Gibbs Free Energy Explained
Chemistry Tools | March 10, 2026 | 8 min read
What delta G means, how spontaneity works, and how enthalpy and entropy compete.
| delta G | Meaning | Interpretation |
| Negative | Product-favored | Spontaneous as written |
| Positive | Reactant-favored | Nonspontaneous as written |
| Zero | Balanced | Equilibrium |
What Gibbs Free Energy Measures
Gibbs free energy predicts whether a process is thermodynamically favorable at constant temperature and pressure. It combines heat change, entropy change, and temperature into one value: delta G.
A negative delta G means the process is spontaneous as written. A positive delta G means it is not spontaneous as written. Delta G equal to zero means the system is at equilibrium.
Enthalpy and Entropy
Delta H measures heat flow. Exothermic processes have negative delta H and often help make delta G negative. Delta S measures disorder or energy dispersal. Positive delta S also helps make delta G negative because the term -T delta S becomes negative.
Temperature matters because entropy is multiplied by T. A reaction with positive delta H and positive delta S may become favorable at high temperature, while a reaction with negative delta H and negative delta S may only be favorable at low temperature.
How To Use the Equation
Keep units consistent. If delta H is in kJ/mol, convert delta S from J/mol K to kJ/mol K before multiplying by temperature. Use kelvin, not Celsius.
After calculating, interpret the sign before worrying about the exact number. The sign answers spontaneity, and the magnitude gives a sense of thermodynamic driving force.
Useful Site Tools
The Gibbs Free Energy Calculator can solve delta G problems and interpret spontaneity. Pair it with the blog article when you need the concept, and use the calculator when you need fast arithmetic.