The magnitude of the depletion force, \ mathcal { F } is equal to the change in Helmholtz free energy with distance between two large spheres and is given by
22.
In thermodynamics, the "'Helmholtz free energy "'is a thermodynamic potential that measures the useful closed thermodynamic system at a constant temperature and volume.
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However, the complexity term of variational free energy shares the same fixed point as Helmholtz free energy ( under the assumption the system is thermodynamically closed but not isolated ).
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In statistical mechanics, the relationship between the Helmholtz free energy and the partition function is fundamental, and is used to calculate the thermodynamic properties of matter; see configuration integral for more details.
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The Helmholtz free energy is often the most useful thermodynamic potential when temperature and volume are held constant, while the Gibbs energy is often the most useful when temperature and pressure are held constant.
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For example, the Gibbs free energy is used when considering processes that occur under constant pressure and temperature conditions whereas the Helmholtz free energy is used when considering processes that occur under constant volume and temperature conditions.
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The system's properties are then most conveniently described using the thermodynamic potential Helmholtz free energy ( " A " = " U "-" TS " ), a Legendre transformation of the energy.
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In physics, " free energy " most often refers to the Helmholtz free energy, denoted by " A ", while in chemistry, " free energy " most often refers to the Gibbs free energy.
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By making further Legendre transformations from " U " to other thermodynamic potentials like the Enthalpy H = U + PV and Helmholtz free energy F = U-TS, expressions for the chemical potential may be obtained in terms of these:
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The Helmholtz free energy was developed by Hermann von Helmholtz, a German physicist, and is usually denoted by the letter " A " ( from the German Arbeit or work ), or the letter " F ".
