The Response of Equilibria to the Conditions

According to Le Chatelier's principle, when a system at equilibrium is subjected to a change, the composition of the system adjusts to counteract the effect of that change.

In an exothermic reaction, when the system's temperature increases, the equilibrium composition shifts toward the reactants, while in an endothermic reaction, it shifts toward the products.

The van’t Hoff equation shows how temperature changes affect the equilibrium constant.

For an endothermic reaction, the standard reaction enthalpy, Δ_rH°, is positive. Increasing the temperature shifts the equilibrium toward the products, raising the equilibrium constant.

For an exothermic reaction, Δ_rH° is negative; increasing the temperature decreases the equilibrium constant, producing fewer products.

In gas-phase equilibria, increasing pressure favors the side with fewer gas molecules, while decreasing pressure favors the side with more gas molecules.

If both sides have an equal number of gas molecules, pressure has no effect on the equilibrium.

A catalyst increases the rates of both forward and reverse reactions equally, so it does not alter the equilibrium position or the equilibrium constant.