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Gibbs Free Energy - A Level Chemistry Definition

Reviewed by: Alexandra Brennan

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What is Gibbs Free Energy?

Gibbs free energy (G) is a thermodynamic function that determines whether a reaction is spontaneous under constant temperature and pressure.

It is given by the equation:

ΔG = ΔH - TΔS

  • ΔG is the Gibbs free energy change

  • ΔH is the enthalpy change

  • T is the temperature in Kelvin

  • ΔS is the entropy change.

A reaction is thermodynamically feasible if ΔG < 0 (negative), meaning it can occur without external energy input. Even if ΔG is negative, the reaction may still be slow due to a high activation energy. Understanding Gibbs free energy is essential in A Level Chemistry for predicting reaction feasibility and exploring entropy, enthalpy, and equilibrium concepts.

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Alexandra Brennan

Reviewer: Alexandra Brennan

Expertise: Chemistry

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

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