In pure component adsorption, two phases coexist at equilibrium in the system: the (ideal) gas phase and the adsorbed phase. In the same way, the Clausius-Clapeyron relation is used to relate temperature and pressure along phase boundaries in a phase diagram, it can also relate temperature and pressure for pure component adsorption systems. For adsorption, the Clausius-Clapeyron relation states that for two different isotherms, T ref and T new , the same loading is obtained at two different pressures P ref i and P new i respectively: