Standard Entropy
What is Standard Entropy?
Standard entropy (S°) is the absolute entropy of one mole of a pure substance at standard conditions (298 K, 1 bar), measured in J mol⁻¹ K⁻¹. Unlike enthalpy, absolute entropies can be measured (starting from 0 at absolute zero — the third law of thermodynamics), and standard entropy values are tabulated for elements and compounds. The standard entropy change for a reaction is ΔS°rxn = Σ S°(products) − Σ S°(reactants), and combined with ΔH° it allows calculation of the Gibbs free energy change.
Key Facts
Frequently Asked Questions
Standard entropy (S°) is the absolute entropy of one mole of a pure substance at standard conditions (298 K, 1 bar), measured in J mol⁻¹ K⁻¹. Unlike enthalpy, absolute entropies can be measured (starting from 0 at absolute zero — the third law of thermodynamics), and standard entropy values are tabulated for elements and compounds. The standard entropy change for a reaction is ΔS°rxn = Σ S°(products) − Σ S°(reactants), and combined with ΔH° it allows calculation of the Gibbs free energy change.