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delta U = q + w

Posted: Mon Feb 10, 2020 11:39 pm
by Jasmine W 1K
In this equation: delta U = q + w, how would you know whether or not work would be positive or negative?

Re: delta U = q + w

Posted: Tue Feb 11, 2020 12:09 am
by JesseAuLec1Dis1G
I think all of it is in terms of the system. So if the system is doing work than work is positive.

Re: delta U = q + w

Posted: Tue Feb 11, 2020 12:10 am
by Wendy 1E
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.

Re: delta U = q + w

Posted: Tue Feb 11, 2020 12:38 am
by Elizabeth Bowen 1J
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.

Re: delta U = q + w

Posted: Tue Feb 11, 2020 1:22 am
by alex_4l
W is positive when work is done BY the system
W is negative when work is done ON the system

Re: delta U = q + w

Posted: Tue Feb 11, 2020 1:23 am
by alex_4l
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

Re: delta U = q + w

Posted: Tue Feb 11, 2020 3:01 pm
by Michelle Xie 2B
it depends on the system.