enthalpy of phase changes

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205389184
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Joined: Sat Sep 07, 2019 12:18 am

enthalpy of phase changes

Postby 205389184 » Sun Jan 26, 2020 8:29 pm

Will a calculation of the enthalpy of vaporization, fusion, or sublimation ever result in a negative value?

Aliya Jain 2B
Posts: 101
Joined: Wed Sep 11, 2019 12:16 am

Re: enthalpy of phase changes

Postby Aliya Jain 2B » Sun Jan 26, 2020 8:49 pm

I dont think so, because heat is always required during those phase changes

KSong_1J
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Joined: Thu Jul 11, 2019 12:17 am

Re: enthalpy of phase changes

Postby KSong_1J » Sun Jan 26, 2020 8:58 pm

The textbook states that enthalpies of fusion and vaporization are always positive and I’m pretty sure the same goes for the enthalpy of sublimation (since it’s the conversion of a solid to vapor so it’s endothermic)

405268063
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Joined: Thu Jul 25, 2019 12:17 am

Re: enthalpy of phase changes

Postby 405268063 » Sun Jan 26, 2020 9:02 pm

I would think that since heat is required to make those phase changes, the reaction would be endothermic. Therefore, delta H would have to be positive.

RasikaObla_4I
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Joined: Thu Jul 25, 2019 12:15 am

Re: enthalpy of phase changes

Postby RasikaObla_4I » Sun Jan 26, 2020 9:04 pm

No because it requires heat energy to go from a solid to a liquid to vapor so the reactions would be endothermic.

605395381
Posts: 50
Joined: Mon Jun 17, 2019 7:24 am

Re: enthalpy of phase changes

Postby 605395381 » Sun Jan 26, 2020 9:11 pm

I do not believe that enthalpy values will ever be negative

Eesha Chattopadhyay 2K
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Joined: Fri Aug 09, 2019 12:16 am

Re: enthalpy of phase changes

Postby Eesha Chattopadhyay 2K » Sun Jan 26, 2020 9:16 pm

No, calculating the enthalpy of a phase change will not be negative.

DHavo_1E
Posts: 118
Joined: Sat Aug 17, 2019 12:17 am

Re: enthalpy of phase changes

Postby DHavo_1E » Sun Jan 26, 2020 9:26 pm

Hello,

In response to this question, could anyone explain why the bond enthalpies in Dr. Lavelle's example were positive AND negative?

AGaeta_2C
Posts: 112
Joined: Wed Sep 18, 2019 12:21 am

Re: enthalpy of phase changes

Postby AGaeta_2C » Sun Jan 26, 2020 9:51 pm

DHavo_1E wrote:Hello,

In response to this question, could anyone explain why the bond enthalpies in Dr. Lavelle's example were positive AND negative?


Bond energy can be described as the energy it takes to break a bond, in this case, the values would be positive.
Therefore, the energy it takes to form bonds would be negative.


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