 # What are the expressions for work done in different process and how to identify a process by the graphs.

11 years ago

Dear student,

ii) Work done in irreversible isothermal expansion : Two types of irreversible isothermal expansions are observed, i.e., (a) Free expansion and (b) Intermediate expansion. In free expansion, the external pressure is zero, i.e., work done is zero when gas expands in vacuum. In intermediate expansion, the external pressure is less than gas pressure. So, the work done when volume changes from V1 to V2 is given by Since Pext is less than the pressure of the gas, the work done during intermediate expansion is numerically less than the work done during reversible isothermal expansion in which Pext is almost equal to Pext.

Irreversible adiabatic expansion : In free expansion, the external pressure is zero, i.e, work done is zero. Accordingly, E which is equal to w is also zero. If E is zero, T should be zero. Thus, in free expansion (adiabatically), T = 0, E = 0, w = 0 and H = 0.

In intermediate expansion, the volume changes from V1 to V2 against external pressure, .Pext 