How does increasing pressure affect equilibrium?

Increasing pressure in a chemical equilibrium system generally favors the side of the reaction that has fewer moles of gas. This occurs because according to Le Chatelier's Principle, a system at equilibrium will respond to any change in conditions by favoring the direction that counteracts that change in order to establish a new equilibrium.

When pressure is increased, the system aims to reduce it by shifting the equilibrium position towards the side with fewer gas molecules. This results in a decrease in the total volume occupied by the gas, thereby alleviating the increase in pressure. In reactions where the number of gas molecules differs between reactants and products, this effect becomes particularly significant.

For example, in a reaction where two moles of gas react to form one mole of gas, increasing the pressure would shift the equilibrium towards the production of the product, which is the side with fewer moles of gas. Thus, the response to an increase in pressure is characterized by the system's tendency to minimize the disturbance caused by that increase, confirming why a shift to the side of fewer moles of gas is the correct response.