How does an increase in pressure affect a gas reaction at equilibrium?

An increase in pressure affects a gas reaction at equilibrium according to Le Chatelier's principle, which states that if a system at equilibrium experiences a change in conditions (such as pressure, temperature, or concentration), the system will adjust to counteract that change.

In the case of an increase in pressure, the equilibrium will shift in the direction that produces fewer moles of gas. This means that if the reaction involves gases on both sides, the side with the fewer total moles of gas will be favored. The reasoning behind this is that a decrease in the total number of moles of gas will lead to a decrease in volume, which counteracts the increase in pressure.

Therefore, in situations where the balanced chemical equation shows a difference in the number of moles of gas between reactants and products, the shift towards fewer moles upon increasing pressure results in an alteration in the concentration of reactants and products until a new equilibrium is established. This principle effectively illustrates the dynamic nature of chemical equilibria and how they respond to various changes in external conditions.