Work Done On or By System

Moderators: Chem_Mod, Chem_Admin

Amanda Mac 1C
Posts: 58
Joined: Fri Sep 29, 2017 7:05 am

Work Done On or By System

Postby Amanda Mac 1C » Tue Jan 23, 2018 12:03 am

How do you differentiate between whether work is done ON a system or BY the system?

Yashaswi Dis 1K
Posts: 56
Joined: Fri Sep 29, 2017 7:04 am

Re: Work Done On or By System

Postby Yashaswi Dis 1K » Tue Jan 23, 2018 2:01 am

Work done by system: negative sign for work

Work done on system: positive sign for work.

Another way to help differentiate the two:
Think of the equation: w= -P * (delta V).
---->If volume expansion occurs, then final volume minus initial volume is going to be positive so with the negative sign in the front of the equation, work will be negative and so the system DID work on the surroundings.

---->If volume compression occurs, final - initial volume (delta V) will be negative, so when you have the negative times the negative sign in the front of the equation, you get a positive value for work, so work was done ON the system.

A friend told me her analogy to help her remember: doing work by herself (the system of interest) requires work and so that can be negative for her whereas when someone else (the surroundings) does something for her, she feels good.

Hope that helps! Good luck for your test!


Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

Who is online

Users browsing this forum: No registered users and 1 guest