The energy required to convert one mole of a liquid into vapour at its boiling point is called the
Correct answer: B. molar heat of vaporisation
- A. molar heat of fusion
- B. molar heat of vaporisation
- C. lattice energy
- D. activation energy
Explanation
Molar heat of vaporisation measures the energy needed to overcome the intermolecular forces completely, so it is large for hydrogen bonded liquids such as water at about 40.7 kJ per mole. Heat of fusion is the smaller quantity needed to melt a solid, because melting loosens the lattice without separating the particles. Neither is related to lattice energy, which concerns ionic solids.
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About Evaporation, Boiling Point and Vapour Pressure
Evaporation is the escape of higher-energy molecules from a liquid surface, while vapour pressure is the pressure exerted by vapour in equilibrium with that liquid. The topic distinguishes evaporation from boiling and relates both to temperature, intermolecular forces, surface area, atmospheric pressure and the boiling point.
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