Gibbs Free Energy Calculator

Gibbs free energy (G) is a thermodynamic potential that measures the maximum useful work a system can do at constant temperature and pressure. The change in Gibbs free energy (delta G = delta H - T * delta S) tells us whether a reaction is spontaneous. If delta G is negative, the reaction proceeds spontaneously; if positive, it is non-spontaneous; if zero, the system is at equilibrium.

delta H negative (exothermic) favors spontaneity. delta S positive (entropy increase, more disorder) favors spontaneity. At any temperature, the sign of delta G determines spontaneity: delta G = delta H - T*delta S. A negative delta H and positive delta S always give delta G negative (always spontaneous).

At equilibrium, delta G = 0, so delta G_standard = -R*T*ln(K), where K is the equilibrium constant. Rearranging: K = exp(-delta G_standard / (R*T)). A strongly negative standard Gibbs energy means K >> 1 (products heavily favored at equilibrium). A positive standard Gibbs energy means K << 1 (reactants favored).

Delta G_standard (delta G°) is measured at standard conditions (25 degC, 1 atm, 1 M concentrations). Delta G accounts for actual reaction conditions: delta G = delta G° + R*T*ln(Q), where Q is the reaction quotient. When Q < K, delta G is negative and the reaction proceeds forward toward equilibrium.

Yes. Non-spontaneous reactions can be driven by coupling them to spontaneous processes that supply enough energy. For example, ATP hydrolysis (delta G = -30 kJ/mol) drives many biosynthetic reactions in cells. Electrolysis uses electrical energy to drive non-spontaneous electrochemical reactions. Photosynthesis uses light energy to convert CO2 and water into glucose.