Reversible process and greatest work

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Jessa Maheras 4F
Posts: 121
Joined: Fri Aug 02, 2019 12:16 am

Reversible process and greatest work

From Textbook:

If the external pressure were to be increased even infinitesimally at any stage of the expansion, the piston would move in instead of out. Therefore, the work done during a reversible expansion of a gas is the maximum expansion work possible. This is a very important general point:
The greatest work is done for a process that takes place reversibly.

Why is the greatest work done for a process if it takes place reversibly? Greatest compared to what? Is someone able to explain this concept in different words?

Rida Ismail 2E
Posts: 139
Joined: Sat Sep 07, 2019 12:16 am

Re: Reversible process and greatest work

It is comparing reversible to irreversible.

Reversible is able to act as work several times as small perturbations can cause work to be done. With irreversible reactions the work is a tied upon once. Also if you look at the equations, the equation to calculate the w for reversible has more variables effected it and therefore more numbers that are included in the calculation.

Shrayes Raman
Posts: 129
Joined: Sat Jul 20, 2019 12:15 am

Re: Reversible process and greatest work

If you look at the graphs in the textbook it is clear that the reversible formula gives much more area and there for a greater value for integral than the irreversible formula which just is a rectangle. It has to do with the math of the curve vs straight line

Posts: 100
Joined: Wed Sep 18, 2019 12:19 am

Re: Reversible process and greatest work

In a reversible reaction, the countless amount of small movements lead to more work being done when compared to an irreversible reaction where one big action is done causing there to be less overall work

805307623
Posts: 99
Joined: Fri Aug 09, 2019 12:17 am

Re: Reversible process and greatest work

More work can be obtained by increasing the number of stages of a process(allowing the gas to expand against multiple successively lower external pressures). To get the maximum possible work from the process, the expansion should be carried out in an infinite sequence of infinitessimal steps.

Ryan Yoon 1L
Posts: 55
Joined: Mon Jul 01, 2019 12:15 am

Re: Reversible process and greatest work

Since reversible processes use infinitesimally small changes, which leads to more work done.