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### Phase Change Question

Posted: **Fri Jan 19, 2018 6:32 pm**

by **Connie2I**

Was there a formula to use when calculating a phase change like vaporization or anything? In the notes it said something like deltaH of vaporization = H vapor - H liquid, but the solutions manual for problem 8.37 seems to use q and moles instead so I wasn't sure

### Re: Phase Change Question

Posted: **Fri Jan 19, 2018 7:51 pm**

by **Lisa Tang 1C**

For 8.37, you consider the units that enthalpy is reported in (kJ/mol). So, you should divide the heat (measured in kJ) by moles of the substance to find delta H of vaporization.

### Re: Phase Change Question

Posted: **Sat Jan 20, 2018 4:33 pm**

by **Charles Ang 1E**

H_{vap} = kJ/moles is what the book gives as the value of enthalpy of vaporization. For the question, we are given a value in kJ and in moles. Just put those value into the formula to get the answer.

### Re: Phase Change Question

Posted: **Sat Jan 20, 2018 4:51 pm**

by **Rakhi Ratanjee 1D**

Generally, when you have to find the energy required for a phase change, use the formula Energy (q) = (mass of sample)*(heat of fusion/vaporization of substance in J/g)