American Chemical Society (ACS) Chemistry Test 2025 – 400 Free Practice Questions to Pass the Exam

In an exothermic reaction, heat can be considered a product of the reaction. According to Le Chatelier's principle, if the temperature of a system at equilibrium is lowered, the equilibrium will shift in the direction that produces heat to counteract the temperature change. This means that the system will favor the forward reaction, which releases heat, thereby increasing the concentration of the products relative to the reactants.

When the concentration of the products increases, the equilibrium constant (K), which is defined as the ratio of the concentrations of the products to the concentrations of the reactants at equilibrium, will also increase. Thus, lowering the temperature in an exothermic reaction results in an increase in the equilibrium constant.

It's important to understand that this relationship is specific to exothermic reactions. In contrast, for endothermic reactions, lowering the temperature would decrease the equilibrium constant, as the system would favor the reverse reaction to absorb heat.