When ΔH is negative, a reaction is said to be

In chemistry, the term "ΔH" refers to the change in enthalpy of a chemical reaction. Enthalpy is a measure of the heat energy of a system. When ΔH is negative, it means that the reaction is releasing heat into the surrounding environment, and the reaction is said to be exothermic. In other words, the products of the reaction have less heat energy than the reactants, and the difference in heat energy is released as heat. On the other hand, when ΔH is positive, it means that the reaction is absorbing heat from the surrounding environment, and the reaction is said to be endothermic. In this case, the products of the reaction have more heat energy than the reactants, and the difference in heat energy is absorbed as heat. Therefore, the answer is - exothermic.