delta U = q + w

Jasmine W 1K
Posts: 49
Joined: Sat Sep 07, 2019 12:18 am

delta U = q + w

In this equation: delta U = q + w, how would you know whether or not work would be positive or negative?

JesseAuLec1Dis1G
Posts: 52
Joined: Mon Jun 17, 2019 7:23 am

Re: delta U = q + w

I think all of it is in terms of the system. So if the system is doing work than work is positive.

Wendy 1E
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Re: delta U = q + w

If work is done on the system by the surroundings, then work is positive. If work is done by the system onto the surroundings, then work is negative. This is because when work is done by the system, the system loses energy.

Elizabeth Bowen 1J
Posts: 53
Joined: Wed Nov 14, 2018 12:20 am

Re: delta U = q + w

you can think about it the same way as when enthalpy is positive or negative—> it’s negative if the system is giving off heat, just like if the system is doing work (or “giving off” work so to speak), and like with enthalpy, it’s positive when the system is gaining heat, or when heat is being given to/absorbed by the system, just like when work is being done on the system.

alex_4l
Posts: 109
Joined: Thu Sep 26, 2019 12:18 am

Re: delta U = q + w

W is positive when work is done BY the system
W is negative when work is done ON the system

alex_4l
Posts: 109
Joined: Thu Sep 26, 2019 12:18 am

Re: delta U = q + w

alex_4l wrote:W is positive when work is done BY the system
W is negative when work is done ON the system

That being said, this is only for the equation of delta U = Q + W implying that it is a closed system with no other factors involved

Michelle Xie 2B
Posts: 99
Joined: Sat Aug 17, 2019 12:18 am

Re: delta U = q + w

it depends on the system.

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