Chemistry 40S
Revenge of Le Chatelier
1. 3 H2(g) + N2(g) ⇄ 2 NH3(g)
Given that this reaction is exothermic, what direction will the
equilibrium shift when the temperature of the reaction is decreased?
2. For the reaction:
CH4(g) + H2O(g) + 49.3 kJ ⇄ CO(g) + 3 H2(g)
predict the effect on the position of the equilibrium that results from:
a) increasing temperature.
b) decreasing temperature.
3. For the reaction
9.4 kJ + 2 HI(g) ⇄ H2(g) + I2(g)
a) What is the effect on [HI] if the temperature is increased?
b) What is the effect on [HI] if a catalyst is added?
4. For the reaction:
CO(g) + 2 H2(g) ⇄ CH3OH(g) + energy
predict the effect of decreasing the temperature of the system.
5. In the equilibrium reaction
2 NO(g) + O2(g)
2 NO2(g) + 114.6 kJ
What will be the change in the equilibrium [NO2] under each of the
following conditions?
a) O2 is added.
b) NO is removed.
c) energy is added.
Chemistry 40S
6. For the reaction
PCl3(g) + Cl2(g) ⇄ PCl5(g) ΔH = –92.5 kJ
predict the effect on the position of the equilibrium that results from
a) increasing the total pressure by decreasing volume.
b) injecting more Cl2 gas without changing the volume.
c) increasing the temperature.
d) increasing the volume of the container.
e) adding a catalyst.
7. For the following reaction, ΔH = +58.9 kJ:
N2O4(g) ⇄ 2 NO2(g)
How will the equilibrium [NO2] be affected by the following?
a) an increase in pressure.
b) an increase in temperature.
c) the addition of a catalyst.
8. The following system reaches equilibrium at 175 oC:
N2(g) + 3H2(g) ⇄ 2NH3(g) + heat
Once it reaches equilibrium, the following values are found for the
concentrations:
[N2] = 0.75 M
[H2] = 0.45 M
[NH3] = 1.5 M
a) What is KC at this temperature?
b) The temperature of the system is lowered to 150 oC. After the
system reaches its new equilibrium point, [NH3] is found to have
changed by 0.12 M. Will it have increased or decreased by this
amount?
c) Calculate the new KC for this temperature.
Chemistry 40S
Answers
1. Reaction will shift to the right to produce more heat.
2. a) Equilibrium will shift to the right to use up the extra heat.
b) Equilibrium will shift to the left to produce more heat.
3. a) [HI] will decrease, since the reaction shifts to the right.
b) There is no effect, since catalysts affect the forward and reverse
reactions equally.
4. Decreasing the temperature makes the system shift to the right.
5. a) [NO2] will increase, since the reaction shifts to the right.
b) [NO2] will decrease, since the reaction shifts to the left.
c) [NO2] will decrease, since the reaction shifts to the left.
6. a) Equilibrium will shift because the right side of the equation has
fewer particles.
b) The system will use up the added reactant by shifting towards the
products (right).
c) This system will respond by shifting the equilibrium to the left
(reactants) in order to use the added heat.
d) The system will shift to the left (reactants), since the reactants
have more particles.
e) Adding a catalyst does not affect the equilibrium position, just the
speed with which equilibrium is reached.
7. a) An increase in pressure will decrease the [NO2].
b) An increase in temperature will increase the [NO2].
c) The addition of a catalyst will not affect the equilibrium [NO2].
8. a) KC = 32.9
b) [NH3] will increase, since the system will try to produce more heat
by shifting right.
c) KC = 193