Endothermic process

An endothermic process absorbs heat from its surroundings, transferring thermal energy into the system. Its enthalpy change is positive when measured at constant pressure.

Enthalpy: A thermodynamic state function equal to a system’s internal energy plus pressure multiplied by volume. At constant pressure, an endothermic process has a positive enthalpy change.
Melting: The phase transition in which a solid becomes a liquid. A substance absorbs heat to overcome the attractions maintaining its solid structure.
Exothermic process: A process that transfers heat from a system to its surroundings. It reverses the direction of heat transfer that defines an endothermic process.
Instant cold pack: A portable cooling pack that becomes cold when separated chemicals are mixed and dissolve. Its endothermic dissolution removes heat from the pack and nearby skin.
Heat: Energy transferred between systems because of a temperature difference. Endothermic processes take in heat from their surroundings.
Vaporization: The phase transition in which a liquid becomes a gas. The liquid absorbs heat as particles separate into the gas phase.
Spontaneous process: A process that proceeds without continuous external intervention under specified conditions. Heat absorption alone does not determine whether a process occurs spontaneously.
Evaporative cooling: Cooling caused when higher-energy molecules escape from a liquid into a gas. Evaporation absorbs heat from the liquid and its surroundings.
First law of thermodynamics: The principle that energy is conserved, changing form or moving between systems but not being created or destroyed. Absorbed heat changes the system’s energy rather than creating energy.
Sublimation: The phase transition in which a solid changes directly into a gas. The solid takes in heat without passing through a liquid phase.

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CalcinationRelated: Many calcination reactions require continuous heat input to proceed.