The number of molecules in one mole of any pure substance is known as Avogadro's number (`N_A`) The total number of molecules, `N`, will be `N = nN_A` where `n` is the number of moles. So the ideal gas law can be written in terms of the number of molecules present: let `k=R/N_A` where `k` is called Boltzmann's constant and have the value `k = (8.314\ J//mol•K)/(6.02 times 10^23\ //mol) = 1.38 times 10^(-23)\ J//K`