IB Chemistry Topic R2.3.7 Gibbs Free Energy and Equilibrium Revision Notes (HL)

IB Chemistry Topic R2.3.7 Gibbs Free Energy and Equilibrium Revision Notes (HL) | RevisionDojo

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Standard Gibbs Free Energy Change ($ \Delta G^\circ $) and Its Significance

As discussed in Reactivity 1.4, the Gibbs free energy change ($ \Delta G $) is a thermodynamic quantity that determines whether a reaction is spontaneous.
A spontaneous reaction proceeds without requiring external energy input.
1. $ \Delta G< 0 $: The reaction is spontaneous in the forward direction.
2. $ \Delta G >0 $: The reaction is non-spontaneous in the forward direction (but spontaneous in reverse).
3. $ \Delta G = 0 $: The system is at equilibrium.

Note

When we discuss $ \Delta G^\circ $, we refer to the Gibbs free energy change under standard conditions: 1 atm pressure for gases, 1 $\mathrm{mol \, dm^{-3}}$ concentration for solutions, and a specified temperature (usually 298 K unless otherwise stated).

But how does $ \Delta G^\circ $ relate to the equilibrium constant ($ K $)?

The Equation Relating $ \Delta G^\circ $ and $ K $

The connection between $ \Delta G^\circ $ and $ K $ is expressed mathematically as: $$
\Delta G^\circ = -RT \ln K
$$ where:
1. $ \Delta G^\circ $: Standard Gibbs free energy change (in $\text{J mol}^{-1}$).
2. $ R $: Gas constant ($ 8.31 \, \mathrm{J \, mol^{-1} \, K^{-1}} $).
3. $ T $: Absolute temperature in Kelvin.
4. $ K $: Equilibrium constant (unitless).
This equation links thermodynamics ($ \Delta G^\circ $) to equilibrium ($ K $) and provides critical insights into reaction behavior:

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IB Chemistry R2.3.7 Gibbs Free Energy and Equilibrium Notes

Standard Gibbs Free Energy Change ($ \Delta G^\circ $) and Its Significance

The Equation Relating $ \Delta G^\circ $ and $ K $

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Standard Gibbs Free Energy Change ($ \Delta G^\circ $) and Its Significance

The Equation Relating $ \Delta G^\circ $ and $ K $

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry R2.3.7 Gibbs Free Energy and Equilibrium Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

Standard Gibbs Free Energy Change ($ \Delta G^\circ $) and Its Significance

The Equation Relating $ \Delta G^\circ $ and $ K $

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Standard Gibbs Free Energy Change ($ \Delta G^\circ $) and Its Significance

The Equation Relating $ \Delta G^\circ $ and $ K $

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