Effect of Pressure Changes on the Position of Equilibrium

Changes in pressure can also affect the position of equilibrium in reactions involving gases.

  • If there is an increase in pressure, the equilibrium will shift in the direction that produces the fewest molecules of gas. This will decrease the pressure.
  • If there is a decrease in pressure, the equilibrium will shift in the direction that produces the most molecules of gas. This will increase the pressure.

Example

For example, consider this reaction:

N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

  • On the left side of the equation, there are four molecules of gas.
  • On the right side of the equation, there are only two molecules of gas.

Therefore, an increase in pressure will shift the position of equilibrium to the right, producing more NH3. This will result in the fewest number of gas molecules. Conversely, a decrease in pressure will shift the equilibrium to the left, producing more N2 and 3H2, which have a greater number of gas molecules.