Exothermic process

In thermodynamics, an exothermic process (from Ancient Greek έξω (éxō) 'outward', and θερμικός (thermikós) 'thermal')^[1] is a thermodynamic process or reaction that releases energy from the system to its surroundings,^[2] usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e.g. a battery), or sound (e.g. explosion heard when burning hydrogen). The term exothermic was first coined by 19th-century French chemist Marcellin Berthelot.^[3]

The opposite of an exothermic process is an endothermic process, one that absorbs energy, usually in the form of heat.^[2] The concept is frequently applied in the physical sciences to chemical reactions where chemical bond energy is converted to thermal energy (heat).