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.
Practice With the Free Calculators
Reading the method is step one — running real numbers through it is what makes it stick. These free tools pair well with this guide: