Negative

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Nathan Mariano 2G
Posts: 68
Joined: Fri Sep 28, 2018 12:29 am

Negative

Postby Nathan Mariano 2G » Fri Feb 08, 2019 7:34 pm

When performing heat transfer problems, why is heat that is lost a positive q value and why is heat that is gained a negative q value?

Kristen Kim 2K
Posts: 70
Joined: Fri Sep 28, 2018 12:16 am

Re: Negative

Postby Kristen Kim 2K » Fri Feb 08, 2019 8:10 pm

The first law of thermodynamics states that energy is neither created nor destroyed, therefore the overall amount of heat (q) needs to be the same.
system + surroundings = universe
In heat transfer, if one substance X is losing heat to another substance Y, then substance Y must be gaining the heat that is lost by substance X.

Xinyi Zeng 4C
Posts: 63
Joined: Fri Sep 28, 2018 12:18 am

Re: Negative

Postby Xinyi Zeng 4C » Fri Feb 08, 2019 8:13 pm

I think it depends on which direction you are looking at?
If the heat is lost from the system to the surroundings, then the system's change in enthalpy should be negative while the change in enthalpy of the surroundings should be positive, vice versa. One thing for sure is that if the reaction releases heat(exothermic), then delta H should be negative; if the reaction absorbs heat (endothermic), then delta H should be positive.

Nathan Mariano 2G
Posts: 68
Joined: Fri Sep 28, 2018 12:29 am

Re: Negative

Postby Nathan Mariano 2G » Fri Feb 08, 2019 10:28 pm

Kristen Kim 2K wrote:The first law of thermodynamics states that energy is neither created nor destroyed, therefore the overall amount of heat (q) needs to be the same.
system + surroundings = universe
In heat transfer, if one substance X is losing heat to another substance Y, then substance Y must be gaining the heat that is lost by substance X.


When performing the heat transfer equation (q(heat loss)=q(heat gained), then, which substance is the negative value?

Rian Montagh 2K
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

Re: Negative

Postby Rian Montagh 2K » Fri Feb 08, 2019 10:58 pm

The heat loss should be negative and the heat gained should be positive.


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