Reversible Processes

[Miriam Restrepo 2D]

How is P external kept equal to P for a reversible process?

[martha-1I]

if you're referring to when we want to find work, then you are using the wrong equation for the reversible process. You are thinking of the equation for the irreversible process which is w=-P_exV. For reversible processes, we use w=-nRTln(v₂/v₁) since we are assuming that all heat lost is converted into work.

[Niharika Reddy 1D]

I think Martha may've switched the order of the initial and final volumes around in the equation for the work of a reversible process. It should be V₂/V₁, or V_final/V_initial; w_reversible=-nRTln(V_final/V_initial)

[martha-1I]

oh yes I did. Sorry about that. I will go back and edit it. Thank you!

[Justin Le 2I]

Figure 7.16 on page 249 has a good visualization of the difference between reversible and irreversible processes. Note that the pressure in the reversible graph is not constant whereas the pressure in the irreversible graph is constant.