How much the forward or reverse reaction is favored at equilibrium can be found by comparing the amounts of reactants to products at the point of equilibrium.
As the partial pressures of a gas in a closed system are directly linked to the moles of that gas, partial pressures of reactants and products can be used to determine how much the forward or reverse reaction is favoured.
The equilibrium constant, Kp, describes the ratio of reactants compared to products. It is found by dividing the partial pressures of all products by the partial pressures of all reactants (raised to the power of their molar ratios).
Equilibrium Constant, Kp
The equilibrium constant, Kc, is a constant used to describe how much an equilibrium favours the forward and backward reactions in an equilibrium.
The equilibrium constant, Kp, works in a similar way to Kc and is also used to describe how much an equilibrium favours the forward and backward reaction. The key difference is that Kc uses molar concentrations (mol dm ) whereas Kp uses partial pressures.
For the following reaction:
By taking known moles of gases and the total pressure of a system, Kp can be found for a particular reversible reaction.
Be aware when using Kp expressions to check units!