The behaviour of many real gases deviates from pV_m=RT . However , at a particular range of temperature and pressure , their behaviour can be represented by the van der Waal's equation :

$\displaystyle (p+\frac{a}{(V_m)^2})(V_m-b)=RT$

in which the values of a and b are characteristics of that particular gas . Determine the units for a and b

Units for $\displaystyle p:Pa , V_m:m^3mol^{-1} , R:Jmol^{-1}K^{-1} , T:K$

THanks ,