What this calculator does
Gibbs free energy works out reaction spontaneity from the change in enthalpy, entropy and temperature. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaΔG = ΔH − TΔS
The inputs explained
| Field | What to enter |
|---|---|
| Enthalpy change ΔH (kJ/mol) | A number, measured in kJ/mol. Starts at -92.4. |
| Entropy change ΔS (J/(mol·K)) | A number, measured in J/(mol·K). Starts at -198.4. |
| Temperature (K) | A number, measured in K. Starts at 298.15. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with enthalpy change δh
Every other input is held at the calculator’s starting values while enthalpy change δh varies. Select any row to load that scenario into the calculator.
How the answer changes with enthalpy change δh
| Enthalpy change ΔH (kJ/mol) | Gibbs free energy ΔG | T·ΔS term | Spontaneity |
|---|---|---|---|
| -46.2 | 12.953 kJ/mol | -59.153 kJ/mol | non-spontaneous at this temperature |
| -69.3 | -10.147 kJ/mol | -59.153 kJ/mol | spontaneous (favourable) at this temperature |
| -92.4 | -33.247 kJ/mol | -59.153 kJ/mol | spontaneous (favourable) at this temperature |
| -139 | -79.847 kJ/mol | -59.153 kJ/mol | spontaneous (favourable) at this temperature |
| -185 | -125.847 kJ/mol | -59.153 kJ/mol | spontaneous (favourable) at this temperature |
| -277 | -217.847 kJ/mol | -59.153 kJ/mol | spontaneous (favourable) at this temperature |