Exothermic process

An exothermic process releases heat from a system to its surroundings. At constant pressure, the system’s enthalpy change is negative.

Enthalpy: A thermodynamic state function whose change at constant pressure equals heat transferred to or from a system. Its change is negative for an exothermic process at constant pressure.
Heat: Energy transferred between bodies or systems because of a temperature difference. Exothermicity specifically describes heat crossing from the system to its surroundings.
Combustion: A rapid chemical reaction with an oxidant that releases energy, commonly as heat and light. Fuel combustion is a familiar chemical example of heat released to surroundings.
Endothermic process: A process that absorbs heat from its surroundings; at constant pressure, its enthalpy change is positive. It reverses the direction of heat transfer that defines exothermicity.
First law of thermodynamics: The principle that energy is conserved, changing form or moving between a system and its surroundings. It explains how released heat fits into the system’s overall energy balance.
Temperature: A physical quantity that characterizes thermal state and determines the direction of spontaneous heat transfer. Surroundings often warm during heat release, though temperature change is not the definition.
Neutralization: A reaction between an acid and a base that produces a salt and, often, water. Many aqueous acid–base neutralizations release heat.
Adiabatic process: A thermodynamic process in which no heat crosses the system boundary. An adiabatic process is neither exothermic nor endothermic by heat transfer.
Calorimetry: The measurement of heat transferred during physical, chemical, or biological processes. Calorimetry detects heat released by an exothermic process.
Thermodynamic process: A change that takes a thermodynamic system between states or through a sequence of states. Exothermicity classifies a process by the direction of its heat transfer.

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