Gibbs Energy & Spontaneity

Module 5 · 5 of 8

⚖️Gibbs Energy & Spontaneity

The single criterion for spontaneous change

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The single criterion for spontaneous change

Gibbs energy combines enthalpy and entropy into one number that decides direction at constant T and p: a process is spontaneous when ΔG < 0. The interplay of ΔH and ΔS even predicts the temperature where a reaction flips.

Difficulty

intermediate

Time

~35 min

Equations

Practice Qs

Learning Objectives

✓Use ΔG = ΔH − TΔS to judge spontaneity at constant T, p
✓Classify reactions by the signs of ΔH and ΔS (the four quadrants)
✓Find the crossover temperature where ΔG changes sign
✓Relate ΔG° to the equilibrium constant via ΔG° = −RT ln K
✓Distinguish ΔG (actual) from ΔG° (standard)

Prerequisites

Entropy & the second lawReaction enthalpy

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