IB Chemistry Topic R2.3.4 Le Châtelier’s Principle Revision Notes (SL/HL)

IB Chemistry Topic R2.3.4 Le Châtelier’s Principle Revision Notes (SL/HL) | RevisionDojo

Written by official IB examiners

Le Châtelier's Principle and Its Applications

Analogy

Consider that you’re sitting in a crowded room when someone opens a window, letting in a cold draft.
You might instinctively reach for a jacket or move to a warmer spot to counteract the chill.
This natural response to restore comfort mirrors how chemical systems respond to disturbances.

When a system at equilibrium experiences a change in concentration, pressure, or temperature, it adjusts to minimize the disturbance and reestablish equilibrium.

The Principle: Systems Resist Change

Definition

Le Châtelier's Principle

Le Châtelier's Principle states:

"If a dynamic equilibrium is disturbed by a change in the reaction conditions, the system adjusts to counteract the disturbance and restore a new equilibrium."

The “disturbances” can include:

Concentration changes: Adding or removing reactants or products.
Pressure changes: Altering the volume or overall pressure in systems involving gases.
Temperature changes: Heating or cooling the system.

Effect of Concentration Changes

How Does Concentration Affect Equilibrium?

When the concentration of a reactant or product changes, the system shifts to reduce the impact of this disturbance.

Adding Reactants: The system shifts toward the products to consume the excess reactants.
Removing Reactants: The system shifts toward the reactants to replenish the loss.
Adding Products: The system shifts toward the reactants to reduce the excess products.
Removing Products: The system shifts toward the products to compensate for the removal.

Example

Consider the synthesis of ammonia: $$
\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)
$$
At equilibrium, if more hydrogen ($\text{H}_2$) is added, the forward reaction is favored, producing more ammonia ($\text{NH}_3$) to counteract the disturbance.
The equilibrium shifts to the right.

Common Mistake

Many students incorrectly assume that adding more of a substance will always increase its equilibrium concentration.
Remember, the system adjusts to partially counteract the change, so the final concentration may still differ from the initial equilibrium state.

Effect of Pressure Changes

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Le Châtelier's Principle and Its Applications

Analogy

Consider that you’re sitting in a crowded room when someone opens a window, letting in a cold draft.
You might instinctively reach for a jacket or move to a warmer spot to counteract the chill.
This natural response to restore comfort mirrors how chemical systems respond to disturbances.

When a system at equilibrium experiences a change in concentration, pressure, or temperature, it adjusts to minimize the disturbance and reestablish equilibrium.

The Principle: Systems Resist Change

Definition

Le Châtelier's Principle

Le Châtelier's Principle states:

"If a dynamic equilibrium is disturbed by a change in the reaction conditions, the system adjusts to counteract the disturbance and restore a new equilibrium."

The “disturbances” can include:

Concentration changes: Adding or removing reactants or products.
Pressure changes: Altering the volume or overall pressure in systems involving gases.
Temperature changes: Heating or cooling the system.

Effect of Concentration Changes

How Does Concentration Affect Equilibrium?

When the concentration of a reactant or product changes, the system shifts to reduce the impact of this disturbance.

Adding Reactants: The system shifts toward the products to consume the excess reactants.
Removing Reactants: The system shifts toward the reactants to replenish the loss.
Adding Products: The system shifts toward the reactants to reduce the excess products.
Removing Products: The system shifts toward the products to compensate for the removal.

Example

Consider the synthesis of ammonia: $$
\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)
$$
At equilibrium, if more hydrogen ($\text{H}_2$) is added, the forward reaction is favored, producing more ammonia ($\text{NH}_3$) to counteract the disturbance.
The equilibrium shifts to the right.

Common Mistake

Many students incorrectly assume that adding more of a substance will always increase its equilibrium concentration.
Remember, the system adjusts to partially counteract the change, so the final concentration may still differ from the initial equilibrium state.

Effect of Pressure Changes

Definition

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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 R2.3.4 Le Châtelier’s Principle 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

Le Châtelier's Principle and Its Applications

The Principle: Systems Resist Change

Effect of Concentration Changes

How Does Concentration Affect Equilibrium?

Effect of Pressure Changes

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Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Le Châtelier's Principle and Its Applications

The Principle: Systems Resist Change

Effect of Concentration Changes

How Does Concentration Affect Equilibrium?

Effect of Pressure Changes

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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