Gibbs Free Energy with Equilibrium Constant ('K_eq')

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Equation / Last modified by smcmstudent on 2017/06/15 21:21
`Delta G = `
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The Gibbs Free Energy of reaction formula, `Delta G=-R * T * ln (K_a)`, calculates the process-initiating work available to trigger a reaction.  As such it is defined in units of energy / amount of substance (J/mol).

`Delta G=-R * T * ln (K_a)`

  • R is the ideal gas constant (8.314 J/mol*K)
  • T is temperature (Kelvin)
  • `K_a` is the acid equilibrium constant (unit-less)
  • ΔG is the Gibbs free energy (J/mol)


There are several variations of the Gibbs Free Energy equation, however, this equation calculates ΔG at standard pressure. Gibbs energy, ΔG, is defined as the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature.  The Gibbs Free Energy in this definition is the state in which a process can occur while maintaining constant pressure and temperature. Understanding the free energy of a reaction allows one to determine under what conditions a chemical or biological reaction will proceed, the state of equilibrium and how to compute the equilibrium constant Keq of the reaction.

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Whitten, et al. "Chemistry" 10th Edition. Pp. 696


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