By convention, species to the left of the arrows are called reactants, and those on the
right side of the arrows are called products. As Berthollet discovered, writing a reaction
in this fashion does not guarantee that the reaction of A and B to produce C and
D is favorable. Depending on initial conditions, the reaction may move to the left, to
the right, or be in a state of equilibrium. Understanding the factors that determine
the final position of a reaction is one of the goals of chemical thermodynamics.
Chemical systems spontaneously react in a fashion that lowers their overall free
energy. At a constant temperature and pressure, typical of many bench-top chemical
reactions, the free energy of a chemical reaction is given by the Gibb’s free energy
function