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The relationship between the standard Gibbs free energy change Δ r G o and chemical equilibrium is revealing. This relationship is defined by the equation Δ r G o = -RT ln(K), where K is the equilibrium constant, which is equal to the reaction quotient Q in equilibrium.
In thermodynamics, the Gibbs free energy (or Gibbs energy as the recommended name; symbol ) is a thermodynamic potential that can be used to calculate the maximum amount of work, other than pressure–volume work, that may be performed by a thermodynamically closed system at constant temperature and pressure.
The Hammett equation predicts the equilibrium constant or reaction rate of a reaction from a substituent constant and a reaction type constant. The Edwards equation relates the nucleophilic power to polarisability and basicity. The Marcus equation is an example of a quadratic free-energy relationship (QFER). [citation needed]
An equilibrium constant is related to the standard Gibbs free energy change of reaction by Δ G ⊖ = − R T ln K ⊖ , {\displaystyle \Delta G^{\ominus }=-RT\ln K^{\ominus },} where R is the universal gas constant , T is the absolute temperature (in kelvins ), and ln is the natural logarithm .
The standard Gibbs energy change, together with the Gibbs energy of mixing, determine the equilibrium state. [8] [9] In this article only the constant pressure case is considered. The relation between the Gibbs free energy and the equilibrium constant can be found by considering chemical potentials. [1]
An equilibrium constant is related to the standard Gibbs free energy change for the reaction = R is the gas constant and T is the absolute temperature. At 25 °C, ΔG ⊖ = (−5.708 kJ mol −1) ⋅ log β. Free energy is made up of an enthalpy term and an entropy term.
This equation is exact at any one temperature and all pressures, derived from the requirement that the Gibbs free energy of reaction be stationary in a state of chemical equilibrium. In practice, the equation is often integrated between two temperatures under the assumption that the standard reaction enthalpy is constant (and furthermore, this ...
which relates the Gibbs energy to a chemical equilibrium constant, the van 't Hoff equation can be derived. [ 9 ] Since the change in a system's Gibbs energy is equal to the maximum amount of non-expansion work that the system can do in a process, the Gibbs-Helmholtz equation may be used to estimate how much non-expansion work can be done by a ...