4. (a) For a pure substance with a normal freezing curve, is the liquid or solid

Question

4.   (a) For a pure substance with a normal freezing curve, is the liquid or solid state more stable for a sufficient isothermal increase in pressure? Which phase would be favored if the substance was anomalous?

      (b) If the triple point of water occurs at exactly 0.01 degrees Celsius and the vapor pressure of the liquid at this temperature is 4.585 mmHg, find the vapor pressure of ice at 0.01 degrees Celsius.

      (c) Which has the higher vapor pressure at -20 degrees Celsius, ice or supercooled water?

Explanation / Answer

4 (a) The solid state will be more stable because it implies a reduction in the molar volume. For an anomalous substance (as water) the liquid phase is favoured with the increase in pressure because the liquid phase occupies a smaller molar volume.

(b) the vapor pressure is exactly the same (4.585 mmHg) because at triple point coexist the liquid, solid and gas phase by definition.

(c) supercooled water has the higher vapor pressure because even if it is at -20 oC as the ice, it has more kinetic energy to pass to the gas phase than molecules in the ice water phase.

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