Which process releases energy as heat to the surroundings?

The process that releases energy as heat to the surroundings is an exothermic process. In thermochemistry, exothermic reactions are characterized by the release of heat, resulting in a decrease in the internal energy of the system. This energy transfer occurs because the products of the reaction have lower energy compared to the reactants; as a result, the excess energy is emitted, often in the form of heat.

For example, when a chemical reaction occurs that is exothermic, it often results in an increase in the temperature of the surroundings. Common examples of exothermic processes include combustion reactions, such as burning wood or gasoline, where heat is released into the environment.

In contrast, endothermic processes absorb heat from their surroundings, leading to a cooling effect. Isothermal processes occur at a constant temperature, which does not directly indicate whether heat is released or absorbed. Reversible processes refer to the ability to return to the original state without net change, and they can be either endothermic or exothermic depending on the specific reaction. Thus, the defining characteristic of an exothermic process is its capacity to release heat, which is why it is the correct answer.