Gibbs Free Energy Calculator Formula

Understand the math behind the gibbs free energy calculator. Each variable explained with a worked example.

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Formulas Used

Gibbs Free Energy (ΔG)

delta_g = delta_h - (temp * delta_s / 1000)

Variables

VariableDescriptionDefault
delta_hEnthalpy Change (ΔH)(kJ)-100
delta_sEntropy Change (ΔS)(J/K)-50
tempTemperature (T)(K)298

How It Works

Gibbs Free Energy

Formula

ΔG = ΔH − TΔS

Where:

  • ΔG = Gibbs free energy change (kJ)
  • ΔH = enthalpy change (kJ)
  • T = temperature (K)
  • ΔS = entropy change (J/K, converted to kJ/K by dividing by 1000)

    • If ΔG < 0, the reaction is spontaneous. If ΔG > 0, it is non-spontaneous. If ΔG = 0, the system is at equilibrium.

    Worked Example

    A reaction with ΔH = -100 kJ and ΔS = -50 J/K at 298 K.

    delta_h = -100delta_s = -50temp = 298
    1. 01ΔG = ΔH - TΔS
    2. 02ΔG = -100 - (298 × (-50)/1000)
    3. 03ΔG = -100 - (-14.9)
    4. 04ΔG = -100 + 14.9
    5. 05ΔG = -85.1 kJ (spontaneous)

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