Gibbs Free Energy Calculator

Gibbs free energy (ΔG) integrates the first and second laws of thermodynamics into a single state function. The standard governing equation is ΔG = ΔH - TΔS, where ΔH represents enthalpy change, T is absolute temperature in Kelvin, and ΔS represents entropy change. Because laboratory temperatures are typically measured in Celsius, our calculator automatically converts Celsius to Kelvin by adding 273.15. A negative ΔG value indicates a spontaneous process, a positive value points to a nonspontaneous process, and zero signifies chemical equilibrium.

Imagine you are analyzing a chemical reaction running at 25°C (which equals 298.15 K). Let us assume the enthalpy change (ΔH) is -50 kJ/mol, and the entropy change (ΔS) is -0.1 kJ/(mol·K). First, compute the temperature-entropy component: 298.15 K × -0.1 kJ/(mol·K) = -29.815 kJ/mol. Next, apply the main formula: ΔG = -50 - (-29.815) = -50 + 29.815 = -20.185 kJ/mol. Because the resulting Gibbs free energy is negative (-20.185 kJ/mol), the reaction is spontaneous at this temperature.

Always double-check your units before inputting values; enthalpy is commonly given in kilojoules per mole (kJ/mol), while entropy is frequently reported in joules per mole-Kelvin (J/(mol·K)). Ensure you convert entropy to kilojoules if your enthalpy is in kilojoules to prevent magnitude mismatch errors. Remember that temperature must always be entered as an absolute value in Kelvin for thermodynamic equations to yield correct physical insights.