Delta H






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Briana Yik 1H
Posts: 30
Joined: Fri Sep 28, 2018 12:20 am

Delta H

Postby Briana Yik 1H » Tue Feb 19, 2019 11:10 pm

why does delta H positive not favor the forward process?

Mona Lee 4L
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Joined: Fri Sep 28, 2018 12:16 am

Re: Delta H

Postby Mona Lee 4L » Tue Feb 19, 2019 11:46 pm

DeltaH alone cannot determine if a reaction is spontaneous or not, which is why you need to use VanHoff's equation. For example, some endothermic reactions will be spontaneous when they occur at very high temperatures.

Irene Zhou 1E
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Joined: Fri Sep 28, 2018 12:18 am

Re: Delta H

Postby Irene Zhou 1E » Wed Feb 20, 2019 12:47 am

Change in enthalpy alone does not determine the spontaneity of the reaction. It also depends on the change in entropy and temperature.

Sarah Kiamanesh 1D
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Joined: Fri Sep 28, 2018 12:22 am

Re: Delta H

Postby Sarah Kiamanesh 1D » Wed Feb 20, 2019 7:16 pm

delta G = delta H - Tdelta S
spontaneity (denoted by either a positive or negative gibbs value) depends on both the change in enthalpy of the reaction as well as the temperature and change in entropy. Enthalpy alone is not enough to determine spontaneity

Kathryn Wilhem 1I
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Joined: Fri Sep 28, 2018 12:27 am

Re: Delta H

Postby Kathryn Wilhem 1I » Wed Feb 20, 2019 10:14 pm

There is a chart in the 7th edition pg. 330 that I found helpful for this. It's table 4J.1.
I can write it here also:
Delta H Delta S Spontaneous?
negative positive yes, delta G < 0
negative positive yes, if TdeltaS < deltaH and deltaG < 0
positive positive yes, if TdeltaS > deltaH and deltaG < 0
positive negative no, deltaG > 0

George Ghaly 2L
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Re: Delta H

Postby George Ghaly 2L » Thu Feb 21, 2019 8:50 pm

A change In enthalpy alone cannot determine the spontaneous nature of a system as the entropy of the system and the temperature the reaction is taking place at are also needed to determine the spontaneity of a reaction.


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