What happens to the molecules in an exothermic reaction?

In an exothermic reaction, the key characteristic is that the molecules release energy, typically in the form of heat. This means that during the reaction, the chemical bonds in the reactants are broken and new bonds in the products are formed, and the energy associated with the initial bonds is greater than that of the final products. The excess energy is released into the surroundings, making the environment warmer.

This energy release can be observed in various reactions, such as combustion, where a substance like fuel combines with oxygen and releases energy as heat and light. The release of energy is a defining feature of exothermic reactions, distinguishing them from endothermic reactions, in which energy is absorbed from the surroundings.