ABSTRACT
The free energy for the reaction also sets the value of K, the ratio of the activities for the products over the reactants and the extent of reaction. All chemical reactions have both a forward rate of reaction and a reverse rate, so that a dynamic equilibrium state, of constant composition, is achieved when the forward rate equals the reverse rate of reaction. The extent of reaction needed to achieve that balance then defines K, the equilibrium constant, either in pressures (if a gaseous reaction) or mole fractions or molarities, if in the solution phase. Since K can only change value if T changes, pressure changes cannot change the value of Kp. However, if the equilibrium system involves gases, the equilibrium composition can be altered when the total pressure changes to keep the partial pressure ratio defined by K. Using Faraday’s constant, F, the ∆G for any redox reaction can be expressed as a voltage, potential difference (∆E) or emf.
