Advanced Topic 479 of 1102 Kinetics & Equilibrium
Equilibrium and Free Energy
Standard Gibbs energy change equals minus RT ln K.
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In-depth explanation of Equilibrium and Free Energy
The standard Gibbs free energy change of a reaction is related to its equilibrium constant by delta G standard = -RT ln K, where R is the gas constant and T is the absolute temperature. A negative standard free energy change corresponds to K greater than one, which means products are favoured at equilibrium, while a positive value corresponds to K less than one. This connection links the thermodynamic driving force of a reaction to the composition it reaches at equilibrium. The temperature dependence of K follows from the standard enthalpy and entropy changes through delta G = delta H - T delta S.
Going deeper: Equilibrium and Free Energy
Key ideas: Use delta G standard = -RT ln K, with R = 8.314 J per mol per K, so at 298 K, K = exp(-delta G standard / 2478) with delta G in J per mol. Away from standard conditions use delta G = delta G standard + RT ln Q, which is zero at equilibrium. Combine with delta G = delta H - T delta S to estimate K at other temperatures.
Common mistakes and connections: Students confuse delta G standard with delta G. The first fixes K, while the second sets the direction at the current composition. Another error is neglecting to convert kJ to J when using R. A positive delta G standard does not mean no reaction occurs, only that K is below 1. Connects the thermodynamics area to the van't Hoff equation and to electrochemistry via delta G = -nFE.
Visualization of Equilibrium and Free Energy
delta G = -RT ln K: a free energy of -11.4 kJ/mol gives log K = 2 (K = 100), and every 5.7 kJ/mol changes K tenfold at 298 K. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A reaction with delta G standard = -11.4 kJ per mol at 298 K has K of about 100.
Frequently asked questions about Equilibrium and Free Energy
What is Equilibrium and Free Energy?
Standard Gibbs energy change equals minus RT ln K.
Is Equilibrium and Free Energy a beginner, intermediate or advanced topic?
Equilibrium and Free Energy is a advanced topic in Kinetics & Equilibrium. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Equilibrium and Free Energy?
Study these earlier topics in Kinetics & Equilibrium first: Haber Process, Contact Process, Ostwald Process.
What comes after Equilibrium and Free Energy?
The next topics in Kinetics & Equilibrium are Solubility Product and Common Ion Effect.
Can I practise Equilibrium and Free Energy with quizzes?
Yes. The interactive lesson includes a self-check question on Equilibrium and Free Energy, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Equilibrium and Free Energy fits in Kinetics & Equilibrium
Equilibrium and Free Energy is topic 60 of 91 in Kinetics & Equilibrium.