Effects of Pressure on the position of Equilibrium

Pressure only affects equilibria that involve gases. By Le Chatelier's principle, if the pressure is increased the position of equilibrium shifts towards the side with fewer moles of gas, to reduce the pressure.If the pressure is decreased, the position of equilibrium shifts towards the side with more moles of gas, to increase the pressure.For N₂(g) + 3H₂(g) ⇌ 2NH₃(g) there are 4 moles of gas on the left and 2 on the right, so a higher pressure moves the equilibrium to the right and increases the yield of ammonia.If both sides have the same number of moles of gas, as in H₂(g) + I₂(g) ⇌ 2HI(g), changing the pressure has no effect on the position of equilibrium.A higher pressure also increases the rate, because gas molecules are closer together and collide more often.