MCQs on Le Chatelier Principle and its Application

When a reaction reaches equilibrium, the forward and reverse reactions take place at the same rate, and the equilibrium concentration of the reaction mixture does not change as long as we don’t do anything to the system. But what happens in opposite? In 1888, Henry Le Chatelier put forth the statement known as the Le Chatelier principle. If external stress is applied to a system in equilibrium, the system reacts in such a way as to partially relieve that stress. It is the principle stating that when a stress is applied to a system in chemical equilibrium, the position of the equilibrium shifts in the direction that will relieve the applied stress.

1. In what manner will increase of pressure affect the following equation

C(s) + H2O → CO(g) + H2(g)

  1. shift in the reverse direction
  2. shift in the forward direction
  3. increase in the yield of hydrogen
  4. no effect

Answer: (a)

2. The equilibrium between water and its vapour in an open vessel

  1. can be achieved
  2. depends upon pressure
  3. cannot be achieved
  4. depends upon temperature

Answer: (c)

3. When a catalyst is added to a reversible reaction in equilibrium state the value of the equilibrium constant

  1. increases
  2. decreases
  3. does not change
  4. becomes zero

Answer: (c)

4. A vessel at equilibrium contains SO3, SO2 and O2, now some helium gas is added so that total pressure increases while temperature and volume remain constant. According to Le Chatelier Principle the dissociation of SO32-

  1. decreases
  2. remain constant
  3. increases
  4. change unpredictably

Answer: (b)

5. The chemical equilibrium of a reversible reaction is not influenced by

  1. temperature
  2. pressure
  3. catalyst
  4. concentration

Answer: (c)

6. Le Chatelier Principle is applicable to

  1. heterogeneous reaction
  2. homogeneous reaction
  3. irreversible reaction
  4. system in equilibrium

Answer: (d)

7. The equilibrium constant of a reaction is 300. If the volume of reaction flask is tripled the equilibrium constant is

  1. 300
  2. 600
  3. 900
  4. 100

Answer: (a)

8. For a reversible reaction the concentration of the reactants are doubled, then the equilibrium constant

  1. becomes one-fourth
  2. is doubled
  3. is halved
  4. remains the same

Answer: (d)

9. The role of a catalyst in a reversible reaction is to

  1. alter the equilibrium constant of the reaction
  2. increase the rate of the forward reaction
  3. allow the equilibrium to be achieved quickly
  4. decrease the rate of backward reaction

Answer: (c)

10. In which of the following cases does the reaction go farthest to completion?

  1. K = 1
  2. K = 10
  3. K = 10-2
  4. K = 102

Answer: (d)



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