heat of formation of water vapor is....

[Smooth Operater]

heat of formation of water vapor is:

B. negative but less negative than the heat of formation of liquid water
C. positive, and more positive than the heat of formation of liqud water.

Which one is correct? And why? Thanks!

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[erichen]

if heat of formation is referring to latent heat, considering that H20 is in its solid phase (ice), then the answer should be positive, and more positive than heat of formation of liquid water, because from the solid phase, it goes through heat of formation of liquid water AND heat of formation of water vapor, since to get from solid to gas, it needs through become liquid first. this is unless the solid sublimates...and i don't think water does that .

the heat of formation can only be negative if it is going from a more active state to a more passive state, i.e. gas->liquid->solid, in which heat is taken out; resulting in the negative value of heat of formation.

hope this helps