IB Chemistry Topic R1.4.4 Gibbs Free Energy and Equilibrium Revision Notes (HL)

IB Chemistry Topic R1.4.4 Gibbs Free Energy and Equilibrium Revision Notes (HL) | RevisionDojo

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Gibbs Free Energy, Equilibrium, and Spontaneity

$ΔG$ and Reaction Progress

As discussed in the previous sections, Gibbs free energy ($ \Delta G $) is a thermodynamic quantity that helps us predict whether a reaction is spontaneous under constant pressure and temperature.
A reaction is spontaneous if $ \Delta G $ is negative, meaning it can proceed without external energy input.
However, as a reaction progresses, the concentrations of reactants and products change, and so does $ \Delta G $.
At the start of a reaction, $ \Delta G $ is often negative, favoring the forward reaction.
As the reaction progresses, $ \Delta G $ becomes less negative as the system approaches equilibrium.
At equilibrium, $ \Delta G = 0 $. At this point, there is no net change in the concentrations of reactants and products because the forward and reverse reactions occur at the same rate.

Example

Consider the Haber process: $$ \text{N}_2(g) + 3\text{H}_2(g) \leftrightharpoons 2\text{NH}_3(g) $$
Initially, $ \Delta G $ is negative, so the formation of ammonia ($ \text{NH}_3 $) is spontaneous.
As more ammonia is produced, $ \Delta G $ becomes less negative until equilibrium is reached, at which point $ \Delta G = 0 $.

Note

At equilibrium, the system’s Gibbs free energy is at its minimum, representing a state of maximum stability.

The Relationship Between ΔG and the Equilibrium Constant (K)

At equilibrium, the concentrations of products and reactants form a constant ratio, defined as the equilibrium constant ($ K $).
The relationship between $ \Delta G $ and $ K $ is expressed by the equation: $$ \Delta G^\circ = -RT \ln K $$ where:
1. $ \Delta G^\circ $: Standard Gibbs free energy change ($kJ \, mol^{-1}$) under standard conditions.
2. $ R $: Gas constant ($ 8.31 \, \text{J mol}^{-1} \, \text{K}^{-1} $).
3. $ T $: Temperature in Kelvin (K).

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Gibbs Free Energy, Equilibrium, and Spontaneity

$ΔG$ and Reaction Progress

As discussed in the previous sections, Gibbs free energy ($ \Delta G $) is a thermodynamic quantity that helps us predict whether a reaction is spontaneous under constant pressure and temperature.
A reaction is spontaneous if $ \Delta G $ is negative, meaning it can proceed without external energy input.
However, as a reaction progresses, the concentrations of reactants and products change, and so does $ \Delta G $.
At the start of a reaction, $ \Delta G $ is often negative, favoring the forward reaction.
As the reaction progresses, $ \Delta G $ becomes less negative as the system approaches equilibrium.
At equilibrium, $ \Delta G = 0 $. At this point, there is no net change in the concentrations of reactants and products because the forward and reverse reactions occur at the same rate.

Example

Consider the Haber process: $$ \text{N}_2(g) + 3\text{H}_2(g) \leftrightharpoons 2\text{NH}_3(g) $$
Initially, $ \Delta G $ is negative, so the formation of ammonia ($ \text{NH}_3 $) is spontaneous.
As more ammonia is produced, $ \Delta G $ becomes less negative until equilibrium is reached, at which point $ \Delta G = 0 $.

Note

At equilibrium, the system’s Gibbs free energy is at its minimum, representing a state of maximum stability.

The Relationship Between ΔG and the Equilibrium Constant (K)

At equilibrium, the concentrations of products and reactants form a constant ratio, defined as the equilibrium constant ($ K $).
The relationship between $ \Delta G $ and $ K $ is expressed by the equation: $$ \Delta G^\circ = -RT \ln K $$ where:
1. $ \Delta G^\circ $: Standard Gibbs free energy change ($kJ \, mol^{-1}$) under standard conditions.
2. $ R $: Gas constant ($ 8.31 \, \text{J mol}^{-1} \, \text{K}^{-1} $).
3. $ T $: Temperature in Kelvin (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 R1.4.4 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

Gibbs Free Energy, Equilibrium, and Spontaneity

$ΔG$ and Reaction Progress

The Relationship Between ΔG and the Equilibrium Constant (K)

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Gibbs Free Energy, Equilibrium, and Spontaneity

$ΔG$ and Reaction Progress

The Relationship Between ΔG and the Equilibrium Constant (K)

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Duis aute irure dolor in reprehenderit

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