Effect of Dilution or Volume Change

Suppose we increase the volume of the above gas-phase equilibrium. The total pressure will decrease, and, according to Le Chatelier's principle, the system will respond to increase the total pressure. Since 3 mol of reactants is converted to 1 mol of products, a forward reaction decreases the total pressure, a reverse reaction increases the total pressure. Thus the equilibrium will shift to the left. Similarly a decrease in volume would lead to a shift to the right, forming more CH₃OH. A similar argument applies to the dilution of a solution phase equilibrium.