Le Châtelier's Principle

Le Châtelier's Principle

1. Definition

• Le Châtelier's Principle states: When a system at equilibrium is disturbed, it will shift to counteract the change and restore equilibrium.
• This applies to changes in temperature, concentration, or pressure in a closed system.

2. How Equilibrium Adjusts

When a factor changes:

✔ The equilibrium position is disturbed.

✔ The forward or reverse reaction is favoured.

✔ The system opposes the applied change.

✔ The reaction rate changes.

✔ A new equilibrium is established where the forward and reverse reactions occur at equal rates again.

3. Applying Le Châtelier's Principle to Changes in Equilibrium Conditions

3.1 Temperature Changes $(\Delta T)$

• Increasing temperature shifts equilibrium towards the endothermic reaction.
• Decreasing temperature shifts equilibrium towards the exothermic reaction.

3.2 Concentration Changes $(\Delta c)$

• Increasing reactant concentration → Shifts equilibrium towards the products.
• Increasing product concentration → Shifts equilibrium towards the reactants.
• Removing a substance causes equilibrium to shift to replace what was removed.

3.3 Pressure Changes $(\Delta p)$ (For gaseous reactions only)

• Increasing pressure → Equilibrium shifts to the side with fewer gas molecules.
• Decreasing pressure → Equilibrium shifts to the side with more gas molecules.

3.4 Effect of a Catalyst

• Speeds up both forward and reverse reactions equally.
• Does NOT shift equilibrium but helps reach equilibrium faster.

4. Steps to Predict Equilibrium Shifts

1. Check if the reaction is reversible $(\leftrightarrow).$
2. Balance the equation and count gas molecules on both sides.
3. Determine the type of reaction (exothermic or endothermic).
4. Identify the change (temperature, pressure, concentration).
5. Apply Le Châtelier's Principle to predict the direction of the shift.
6. Describe how the concentrations of reactants and products change.