Endothermic

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This article is about the physical effect. For self-maintained thermal homeostasis, see Warm-blooded.

In thermodynamics, the word endothermic describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning “inside” and the Greek suffix –thermic, meaning “to heat”.

The concept is frequently applied in physical sciences to e.g. chemical reactions, where chemical bond energy is converted to thermal energy (heat).

1 Overview
- 1.1 Endothermic processes
2 Implications for chemical reactions
3 Applications of endothermic processes
- 3.1 Endothermic materials in passive fire protection
4 See also
5 References
6 External links

[edit] Overview

Endothermic refers to a transformation in which a system receives heat from the surroundings:

Q > 0

When the transformation occurs at constant pressure:

∆H > 0

and constant volume:

∆U > 0

If the surroundings do not supply heat (e.g., when the system is adiabatic), an endothermic transformation leads to a drop in the temperature of the system.^[1]

[edit] Endothermic processes

Some examples of endothermic processes are

Cooking food
Melting of ice
Depressurising a pressure can

[edit] Implications for chemical reactions

Main article: endothermic reaction

Chemical endothermic reactions need heat to be performed. In a thermochemical reaction that is endothermic, the heat is placed on the reactants side (heat is necessary for and absorbed during the reaction).

[edit] Applications of endothermic processes

[edit] Endothermic materials in passive fire protection

Main article: Passive fire protection

Endothermic substances, both natural, e.g. gypsum, and synthetic, e.g. resin-based intumescents, are popular for use in heatshielding, ablation, materials in space physics, fireproofing, e.g. fire-resistive coatings for LPG vessels, and compartmentalisation of fire in buildings, which is the cornerstone of passive fire protection. Typically, the technological basis is the conversion of hydrates, or chemically bound water into vapour, or steam.

Typically, passive fire protection materials are required to keep the unexposed side of an assembly that is required to have a fire-resistance rating at or below 140°C for a defined duration. Since the water boiling point is 100°C, this is cool, compared against the benchmark of 140°C on average or 180°C for single hot spots. While the endothermic materials used in PFP still contain unspent hydrates, the unexposed side still maintains its rating.

Common endothermic building materials include concrete and gypsum wallboard. There are also various proprietary endothermic materials, which are typically organic, either water-based or inside an epoxy matrix for exterior use. Intumescents are typically endothermic to some degree.