Thermodynamics Calculator (Gibbs Free Energy)

Gibbs Free Energy determines whether a chemical reaction will occur spontaneously — a foundational concept in chemistry, biochemistry, and engineering. Enter your Enthalpy Change (ΔH), Entropy Change (ΔS), and Temperature into the Gibbs Free Energy Calculator to get ΔG (kJ/mol), reaction spontaneity, and entropy contribution (−TΔS). Switch to equilibrium mode and provide an Equilibrium Constant (K) and Reaction Quotient (Q) to calculate Standard Gibbs Energy (ΔG°) instead.

Calculation Mode *

kJ/mol

Energy change at constant pressure

J/(mol·K)

Disorder change of the system

K

Used for equilibrium-based calculations

Current state of reaction relative to equilibrium

Results

Gibbs Free Energy (ΔG)

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Reaction Spontaneity

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Standard Gibbs Energy (ΔG°)

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Entropy Contribution (-TΔS)

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Frequently Asked Questions

How do I calculate Gibbs free energy?

Gibbs free energy is calculated using ΔG = ΔH - TΔS, where ΔH is enthalpy change, T is absolute temperature in Kelvin, and ΔS is entropy change. Make sure units are consistent (convert J to kJ if needed).

Why is Gibbs free energy 0 at equilibrium?

At equilibrium, there's no net change in the system and no driving force for the reaction to proceed in either direction. This corresponds to ΔG = 0, representing a balanced state between forward and reverse reactions.

What information does Gibbs free energy give about a reaction?

Gibbs free energy predicts reaction spontaneity: ΔG < 0 means spontaneous (favorable), ΔG > 0 means non-spontaneous (requires energy input), and ΔG = 0 indicates equilibrium.

How to determine if a reaction is spontaneous or nonspontaneous?

Check the sign of ΔG: negative values indicate spontaneous reactions that can occur naturally, while positive values indicate non-spontaneous reactions requiring external energy input to proceed.

What's the difference between ΔG and ΔG°?

ΔG° is the standard Gibbs free energy change under standard conditions (1 atm, 25°C), while ΔG accounts for actual reaction conditions including temperature and concentrations of reactants and products.

Why must temperature be in Kelvin for Gibbs energy calculations?

The Gibbs free energy equation is derived from thermodynamic principles that require absolute temperature. Kelvin is the absolute temperature scale starting at absolute zero, ensuring accurate calculations.