In thermodynamics, the Helmholtz free energy (or Helmholtz energy) is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature (isothermal). The change in the Helmholtz energy during a process is equal to the maximum amount of work that the system can perform in a thermodynamic process in which temperature is held constant. At constant temperature, the Helmholtz free energy is minimized at equilibrium.
In contrast, the Gibbs free energy or free enthalpy is most commonly used as a measure of thermodynamic potential (especially in chemistry) when it is convenient for applications that occur at constant pressure. For example, in explosives research Helmholtz free energy is often used, since explosive reactions by their nature induce pressure changes. It is also frequently used to define fundamental equations of state of pure substances.
The concept of free energy was developed by Hermann von Helmholtz, a German physicist, and first presented in 1882 in a lecture called "On the thermodynamics of chemical processes".[1] From the German word Arbeit (work), the International Union of Pure and Applied Chemistry (IUPAC) recommends the symbol A and the name Helmholtz energy.[2] In physics, the symbol F is also used in reference to free energy or Helmholtz function.
^von Helmholtz, H. (1882). Physical memoirs, selected and translated from foreign sources. Taylor & Francis.
Historically, the term 'freeenergy' has been used for either quantity. In physics, freeenergy most often refers to the Helmholtzfreeenergy, denoted by A (or...
variational freeenergy is based upon Helmholtz’s work on unconscious inference and subsequent treatments in psychology and machine learning. Variational free energy...
the energy available for non-pressure-volume work. (An analogous, but slightly different, meaning of "free" applies in conjunction with the Helmholtz free...
Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in...
}}(A_{0}(T_{0},x))} showing that the Helmholtzfreeenergy is minimized at equilibrium. The Enthalpy and Gibbs freeenergy, are similarly derived. Callen,...
potential) Helmholtzfreeenergy Variational freeenergy, a construct from information theory that is used in variational Bayesian methods Freeenergy device...
the total energy of the microstate, and k is the Boltzmann constant. The number F is the freeenergy (specifically, the Helmholtzfreeenergy) and is assumed...
occurring which cause them to change. The Helmholtzfreeenergy is in ISO/IEC standard called Helmholtzenergy or Helmholtz function. It is often denoted by the...
internal energy, specific enthalpy, specific Gibbs freeenergy, and specific Helmholtzfreeenergy. It may also be used for the kinetic energy or potential...
Gibbs freeenergy change is used when considering processes that occur under constant pressure and temperature conditions, whereas the Helmholtzfree energy...
The Helmholtz machine (named after Hermann von Helmholtz and his concept of Helmholtzfreeenergy) is a type of artificial neural network that can account...
isothermal elastic processes, the strain energy density function relates to the specific Helmholtzfreeenergy function ψ {\displaystyle \psi } , W = ρ...
flocculation of the colloids. The positive change in entropy lowers the Helmholtzfreeenergy and causes colloidal flocculation to happen spontaneously. The system...
variables are the internal energy U ( S , V ) {\displaystyle U(S,V)} , enthalpy H ( S , P ) {\displaystyle H(S,P)} , Helmholtzfreeenergy F ( T , V ) {\displaystyle...
internal energy and the Helmholtzfreeenergy.[citation needed] Geothermal energy Geothermal heating Geothermal power Heat transfer Ocean thermal energy conversion...
uniaxial tension P, then at equilibrium, the variation of the total Helmholtzfreeenergy vanishes and we have δ F = − P δ l + γ δ A = 0 ⟹ γ = P δ l δ...
of q ϕ {\displaystyle q_{\phi }} , which relates the ELBO to the Helmholtzfreeenergy. In the second line, ln p θ ( x ) {\displaystyle \ln p_{\theta...
functions in thermodynamics: Mass Energy (E) Enthalpy (H) Internal energy (U) Gibbs freeenergy (G) Helmholtzfreeenergy (F) Exergy (B) Entropy (S) Pressure...
Exergy Thermodynamic equations Thermodynamic potentials Gibbs freeenergyHelmholtzfreeenergy Crawford, F. H. (1963), pp. 106–107. Haase, R. (1971), pp...
times A has to be identified with F, another common symbol for Helmholtzfreeenergy. To prevent the need for this switch the following mnemonic is also...
potentials are the following functions: U Internal energy F Helmholtzfreeenergy H Enthalpy G Gibbs freeenergy Thermodynamic systems are typically affected...
and in the form of heat and light. Energy is a conserved quantity—the law of conservation of energy states that energy can be converted in form, but not...
derivation of the ideal-gas law, using the relationship between the Helmholtzfreeenergy and the partition function, but without using the equipartition...
the Helmholtzfreeenergy F as d F = − S d T − P d V {\displaystyle \mathrm {d} F=-S\,\mathrm {d} T-P\,\mathrm {d} V\,} and in terms of the Gibbs free energy...
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