Predicting Reaction Outcomes

Chemical kinetics describes the rate and path by which reactants move from one state to another in the reaction pathway, whereas thermodynamics considers the relative stabilities of the states themselves.

Compounds A and B can react with each other in two possible pathways, one leading to products C and D, and the other leading to products E and F.

Products C and D are kinetically favored over E and F, as their formation requires smaller activation energy. Moreover, they are thermodynamically more favorable on account of their lower energies.

In most cases, a reaction pathway is both thermodynamically and kinetically favored, although there are instances where thermodynamics and kinetics oppose each other.

In this case, products C and D are favored by thermodynamics because they have lower energy. However, products E and F are preferred by kinetics because their formation involves lower energy of activation.

Temperature plays an important role in determining the major product. At low temperatures, products E and F form rapidly, whereas at high temperatures, equilibrium concentrations are quickly achieved, producing C and D.

If the activation energy barrier is sufficiently high, the