sentence: equation arrhenius ' equation gives the dependence of the rate constant of a chemical reaction on the absolute temperature ( in kelvin ) , where is the pre-exponential factor ( or simply the prefactor ) , is the activation energy , and is the universal gas constant : alternatively , the equation may be expressed as the only difference is the energy units of : the former form uses energy per mole , which is common in chemistry , while the latter form uses energy per molecule directly , which is common in physics .