How does pressure affect equilibrium?

Pressure affects equilibrium mainly in reactions involving gases, according to Le Chatelier’s Principle.

Key points:

1. Increase in pressure:
   • The system shifts toward the side with fewer gas molecules to reduce the pressure.
2. Decrease in pressure:
   • The system shifts toward the side with more gas molecules to increase the pressure.
3. No effect if gas molecules are equal:
   • If the number of gas molecules is the same on both sides of the reaction, changing pressure does not shift the equilibrium.
4. Effect on equilibrium constant (K):
   • Pressure changes do not change K; they only shift the position of equilibrium.

Example: For the Haber process:

• N₂ + 3H₂ ⇌ 2NH₃
• Increasing pressure favors the formation of NH₃ (fewer gas molecules).

In simple terms: the system “adjusts” to minimize pressure changes by favoring the side with fewer or more gas molecules as needed.