A reversible chemical reaction results in an equilibrium mixture of reactants and products. In this reaction it involves two reactants and two products. Chemical equilibrium in a chemical process is the state in which the chemical activities or concentrations of the reactants and their products have no net change over the course of the process. This is generally the state where the forward chemical process proceeds at the same rate as the reverse reaction process. These opposite actions are usually not zero, but rather they are equal. There is no change to any of the reactants or concentrations.

In a chemical reaction, when two or more reactants are combined and mixed together then heated if necessary, the whole of the reactants do not get converted into the products. The time it takes for these reactants to act may be a fast as a millionth of a second, or it may take as long or longer then the combined age of the universe. The opposite reactions will have equal reaction rates which goes on the create a dynamic equilibrium within the ratio between the reactants and products. This is known as chemical equilibrium. This concept was developed by Bertollet in 1803, and it also realized that some chemical reactions are reversible.

In order for any chemical reaction to considered as equilibrium, the rate of the forward and the reverse reactions have to be equal. The equilibrium position of a reaction is known to lie far to the right. If at the point of equilibrium, almost all the reactants are used up and far to the left, even if very little product is created from the reactants.

The relationship between the equilibrium constant and Gibbs energy can be seen by contemplating the chemical potentials. When it is at a constant temperature and pressure, the function ‘G’ (Gibbs free energy) used for the reaction depends only with the extent of the reaction. This temperature can only decrease according to the second law of thermodynamics. Gibbs energy is stated in thermodynamics that is the thermal potential which measure the relevant, useful or process initiating work that is able to be obtained from an isothermal, isobaric thermodynamic system. Gibbs free energy is the absolute most amount to non-expansion work that can be extracted from a closed system. It can only be produced in a completely reversible reaction.

The second law of thermodynamics is a saying describing the universal principle of increasing entropy. Entropy is an information theoretical concept applied across physics, information theory, mathematics and other branches of science and engineering. The entropy of an isolated system which is not in equilibrium will most likely increase over the course of time. The entropy change of the system, where any infinitesimal reversible process is given by δq / T, where by δq is the heat supplied to the system and T is the absolute temperature of the system. In certain thermodynamics, the second law is a result of applying the same previous probability past postulate. This is different then in statistical thermodynamics, the second law is the result of the application of the equal prior chance postulate to any future one.