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Delta H Fusion / Delta H Vaporization

Posted: Sun Jan 21, 2018 2:13 am
by Kathleen Vidanes 1E
In my discussion, we did examples of phase change calculations where the number of moles of the substance and change in enthalpy (fusion and vaporization) were given. To calculate how much energy is needed for the phase change to happen, we used the equation: q=n x deltaH (fusion / vaporization). Does this mean that delta H is equivalent to specific heat x change in temperature, because q also equals n x C x delta T? How?

Thank you!

Re: Delta H Fusion / Delta H Vaporization

Posted: Sun Jan 21, 2018 10:29 am
by Chem_Mod
Hi Kathleen,

The ΔH of fusion and heat found from q=mcΔ,T are both heat applied and measured in units of J or kJ. You only use the q=mCΔT when there is a change in temperature and no change in phase (ex: heating up ice but not forming liquid water yet.) The ΔH of fusion is used when there is no change in temperature. All the heat is instead used to change phase (ex: go from ice to liquid water).

Re: Delta H Fusion / Delta H Vaporization

Posted: Sun Jan 21, 2018 6:40 pm
by vicenteruelos3
the q = n C deltaT is for molar heat capacity