Thermodynamic Background

The law of mass action states that "the rate of a chemical reaction is directly proportional to the product of the molar concentrations of the reactants." It means that the more 'active mass' or 'concentration' of the reactants present, the faster the reaction will proceed.

In a chemical reaction, there are forward and reverse reactions. The forward reaction is the process where the reactants combine to form products. The reverse reaction is the process where the products break down to form the reactants. At equilibrium, the rates of these two reactions are equal, meaning there is no net change in the concentrations of reactants and products.

When we plot the Gibbs energy against the extent of the reaction, the reaction Gibbs energy, ΔG_r, can be interpreted as the slope of the graph. This graphical representation can help visualize how the system's energy changes as the reaction progresses.

If the value of ΔG_r for a particular mixture composition is less than zero, it suggests that the forward reaction will occur spontaneously. If it is more than zero, it implies that the reverse reaction will occur spontaneously.

At constant temperature and pressure, if ΔG_r equals zero for a given composition of the reaction mixture, this indicates an equilibrium state. In other words, the forward and reverse reactions occur at the same rate, and the concentrations of the reactants and products are not changing over time. These fundamental concepts play a crucial role in understanding how chemical reactions occur.