the sign of q and w  [ENDORSED]


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cristiancampana 2H
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the sign of q and w

Postby cristiancampana 2H » Wed Jan 17, 2018 11:45 pm

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]

Postby Chem_Mod » Thu Jan 18, 2018 8:41 am

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

Postby Fatima_Iqbal_2E » Thu Jan 18, 2018 10:22 am

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

Postby Ashley Macabasco 2K » Thu Jan 18, 2018 12:03 pm

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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Re: the sign of q and w

Postby Yu Chong 2H » Fri Jan 19, 2018 2:18 pm

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

Postby Michael Cheng 1C » Fri Jan 19, 2018 5:59 pm

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

Silvino Jimenez 1A
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Re: the sign of q and w

Postby Silvino Jimenez 1A » Sat Jan 20, 2018 11:41 am

To answer the latest question:

"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


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