 
(ii)	increasing the pressure of the reaction at constant temperature.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
 
(c)	The conditions used in industry during the production of methanol are a temperature of 450 °C and pressure of up to 220 atm. Explain why these conditions are used rather than those that could give an even greater amount of methanol.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)

(d)	A catalyst of copper mixed with zinc oxide and alumina is used in industry for this production of methanol. Explain the function of the catalyst.
......................................................................................................................................
......................................................................................................................................
(1)
(Total 8 marks)

5.	(i)	A state of equilibrium can exist when a piece of copper metal is placed in a solution of copper(II) sulfate. Outline the characteristics of a chemical system in dynamic equilibrium.
(2)
 
(ii)	For an exothermic reaction state how an increase in temperature would affect both K_c and the position of equilibrium.
(2)
(Total 4 marks)

6.	Consider the endothermic reaction below.
		5CO(g) + I_2O_5(g)  5CO_2(g) + I_2(g)
	According to Le Chatelier’s principle, which change would result in an increase in the amount of CO_2?
A.	Increasing the temperature
B.	Decreasing the temperature
C.	Increasing the pressure
D.	Decreasing the pressure
(Total 1 mark)

7.	What effect will an increase in temperature have on the K_c value and the position of equilibrium in the following reaction?
		N_2(g) + 3H_2(g)  2NH_3(g)	ΔH = –92 kJ

| K_c | Equilibrium position
A. | increases | shifts to the right
B. | decreases | shifts to the left
C. | increases | shifts to the left
D. | decreases | shifts to the right
(Total 1 mark)

8.	The equation for the main reaction in the Haber process is:
	N_2(g) + 3H_2(g)  2NH_3(g)	∆H is negative
 
(i)	Determine the equilibrium constant expression for this reaction.
(1)
 
(ii)	State and explain the effect on the equilibrium yield of ammonia with increasing the pressure and the temperature.
(4)
 
(iii)	In practice, typical conditions used in the Haber process involve a temperature of 500 °C and a pressure of 200 atm. Explain why these conditions are used rather than those that give the highest yield.
(2)
 
(iv)	At a certain temperature and pressure, 1.1 dm^3 of N_2(g) reacts with 3.3 dm^3 of H_2(g). Calculate the volume of NH_3(g), that will be produced.
(1)
 
(v)	Suggest why this reaction is important for humanity.
(1)

(vi)	A chemist claims to have developed a new catalyst for the Haber process, which increases the yield of ammonia. State the catalyst normally used for the Haber process, and comment on the claim made by this chemist.
(2)
(Total 11 marks)

9.	What is the effect of an increase of temperature on the yield and the equilibrium constant for the following reaction?
		2H_2(g) + CO(g)  CH_3OH(l)	∆H~~^O~~ = –128 kJ

| Yield | Equilibrium constant
A. | Increases | Increases
B. | Increases | Decreases
C. | Decreases | Increases
D. | Decreases | Decreases
(Total 1 mark)

10.	What changes occur when the temperature is increased in the following reaction at equilibrium?
	Br_2(g) + Cl_2(g)  2BrCl(g)	∆H~~^ο~~ = +14 kJ mol^–1
| Position of equilibrium | Value of equilibrium constant
A. | Shifts towards the reactants | Decreases
B. | Shifts towards the reactants | Increases
C. | Shifts towards the products | Decreases
D. | Shifts towards the products | Increases
(Total 1 mark)

IB Questionbank Chemistry