## Phase Change

Wilson 2E
Posts: 100
Joined: Sat Aug 17, 2019 12:18 am

### Phase Change

How do you determine the value of the change in enthalpy between phase states?

KDang_1D
Posts: 127
Joined: Fri Aug 30, 2019 12:15 am
Been upvoted: 1 time

### Re: Phase Change

The information should be given, possibly in a phase change graph. I believe it would be the difference in y-value between two of the horizontal lines (the height of the diagonal) as this would be the energy into the system to bring the substance from one state up to the next.

Posts: 53
Joined: Fri Aug 02, 2019 12:16 am

### Re: Phase Change

KDang_1D wrote:The information should be given, possibly in a phase change graph. I believe it would be the difference in y-value between two of the horizontal lines (the height of the diagonal) as this would be the energy into the system to bring the substance from one state up to the next.

Yes, it should be given, either as a phase change graph or as stated values. Stated values will look like delta H (fus) = some number, and that means that the number they give is the phase change enthalpy from solid <--> liquid. delta H (vap) refers to liquid <--> gas.
Also, I think the phase change enthalpy on a graph is actually the horizontal line; the diagonal line happens when temperature is rising and the horizontal line happens when heat is being used not to raise temperature, but to change phases

Jessica Li 4F
Posts: 115
Joined: Fri Aug 09, 2019 12:16 am

### Re: Phase Change

Those values should be given to you (I.e. the heat of vaporization of water is 40.7 kJ/mol), but it is up to you to multiply those values accordingly depending on how much of something you have (I.e. moles of water).

Juliet Stephenson 4E
Posts: 100
Joined: Wed Sep 18, 2019 12:21 am

### Re: Phase Change

I also think it would be possible that we would have to calculate the phase change enthalpy for sublimation based on given values of vaporization and fusion.