Gibbs free energy

In thermodynamics the Gibbs free energy is a state function of any system defined as

Related Topics:
Thermodynamics - State function

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:G = H − T·S

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where

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:G is the Gibbs free energy, measured in joules

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:H is the enthalpy, measured in joules

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:T is the temperature, measured in kelvins

Related Topics:
Temperature - Kelvin

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:S is the entropy, measured in joules per kelvin

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Each unit in the equation above can be divided by the amount of substance, measured in moles, to form molar Gibbs free energy.

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The Gibbs free energy is one of the most important thermodynamic functions for the characterization of a system. It determines outcomes such as the voltage of an electrochemical cell, and the equilibrium constant for a reversible reaction. Gibbs free energy also determines how much work is attainable for any given reversible process at constant temperature and pressure. The analogous thermodynamic function at constant temperature and volume, is the Helmholtz free energy.

Related Topics:
Voltage - Electrochemical cell - Equilibrium constant - Reversible reaction - Temperature - Pressure - Volume - Helmholtz free energy

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Any natural process occurs spontaneously if and only if the associated change in G for the system is negative (Delta G < 0). Likewise, a system reaches equilibrium when the associated change in G for the system is zero (Delta G = zero), and no spontaneous process will occur if the change in G is positive (Delta G > 0).

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It is named after American physicist Willard Gibbs.

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