### Work equation

Posted:

**Mon Feb 04, 2019 12:15 pm**How do you differentiate which work equation to use?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=129&t=41350

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Posted: **Mon Feb 04, 2019 12:15 pm**

How do you differentiate which work equation to use?

Posted: **Mon Feb 04, 2019 2:44 pm**

One is used when the system is at constant pressure (irreversible expansion) (w=-pdeltaV) and the other is used when pressure is not constant (usually isothermal reversible expansion) (w=-nRT*ln(Vf/Vi)).

Posted: **Mon Feb 04, 2019 3:02 pm**

W=-PdeltaV is utilized when pressure IS constant which was shown in lecture through a definite integral because we could factor out the constant of pressure and we are left with the integral dv which just means V2-V1 if we put it into a definite integral. We use the other equation -nRTln(V2/V1) when pressure IS NOT constant, and the derivation of this formula was shown in class today.