What is the main characteristic of an exothermic chemical reaction?

In an exothermic chemical reaction, the main characteristic is that heat is released as the reaction proceeds. This occurs because the total energy of the products formed during the reaction is lower than the total energy of the reactants. The excess energy that does not remain in the products is released into the surroundings, often in the form of thermal energy, which is perceived as an increase in temperature in the vicinity of the reaction.

The release of heat is a fundamental property of exothermic reactions and can be observed in many everyday chemical processes, such as combustion, where burning fuels produces heat and light. This heat release is a critical factor in many natural and industrial processes, impacting everything from weather systems to energy generation.

The other answer choices do not accurately describe an exothermic reaction. While heat absorption is characteristic of endothermic reactions, and no heat change indicates an isothermal process (not typical of chemical reactions), the statement about only light being emitted does not encompass the heat aspect, which is essential for defining exothermicity.