[vfindia]

The boiling point of anhydrous Hydrofluoric acid is around 20 Celsius.
Data shows that heat of vaporization of anhydrous HF is 7.493 kJ/mol.
How is this possible? Suppose the room temperature is 25 Celsius. Then it will automatically be converted into vapors giving out heat. Then how come heat of vaporization value is positive? Please explain.
Thank you.

[Perito]

The boiling point of anhydrous Hydrofluoric acid is around 20 Celsius.
Data shows that heat of vaporization of anhydrous HF is 7.493 kJ/mol.
How is this possible? Suppose the room temperature is 25 Celsius. Then it will automatically be converted into vapors giving out heat. Then how come heat of vaporization value is positive? Please explain.
Thank you.

The boiling point indicates the temperature at which the material will absorb heat from the surroundings and evaporate. It says nothing about the rate of evaporation. If you put anhydrous HF in a vessel at 20 C and insulated the vessel so that no heat could enter, the material would not evaporate.

A positive heat of vaporization means (by convention) that heat is absorbed when going from a liquid to a gas.

I believe there are materials with negative heats of vaporization, but I can't think of any off hand.