Reversible expansion and work in a vacuum


and

Moderators: Chem_Mod, Chem_Admin

ZoeHahn1J
Posts: 63
Joined: Sat Jul 22, 2017 3:01 am
Been upvoted: 1 time

Reversible expansion and work in a vacuum

Postby ZoeHahn1J » Wed Jan 24, 2018 5:08 pm

In lecture today, Dr. Lavelle described that a gas expanding against a vacuum is reversible, and that as it expands, it does work against the piston (loses energy) that is then compensated by the heat (gain in energy). I'm a little confused, however, how could the gas be said to be doing work when it's expanding against a vacuum? Thank you so much!

Deap Bhandal L1 S1J
Posts: 77
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 2 times

Re: Reversible expansion and work in a vacuum

Postby Deap Bhandal L1 S1J » Wed Jan 24, 2018 7:40 pm

I believe the piston had a string with mass attached to it on the outside of the chamber. Not fully sure, but I would recommend looking at the picture in your notes again.

Amanda Wu 2C
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am

Re: Reversible expansion and work in a vacuum

Postby Amanda Wu 2C » Wed Jan 24, 2018 7:50 pm

As I recall from the book, a system does no expansion work when it expands into a vacuum because there is not an opposing force (pressure is 0). However, in Lavelle's lecture today, I believe he included a mass that was outside the vacuum chamber attached to the piston by a string. Because the expansion of the gas, though in a vacuum, raises the mass and work, as explained in the book is "the transfer of energy to a system by a process that is equivalent to raising or lowering a weight," work is being done.


Return to “Calculating Work of Expansion”

Who is online

Users browsing this forum: No registered users and 2 guests