Latent heat

Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. An example is latent heat of fusion for a phase change, melting, at a specified temperature and pressure. The term was introduced around 1762 by Scottish chemist Joseph Black. It is derived from the Latin latere (to lie hidden). Black used the term in the context of calorimetry where a heat transfer caused a volume change while the thermodynamic system's temperature was constant.

In contrast to latent heat, sensible heat involves an energy transfer that results in a temperature change of the system.

The terms ″sensible heat″ and ″latent heat″ are specific forms of energy; they are two properties of a material or in a thermodynamic system. ″Sensible heat″ is a body's internal energy that may be ″sensed″ or felt. ″Latent heat″ is internal energy concerning the phase ( solid / liquid / gas ) of a material and does not affect the temperature.

Both sensible and latent heats are observed in many processes of transport of energy in nature. Changes of Latent heat is associated with the change of phase of atmospheric water, vaporization and condensation, whereas sensible heat is energy that reflects the temperature of the atmosphere or ocean, or ice.

The original usage of the term, as introduced by Black, was applied to systems that were intentionally held at constant temperature. Such usage referred to latent heat of expansion and several other related latent heats. These latent heats are defined independently of the conceptual framework of thermodynamics.

When a body is heated at constant temperature by thermal radiation in a microwave field for example, it may expand by an amount described by its latent heat with respect to volume or latent heat of expansion, or increase its pressure by an amount described by its latent heat with respect to pressure.

Two common forms of latent heat are latent heat of fusion (melting) and latent heat of vaporization (boiling). These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas.

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