ABSTRACT
Reaction velocities and rate constants depend on temperature. As a rule of thumb, reaction velocities increase by a factor of 2–4 for each increase in temperature by 10° C. Reactants and products of a reaction have a free energy G, which is the sum of their standard free energies of formation. Reactants A and B and products P are separated from each other by an energy barrier, the activation barrier. An alternative approach to reaction velocities assumes that the reaction velocity is proportional to the number of collisions Z of the reactants, and to the probability that they collide with sufficient energy for the reaction to occur. The reaction velocity depends on the height of the energy barrier that separates the reactant(s) from the product(s). Therefore, a thermodynamically favorable reaction might occur very slowly if the activation energy is high.
