Delta H and Delta U

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Mary Becerra 2D
Posts: 53
Joined: Fri Sep 29, 2017 7:06 am

Delta H and Delta U

Postby Mary Becerra 2D » Sat Jan 13, 2018 8:21 pm

Why can we equate delta H (heat transfer at constant pressure) and delta U (heat transfer at constant volume)?

Sarah_Stay_1D
Posts: 57
Joined: Sat Jul 22, 2017 3:00 am
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Re: Delta H and Delta U

Postby Sarah_Stay_1D » Sat Jan 13, 2018 9:04 pm

Mary Becerra 2D wrote:Why can we equate delta H (heat transfer at constant pressure) and delta U (heat transfer at constant volume)?

You can not always equate delta H (enthalpy) to delta U (internal energy). The two are only equal when you have constant pressure and constant volume. This is true because at constant pressure ΔH = ΔU + PΔV. So, if the volume is constant, the change in volume would be 0. Therefore, ΔH = ΔU + P(0) so, ΔH =ΔU.

204918982
Posts: 50
Joined: Fri Sep 29, 2017 7:04 am

Re: Delta H and Delta U

Postby 204918982 » Sun Jan 14, 2018 1:59 pm

Yes this is only true when the pressure and volume are constant

Wayland Leung
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Re: Delta H and Delta U

Postby Wayland Leung » Sun Jan 14, 2018 4:03 pm

How are the equations for delta h and delta u different? Are there differenet variables in each equation?


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