Introduction

Le Chatelier's Principle is a fundamental concept in chemistry that helps predict how chemical systems at equilibrium respond to changes in their environment. This principle states:

"When a system at equilibrium experiences a change in conditions, the system will shift to counteract that change and establish a new equilibrium."

Factors Affecting Chemical Equilibrium

1. Concentration Changes

When the concentration of reactants or products changes, the system responds to minimize this change.

For a general equilibrium reaction: $A + B \rightleftharpoons C + D$

Key effects:

2. Pressure and Volume Changes

Pressure changes primarily affect reactions involving gases.

For a gaseous equilibrium: $2NO_2(g) \rightleftharpoons N_2O_4(g)$

Effects of pressure:

3. Temperature Changes

Temperature affects both reaction rates and equilibrium position.

For an exothermic reaction ($\Delta H < 0$):

For an endothermic reaction ($\Delta H > 0$):

4. Catalyst Effects

Catalysts affect reaction rates but not equilibrium position.

Key points:

Practical Examples

Example 1: Ammonia Synthesis

$N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) \quad \Delta H = -92\text{ kJ mol}^{-1}$

This industrial process demonstrates multiple aspects of Le Chatelier's Principle:

Example 2: Dinitrogen Tetroxide Equilibrium

$2NO_2(g) \rightleftharpoons N_2O_4(g) \quad \Delta H = -58\text{ kJ mol}^{-1}$

This reaction shows visible color changes with temperature: