## Heat and Work relation

Chew 2H
Posts: 34
Joined: Fri Sep 29, 2017 7:05 am

### Heat and Work relation

Based on the deltaU=q+w equation, if a system is endothermic and q is positive, would the work always be negative? If not, when does it become positive?

Jakob von Morgenland 2C
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Joined: Sat Jul 22, 2017 3:00 am
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### Re: Heat and Work relation

I don't think the work needs to be negative if the given q is positive; I believe it is not a causal relationship ("if q is positive, then w must be negative", etc.). If you take a look at 8.13, you can see that this problem gives a negative deltaU value and a negative (but not as large) deltaH value, so therefore a large negative w value is needed.

Sarah 2F
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

### Re: Heat and Work relation

In that equation q and w are separate so they don't directly affect each other since they are calculated separately.

Sophie 1I
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am

### Re: Heat and Work relation

Not necessarily for this equation.

Jimmy Zhang Dis 1K
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: Heat and Work relation

Normally when solving delta U = q(heat) + w(work) q and w are calculated separately. The work could have a negative or positive value depending on the delta V in the equation.

Guangyu Li 2J
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Joined: Fri Sep 29, 2017 7:07 am
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### Re: Heat and Work relation

The value of work is not necessarily negative.

According to what the textbook states in CH8: First Law of thermodynamics, △U=q+w
1. the q and w is determined by the realistic circumstance
2. the positive and negative sign is assigned to represent that if the work is done to the system and the system does work to the surroundings (or if the heat is transferred from the system to the surroundings or from the surroundings to the system)
3. the values of q and w are actually really random

Hope this helps!

Warda Sahib 2J
Posts: 29
Joined: Thu Jul 13, 2017 3:00 am

### Re: Heat and Work relation

No, the work doesn't necessarily have to be negative in this case.