Question

For the reaction,
$2S{{O}_{2}}(g)+{{O}_{2}}(g)\rightleftharpoons 2S{{O}_{3}}(g)$ , $\Delta H$ = -57.2 kJ/mol and ${{K}_{c}}=1.7\times {{10}^{16}}$ .
Which of the following statements is INCORRECT?
A. The equilibrium constant is large suggestive of reaction going to completion and so no catalyst is required.
B. The equilibrium will shift in forward direction as the pressure increases
C. The equilibrium constant decreases as the temperature increases
D. The addition of inert gas at constant volume will not affect the equilibrium constant

Answer 1

. Le chatelier’s principle explains a concept that a change in concentration of the reactants or products or a change in pressure or a change in temperature of a chemical reaction shifts the equilibrium of the reaction towards reactant side or product side to nullify the changes.

Complete step by step answer:
- In the question it is given that 2 moles of the sulphur dioxide reacts with one moles of oxygen and forms 2 moles of the sulphur trioxide as the product.
- The given chemical reaction is
$2S{{O}_{2}}(g)+{{O}_{2}}(g)\rightleftharpoons 2S{{O}_{3}}(g)$

- We have to find the incorrect statement among the given options.
- Coming to given options, Option B, The equilibrium will shift in forward direction as the pressure increases. It is correct because if we increase the pressure then the volume decreases and the equilibrium shifts towards the side where less number of moles are present.
- In the given chemical reaction less number of moles (2 moles) are present in the product side. So, the equilibrium shifts towards the product side then option B is correct.

- Coming to option C, The equilibrium constant decreases as the temperature increases. From the question we can say that the given reaction is exothermic means energy is going to release.
- For exothermic reactions the equilibrium constant decreases while temperature increases. So, option C is also correct.

- Coming to option D, The addition of inert gas at constant volume will not affect the equilibrium constant. It is also correct because by introducing the inert gas in the given chemical reaction there is no change in the equilibrium constant because inert gas won’t react with any chemical which is present in the given reaction.
- So, option D is also correct.

- Coming to option A, The equilibrium constant is large suggestive of reaction going to completion and so no catalyst is required. It is wrong because there is a need for a catalyst to complete the reaction.
- For example vanadium pentoxide is used as a catalyst in the preparation of sulphur trioxide.
So, the correct answer is “Option A”.

Note: Generally catalysts have no effect on the equilibrium constant of the reaction. Because catalyst makes the forward and backward reaction to the same extent. Adding a catalyst does not change the rates of the two reactions so it cannot affect the equilibrium constant.