1) Fleeing away from the system. It will enlarge VG. Imagining there is a boundary, according to Eq. 4, a considerable amount of system work will be done for liquefaction, thereby transferring the kinetic energy to the outer. An example is the Joule-Thomason expansion , in which the gas cools upon expansion. Therefore, if the space of a system is infinitive, it is deduced that those molecules will cool down to 0 K.