IB Chemistry Topic R1.4.3 Spontaneity and Gibbs Free Energy Revision Notes (HL)

IB Chemistry Topic R1.4.3 Spontaneity and Gibbs Free Energy Revision Notes (HL) | RevisionDojo

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Spontaneity: Why a Negative ΔG Lets a Reaction Proceed

What Makes a Process Spontaneous?

Definition

Spontaneity

A chemical reaction or physical process is spontaneous if it occurs without external intervention under a given set of conditions.

A spontaneous change proceeds on its own, without a continuous input of external energy.
Spontaneity is decided by the sign of the Gibbs free energy change, $\Delta G = \Delta H - T\Delta S$, introduced in R1.4.2.

Reading the Sign of ΔG

$\Delta G < 0$: the reaction is spontaneous.
$\Delta G = 0$: the system is at equilibrium.
$\Delta G > 0$: the reaction is non-spontaneous under the given conditions.

Example

The combustion of methane, $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$, is strongly exothermic ($\Delta H < 0$).
It also increases disorder ($\Delta S > 0$).
Both terms make $\Delta G$ negative, so the reaction is spontaneous at all temperatures.

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Spontaneity: Why a Negative ΔG Lets a Reaction Proceed

What Makes a Process Spontaneous?

Definition

Spontaneity

A chemical reaction or physical process is spontaneous if it occurs without external intervention under a given set of conditions.

A spontaneous change proceeds on its own, without a continuous input of external energy.
Spontaneity is decided by the sign of the Gibbs free energy change, $\Delta G = \Delta H - T\Delta S$, introduced in R1.4.2.

Reading the Sign of ΔG

$\Delta G < 0$: the reaction is spontaneous.
$\Delta G = 0$: the system is at equilibrium.
$\Delta G > 0$: the reaction is non-spontaneous under the given conditions.

Example

The combustion of methane, $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$, is strongly exothermic ($\Delta H < 0$).
It also increases disorder ($\Delta S > 0$).
Both terms make $\Delta G$ negative, so the reaction is spontaneous at all temperatures.

Definition

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Note

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Excepteur sint occaecat cupidatat non proident

Tip

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Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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 R1.4.3 Spontaneity and Gibbs Free Energy 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

Spontaneity: Why a Negative ΔG Lets a Reaction Proceed

What Makes a Process Spontaneous?

Reading the Sign of ΔG

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Spontaneity: Why a Negative ΔG Lets a Reaction Proceed

What Makes a Process Spontaneous?

Reading the Sign of ΔG

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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