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

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 P_ext 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 P_ext is almost equal to P_ext.

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, .P_ext