Lesson 11 of 12 · 7 min
Gibbs energy and equilibrium
NCERT § "Gibbs Energy Change and Equilibrium"
ΔG° for burning methane is about −818 kJ mol⁻¹, and at 298 K that makes its equilibrium constant a number with over 140 digits. How does an energy turn into a K?
The lesson in notes
In short
At equilibrium ΔᵣG = 0, and the standard Gibbs energy change is related to the equilibrium constant by ΔᵣG° = −RT ln K = −2.303 RT log K.
A negative ΔᵣG° gives K > 1, favouring products; a positive ΔᵣG° gives K < 1, favouring reactants.
K = e^(−ΔᵣG°/RT); remember to express ΔᵣG° in J mol⁻¹ when R is 8.314 J K⁻¹ mol⁻¹.
ΔᵣG° can be found from ΔᵣH° − TΔᵣS°, so enthalpy and entropy data let you calculate K.
Strongly endothermic reactions can still reach a large K at high temperatures if ΔᵣS° is large and positive.
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Linking Gibbs energy to the equilibrium constant
The Organic Chemistry Tutor · English · Lecture · Open on YouTube