23.4.1—The Gibbs equation ΔG
- Syllabus
- 9701–2028–2029
- Objective
- 23.4.1
- Level
- A2
Use Gibbs free energy to combine enthalpy and entropy effects
The standard Gibbs equation is ΔG° = ΔH° − TΔS°, where temperature is in kelvin and ΔH° and TΔS° use the same energy units.
Enthalpy favours exothermic change, while the entropy term becomes more influential as temperature increases. The equation combines these competing contributions for a specified standard state.
An endothermic reaction can still have negative ΔG° at high T if its positive ΔS° makes TΔS° larger than ΔH°.
Do not insert Celsius or combine kJ enthalpy with J entropy without conversion.
ConceptA-Level CAIE Chemistry A2