q and delta H


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Harmony Becerra
Posts: 32
Joined: Sun Jan 21, 2018 3:00 am

q and delta H

Postby Harmony Becerra » Sat Mar 16, 2019 10:32 pm

Hello, I was wonder if q and delta H are the same thing? Because I see them being use interchangeably.

Ariel Cheng 2I
Posts: 67
Joined: Fri Sep 28, 2018 12:29 am

Re: q and delta H

Postby Ariel Cheng 2I » Sat Mar 16, 2019 10:37 pm

I think q = delta H under constant pressure. I also think that delta H implies constant pressure already so they can be used interchangeably but I am not sure.

Douglas Nguyen 2J
Posts: 71
Joined: Fri Sep 28, 2018 12:15 am

Re: q and delta H

Postby Douglas Nguyen 2J » Sat Mar 16, 2019 10:42 pm

q is equal to delta H when pressure is constant.

This gives you:

delta U = delta H - P(delta V)

Ronald Thompson 1F
Posts: 59
Joined: Fri Sep 28, 2018 12:25 am

Re: q and delta H

Postby Ronald Thompson 1F » Sat Mar 16, 2019 10:43 pm

They can be used interchangeably

paytonm1H
Posts: 74
Joined: Fri Sep 28, 2018 12:18 am

Re: q and delta H

Postby paytonm1H » Sat Mar 16, 2019 10:43 pm

the definition of enthalpy is the change in heat of a system at constant pressure. so q = deltaH at constant pressure.

Aurbal Popal
Posts: 63
Joined: Fri Sep 28, 2018 12:27 am

Re: q and delta H

Postby Aurbal Popal » Sat Mar 16, 2019 11:24 pm

delta H = delta U + P delta V

when there is a constant pressure,

delta H= q

I think the q comes from the delta U (as delta U= q +w)

Hope this helps.

lukezhang2C
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

Re: q and delta H

Postby lukezhang2C » Sun Mar 17, 2019 3:13 pm

So Delta U = q + w = q - PdeltaV, meaning that under constant pressure U = q = delta H. This is where most of the interchangeability comes from as systems with constant pressure appear often in our problems.


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