What conditions must be met in order for a reaction to be considered exothermic?

When the combined strength of the chemical bonds in the products is greater than the bonds in the reactants, a chemical reaction is said to be exothermic, releasing energy in the form of heat.

In an exothermic reaction, such as the burning of gasoline with oxygen to produce carbon dioxide and water (both of which have unusually strong bonds), the total energy of the electrons is lowered when a chemical reaction results in stronger chemical bonds in the products compared to reactants. Overall, energy must be conserved, so the excess energy of the products is typically released as heat. An example of this type of reaction is the N-N triple bond in nitrogen gas, which has a lower potential energy and kinetic energy than a weak chemical bond, such as the Br-Br single bond in bromine gas.

The opposite can occur under less common conditions: if the products' bonds are weaker than those of the reactants, the reaction is endothermic, which necessitates the removal of heat from the environment, resulting in lower product temperatures than reactant temperatures.

For a reaction to be considered exothermic, it must release energy in the form of heat to the surroundings. This typically occurs when the energy of the products is lower than the energy of the reactants.