DeltaHsub

[Delaney Smith 1C]

Can someone explain why DeltaHsub = DeltaHfus + DeltaHvap?

[Jonathan Gong 2H]

DeltaHfus is the enthalpy change when a substance changes phase from solid to liquid (melts). DeltaHvap is the enthalpy change when a substance changes phase from liquid to vapor (vaporizes). And, deltaHsub is the enthalpy change when a substance changes phase from solid to vapor (sublimates). DeltaHsub = DeltaHfus + DeltaHvap works because the enthalpy change when a substance sublimates will be the sum of the enthalpy change if it first melts and then vaporizes.

[Kaylee Sepulveda 4G]

The reason that the ΔH_sublimation is equal to the ΔH_fusion + ΔH_vaporization is that sublimation is the transition from the solid phase to the gas phase without passing through an intermediate liquid phase. So, from this, we can infer that adding the ΔH of the transition from solid to liquid and the ΔH of the transition from liquid to gas would equal the net ΔH of the transformation from solid to gas.