## enthalpy of phase changes

205389184
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### enthalpy of phase changes

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

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

### Re: enthalpy of phase changes

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

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

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

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

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

### Re: enthalpy of phase changes

I do not believe that enthalpy values will ever be negative

Posts: 104
Joined: Fri Aug 09, 2019 12:16 am

### Re: enthalpy of phase changes

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

DHavo_1E
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### Re: enthalpy of phase changes

Hello,

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

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

### Re: enthalpy of phase changes

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.