Gibbs Free Energy Calculator

This calculator works out the Gibbs free energy change of a reaction, the single quantity that tells you whether it will happen spontaneously. In chemistry and thermodynamics, two factors compete to decide whether a reaction proceeds on its own: enthalpy, the heat it releases or absorbs, and entropy, the change in disorder. Gibbs free energy combines them, weighting entropy by temperature, into one number whose sign gives the answer. A negative Gibbs free energy change means the reaction is spontaneous and can proceed without outside energy; a positive value means it is non-spontaneous and needs energy to be driven; and zero means the system is at equilibrium. This makes it one of the most powerful ideas in chemistry, used to predict reactions, design processes, and understand everything from batteries to biology. This tool computes it. You enter the enthalpy change in kilojoules per mole, the temperature in kelvin, and the entropy change in joules per mole per kelvin, and the calculator returns the Gibbs free energy change in kilojoules per mole, states whether the reaction is spontaneous, shows the temperature-entropy term, and estimates the temperature at which the reaction would switch between spontaneous and not. The results update as you type, handling the unit difference between kilojoules for enthalpy and joules for entropy automatically. Use it for chemistry study, for predicting reaction spontaneity, or for thermodynamics problems. The relationship is Gibbs free energy change equals the enthalpy change minus the temperature times the entropy change. A key insight it reveals is the role of temperature: because entropy is multiplied by temperature, a reaction that is non-spontaneous when cold can become spontaneous when heated, or vice versa, which is why temperature so often determines whether a process runs.

ΔG = ΔH - T·ΔS, with ΔS converted from J to kJ. Negative ΔG is spontaneous; positive is non-spontaneous; zero is equilibrium. Rounded for display.