Properties of Chemical Systems and Equilibrium

Values of equilibrium constants K_c and K_p provide valuable information about properties of chemical systems. However, some major factors must be noted while determining equilibrium constants.

• Equilibrium can be achieved only in a closed system, which means no substance can enter or leave the system. If some substances are entering or exiting the system, an equilibrium cannot be reached.
• The equilibrium constant K_c is equal to the reaction quotient Q at equilibrium. When Q is equal to K_c, no further changes in concentrations will happen.
• When the reaction quotient is less than the equilibrium constant $(Q\lt K_{\rm{c}})$, the system is not at equilibrium, and the forward reaction is happening at a greater rate, producing more products.
• When the reaction quotient is greater than the equilibrium constant $(Q>K_{\rm{c}})$, the system is not at equilibrium, and the reverse reaction is happening at a greater rate, producing more reactants.

Comparing the equilibrium constant K_p with the value of partial pressure term provides information about reactions when all of the reactants and products are gases. For a reaction at equilibrium

• The equilibrium constant K_p equals the partial pressure term only at equilibrium. At equilibrium, there will be no change in partial pressures of reactants or products.
• When the partial pressure term is less than K_p, the system is not at equilibrium, and the forward reaction is happening at a greater rate, producing more products.
• When the partial pressure term is greater than K_p, the system is not at equilibrium, and the reverse reaction is happening at a greater rate, producing more reactants.

The ideal gas law can be used to derive a relation between K_c and K_p. The ideal gas law is If all the reactants and the products are gases, the relation between them is given by the equation Here, the term $\Delta n_g$ is the difference between moles of products and moles of reactants.