Isothermal, Delta U = 0

isochoric/isometric: $\Delta V = 0$
isothermal: $\Delta T = 0$
isobaric: $\Delta P = 0$

Kelly Huang 3L
Posts: 18
Joined: Fri Sep 25, 2015 3:00 am

Isothermal, Delta U = 0

For isothermal, Delta U = 0, since delta U = q + w, how do you know if it's -q=w or q=-w?

Joyce Xiong 4C
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Re: Isothermal, Delta U = 0

Hey there!

There is no difference between q=-w and -q=w: they are the same thing, and both are saying that when delta U is 0, the work leaving the system is replaced by the q entering in the system, or vice versa, work done on the system results in the loss of heat. The value of w and q are the same but the sign is not. When you solve a problem, you usually just find the value of one, and if the system is isothermal, the value of the other is its negative.

Gabriel Esmailian 1F
Posts: 12
Joined: Tue Nov 25, 2014 3:00 am

Re: Isothermal, Delta U = 0

Both situations are the same. The signs just refer to whether the system is doing work, losing energy, etc. So depending on the situation, the q or w could be negative.