Q. Show the Effect of pressure on chemical equilibrium?

Ans.

In gases, the pressure is proportional to the number of moles of molecules. Reactions accompanied by a change in the number of moles of gases are also affected by pressure changes. Reactions that are not accompanied by a change in the number of moles of gases are not affected by pressure changes. For example consider the following reaction:

2CO + O₂ -> 2CO₂

Note that in this reaction, the number of moles changes as there is a total of 3 moles of reactants on the left and 2 moles of product on the right. Therefore, a change in pressure will affect the equilibrium.

Here, an increase in pressure will shift the reaction to the right as predicted by Le Chtelier's principle. The right is the side with the fewer moles. Therefore, the increase in pressure will be minimized as the side with the fewer moles is favored.

Note: Reactions involving solids and liquids are usually not accompanied by large changes in volume. Hence, the effect of pressure change on reactions of solids and liquids is slight.