Asked in MDCAT Free Mock 2024 2024

The amount of heat required to form vapors of one mole of a liquid at its boiling point is called?

Correct answer: B. Molar heat of vapourization

  • A. Molar heat of fusion
  • B. Molar heat of vapourization
  • C. Molar heat of sublimation
  • D. Molar heat of Evaporation

Explanation

Option A is incorrect since the molar heat of fusion is the amount of heat required to convert one mole of a substance from the solid to the liquid state at its melting point. Option B is correct since the change from liquid to vapors at its boiling point is called evaporation or vaporization. Since the change is for one mole, we call it the molar heat of evaporation/vaporization. Option C is incorrect since molar heat of sublimation is the amount of heat required to convert one mole of a substance from the liquid to the gaseous state at its sublimation point. Option D is incorrect since molar heat of evaporation is the amount of heat required to convert one mole of a substance from the liquid to the gaseous state at the surface of a boiling liquid. Sublimation is the process in which a liquid or solid changes to a gas. Evaporation is when particles escape the surface of a boiling liquid and enter a gas state.

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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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