## the sign of q and w [ENDORSED]

cristiancampana 2H
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Joined: Fri Sep 29, 2017 7:07 am

### the sign of q and w

why is it that sometimes q and w are negative, but in the equation ΔU= q+w they are both positive such in 8.11

Chem_Mod
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### Re: the sign of q and w  [ENDORSED]

The expression q + w can allow for q or w or both to have positive or negative numbers. For example, if q = -2.3 J and w = 5.0 J then the expression becomes q + w = -2.3 J + 5.0 J.

Fatima_Iqbal_2E
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### Re: the sign of q and w

Because that is the general formula, both q + w would be positive, as you'd be adding their contributions together. If there was a -q or a -w, you would then add it into the equation as a negative number.

Ashley Macabasco 2K
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### Re: the sign of q and w

In the equation ΔU= q+w both q and w are positive to show that the change in internal energy consists of both the transfer of heat and the transfer of work in a closed system. Because the heat transfer may be negative (due to the system losing heat) or positive (due to the system gaining heat), q can be either negative or positive and the same goes for work as work can be done by a system or done on the system.

Yu Chong 2H
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Joined: Fri Sep 29, 2017 7:05 am

### Re: the sign of q and w

ΔU= q+w does not necessarily mean that q and w are positive, they can take on negative values as well. The sum of the two, regardless of them being positive or negative will be the change in internal energy of the system.

Michael Cheng 1C
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### Re: the sign of q and w

so if w decreases, will the internal energy of the system increase or decrease?

Silvino Jimenez 1A
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Joined: Fri Sep 29, 2017 7:04 am

### Re: the sign of q and w

"If w decreases, will the internal energy increases or decreases"

It depends if w is positive or negative
- if the work done on the system decreases (+w)
The change in internal energy of the system (deltaU) decreases

Or

- if the work done by the system decreases (-w)
deltaU increases