Heat Released/Absorbed  [ENDORSED]

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Carla Cruz Medina 1L
Posts: 12
Joined: Fri Sep 25, 2015 3:00 am

Heat Released/Absorbed

Postby Carla Cruz Medina 1L » Sun Jan 22, 2017 7:56 pm

Is heat absorbed always negative and heat released always positive? Why is that so?

Maggie Bui 1H
Posts: 35
Joined: Fri Jul 22, 2016 3:00 am
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Re: Heat Released/Absorbed  [ENDORSED]

Postby Maggie Bui 1H » Sun Jan 22, 2017 8:03 pm

Hm, I think you have them mixed up? Heat released is negative and heat absorbed is positive.

This all goes back to the concept of a system and the surroundings. The system is what we're focusing on while the surroundings are everything else. We think of change in energy from the perspective of the system. Therefore, when we say the system releases heat, we think of that as energy leaving the system, hence the negative sign. Conversely, when the system absorbs heat, energy is entering the system, hence the positive sign.

Rika Jitosho 2E
Posts: 29
Joined: Fri Jun 17, 2016 11:28 am

Re: Heat Released/Absorbed

Postby Rika Jitosho 2E » Sun Jan 22, 2017 8:08 pm

Hi Carla,

It was helpful for me to remember that qp = H = enthalpy. qp gives a measure of heat released or absorbed at a constant pressure.

Enthaply, or H will be negative if the system is losing heat; therefore the system is cold, and the surroundings, hot. This type of reaction would be an exothermic reaction.
Enthalpy, or H will be positive if the system is gaining heat. This makes the system hot, and the surroundings cold. This type of reaction would be an endothermic reaction.

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