Phase Change Question

[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

[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.

[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.

[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)