## Phase Change and Enthalpy

$\Delta U=q+w$

Janice Ly 2F
Posts: 9
Joined: Fri Sep 25, 2015 3:00 am

### Phase Change and Enthalpy

When doing problems that include a chemical going from hot to cold, does it necessarily mean that it goes through a phase change and you have to add (moles x enthalpy of the possible phase change) to the amount of heat? I remember the problem about dry ice on the midterm and didn't know whether to add a phase change.

Kim Vu 2G
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

### Re: Phase Change and Enthalpy

For the midterm, I did not add a phase change because the substance was not water and so you wouldn't be able to know the enthalpy of fusion since it was not given. It depends on how much temperature the change is say water going from -10 to 110 degrees Celsius, there are going to be phase changes from solid, liquid and gas and change in enthaply of fusion and evaporation but since the substance's boiling pt/freezing pt was not given either, I assumed that we didn't need to calculate the heat of fusion.