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Which expression correctly relates the Gibbs free energy change for a reaction to its equilibrium constant Kc?

1. −ΔG = RT ln Kc
2. ΔG° = RT ln Kc
3. −ΔG° = RT ln Kc
4. ΔG = RT ln Kc

Correct answer: −ΔG° = RT ln Kc

Solution

The correct thermodynamic relation uses the standard free energy: delta G(standard) = -RT ln Kc, equivalently -delta G(standard) = RT ln Kc.

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