Gibbs Free Energy Formula |
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| \( G \;=\; H - T \cdot S \) | ||
| Symbol | English | Metric |
| \( G \) = Gibbs Ferr Energy | \(deg\) | \(rad\) |
| \( H \) = Enthalpy | \(Btu\;/\;lbm\) | \(kJ\;/\;kg\) |
| \( T_a \) = Absolute Temperature | \(R\) | \(K\) |
| \( S \) = Entropy | \(Btu \;/\; lbm-R\) | \(kJ \;/\; kg-K\) |
Gibbs free energy, abbreviated as \(G\), is a thermodynamic quantity that measures the amount of useful or available energy in a system that can be converted into work at constant temperature and pressure. It combines a system’s enthalpy, entropy, and temperature into a single value that predicts whether a process or chemical reaction will occur spontaneously. When a system undergoes a change, the sign of the change in Gibbs free energy determines its direction: a negative value indicates a spontaneous process, zero indicates equilibrium, and a positive value indicates a non-spontaneous process. Because of this predictive power, Gibbs free energy is one of the most important tools in chemistry, physics, and engineering for understanding reaction feasibility, phase changes, and energy efficiency in natural and industrial systems.
