Le Chatelier's Principle

• Also known as the law of equilibrium, a central concept in chemical equilibria.
• If a system at equilibrium is disturbed, it shifts to oppose the change.
• Explains the qualitative effect of temperature, concentration, and pressure on gaseous equilibrium.
• Not applicable to solid reversible reactions (e.g., Fe(s) + S(s) → FeS(s)).
• Only temperature changes the equilibrium constant K.

Effect of Temperature on Solubility:

• Case I — Solubility decreases with temperature: CaSO₄, NaOH
• Case II — Solubility increases with temperature: most ionic salts (e.g., NaCl, KNO₃)

Effect of Pressure on Boiling & Freezing Point:

• The boiling point increases with an increase in pressure
• The freezing point increases with an increase in pressure (increased pressure → stronger molecular interaction → higher freezing point)