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Reversible Processes

Posted: Wed Feb 06, 2019 9:33 pm
by Lia Inadomi 1I
Can someone explain how you know when it is reversible vs irreversible?

Re: Reversible Processes

Posted: Wed Feb 06, 2019 9:55 pm
by Sam Joslyn 1G
I've talked to a lot of TAs about this, and in general they say that questions on tests will specify whether it is reversible or irreversible. One rule of thumb that may not work all the time but has worked for me is that for ideal gas expansion problems, expansion is reversible if there is a non-constant pressure (w=-nRTln(V2/V1)) and irreversible if the pressure is constant (w=-P*∆V)

Re: Reversible Processes

Posted: Wed Feb 06, 2019 10:19 pm
by Clarissa Cabil 1I
A reversible process is one that can be reversed by an infinitely small change in a variable.
An irreversible process is an expansion against an external pressure that differs by a finite (measurable) amount from the pressure of the system.

In one of the workshops, one of the UAs mentioned how irreversible expansions have constant pressure, and reversible expansions do work against tiny changes and do not have a constant pressure.

Re: Reversible Processes

Posted: Wed Feb 06, 2019 10:20 pm
by marisaimbroane1J
Also, in most real-life examples (like ones that have to do with biochem), the process will be irreversible like Dr. Lavelle mentioned today in lecture. Test questions should specify between the two, though, but you would need to know which work equation to used based on if either the pressure or the volume is constant.

Re: Reversible Processes

Posted: Wed Feb 06, 2019 11:47 pm
by Bianca Barcelo 4I
How does having a non-constant/constant pressure affect the way in which a gas reversibly or irreversibly expands? I am just confused conceptually with how pressure affects the gas.