Thermodynamic potential facts for kids

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In thermodynamics, thermodynamic potentials are parameters associated with a thermodynamic system and have the dimensions of energy. They are called "potentials" because in a sense, they describe the amount of potential energy in a thermodynamic system when it is subjected to certain constraints. The different potentials correspond to different constraints to which the system may be subjected. The four most common thermodynamic potentials are:

Name	Formula	Natural variables
Internal energy	$U\,$	$~~~~~S,V,\{N_i\}\,$
Helmholtz free energy	$A=U-TS\,$	$~~~~~T,V,\{N_i\}\,$
Enthalpy	$H=U+pV\,$	$~~~~~S,p,\{N_i\}\,$
Gibbs free energy	$G=U+pV-TS\,$	$~~~~~T,p,\{N_i\}\,$

where T = temperature, S = entropy, p = pressure, V = volume. The Helmholtz free energy is often denoted by the symbol F, but the use of A is preferred by IUPAC (See Alberty, 2001). $N_i$ is the number of particles of type i in the system. For the sake of completeness, the set of all $N_i$ are also included as natural variables, although they are sometimes ignored.

Thermodynamic potential facts for kids

See also