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enthalpy of phase changes

Posted: Sun Jan 26, 2020 8:29 pm
by 205389184
Will a calculation of the enthalpy of vaporization, fusion, or sublimation ever result in a negative value?

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 8:49 pm
by Aliya Jain 2B
I dont think so, because heat is always required during those phase changes

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 8:58 pm
by KSong_1J
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)

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 9:02 pm
by 405268063
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.

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 9:04 pm
by RasikaObla_4I
No because it requires heat energy to go from a solid to a liquid to vapor so the reactions would be endothermic.

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 9:11 pm
by 605395381
I do not believe that enthalpy values will ever be negative

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 9:16 pm
by Eesha Chattopadhyay 2K
No, calculating the enthalpy of a phase change will not be negative.

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 9:26 pm
by DHavo_1E
Hello,

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

Re: enthalpy of phase changes

Posted: Sun Jan 26, 2020 9:51 pm
by AGaeta_2C
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.