Temperature, pressure, Kp and Le Chatelier’s principle

In a mixture of gases each gas has a partial pressure, and the total pressure is the sum of them, here in atm. For gas equilibria the concentrations can be replaced by partial pressures, and the constant is Kp, written exactly like Kc: for N₂ + 3H₂ ⇌ 2NH₃, Kp = P²(NH₃) ÷ (P(N₂) × P³(H₂)). At one temperature Kp does not change when the pressures change. Le Chatelier, a French scientist, summed up the shifts of an equilibrium: if a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that partly reduces the change. Adding a reactant, or removing a product, shifts it forward. Raising the pressure shifts it toward the side with fewer moles of gas, and nothing happens if both sides have the same number. Raising the temperature shifts it toward the endothermic direction, and lowering it toward the exothermic one. The word is “partly”: the change is reduced, never cancelled. For ammonia, 4 mol of gas (1 + 3) give 2 mol, so a higher pressure raises the yield of NH₃; it is the yield, not the speed, that the pressure argument is about.