Gibbs Free Energy with Equilibrium Constant ('K_eq')

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Equation / Last modified by KurtHeckman on 2019/04/22 23:29
`Delta G = `
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The Gibbs Free Energy calculator computes the free energy based on the temperature, equilibrium constant and the Gas Law constant (R).

INSTRUCTIONS: Choose units and enter the following:

  • (T) This is the temperature
  • (Ka) This is the equilibrium constant

Gibbs Free Energy (ΔG): The calculator returns the energy in Joules per mole.  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The Gibbs Free Energy of reaction formula,  ΔG = -R • T • ln (Ka) , calculates the process-initiating work available to trigger a reaction.  As such it is defined in units of energy / amount of substance (J/mol).

     ΔG = -R • T • ln (Ka)


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


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.

Related Topics

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


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