Exothermic Reaction
A reaction that releases energy to the surroundings, giving a negative enthalpy change.
Formula / equation
ΔH < 0
Unit
kJ/mol
In depth
Energy is released because the bonds formed in the products are stronger overall than those broken in the reactants. The surroundings warm up, and the products lie lower on an energy profile than the reactants. Most spontaneous reactions at ordinary temperatures are exothermic.
Examples in the real world
Combustion, neutralisation, respiration, and the setting of concrete; a hand warmer crystallising sodium acetate.