What does a negative enthalpy change indicate about a chemical reaction?

A negative enthalpy change indicates that a chemical reaction releases heat to the surroundings, which characterizes the reaction as exothermic. This means that during the reaction, the total energy of the products is less than that of the reactants, resulting in the release of energy in the form of heat. Such reactions typically cause an increase in the temperature of the surroundings.

In contrast, an endothermic reaction would have a positive enthalpy change, demonstrating that heat is absorbed from the surroundings. Additionally, if the reaction occurs at equilibrium, the enthalpy change would theoretically be zero, reflecting no net change in energy as reactants are converted into products and vice versa. Thus, the identification of a negative enthalpy change clearly signals an exothermic process where energy is expelled, explaining why this choice is correct.