Enthalpy diagram

Question

Frost forms on the windshield of a car on a cold winter morning. This frost disappears with no evidence that water forms.

Draw an enthalpy diagram to illustrate the change.

Answer 1

Hi Luhan E.,

How about you make time the x-axis, y-axis the enthalpy of the water in question (as frost, then as vapor). Don't forget (for quatitative scale) that sublimation=the combined enthalpy gain of melt+boil =80+540 cal/g. By the way, if you wanted to REALLY impress your instructor, then: show the reverse process (deposition), with the reverse "cliff" down, during the late night (radiant cooling of the car windshield to the night sky superchills it), a little decrease as it cools further, then a little increase as it warms up at dawn, and finally a step up as it sublimes. Then a broken line to right, and another cliff down to liquid water (only) (540 cal/g), + "Into every life a little rain must fall...." Label the other transitions, too, with names, and .delta.H's

-- Cheers, --Mr. d.