Vapour pressure of water at 100°C is___________________?
Correct answer: B. 760 mm Hg
- A. 55 mm Hg
- B. 760 mm Hg
- C. 355 mm Hg
- D. 1489 mm Hg
Explanation
At 100°C, water boils at normal atmospheric pressure because its vapour pressure equals 1 atmosphere, which is 760 mm Hg. Students may choose another numerical value by confusing vapour pressure with pressure at a different temperature or with the pressure above a non-boiling liquid.
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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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