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Phase Changes

Bubble, bubble, toil and trouble. Phase Changes. Boiling. Converting liquid to vapor within liquid and at surface Equilibrium vapor pressure equals atmospheric pressure Boiling point: temperature at which equilibrium vapor pressure equals atmospheric pressure. Molar Heat of Vaporization.

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Phase Changes

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  1. Bubble, bubble, toil and trouble... Phase Changes

  2. Boiling • Converting liquid to vapor within liquid and at surface • Equilibrium vapor pressure equals atmospheric pressure • Boiling point: temperature at which equilibrium vapor pressure equals atmospheric pressure

  3. Molar Heat of Vaporization • Defined: amount of energy required to convert 1 mole of liquid to solid at boiling point • Added energy does not increase temperature, but separates liquid particles • Liquid with strong attractive force has high molar heat of vaporization

  4. Freezing • Change from liquid to solid • Temperature at which liquid phase of substance is in equilibrium with solid at one atmosphere is freezing point • Freezing point = melting point • Energy loss during freezing converted to order of particles in solid

  5. Molar Heat of Fusion • Defined: amount of heat required to melt one mole of substance at normal melting point • Temperature does not change during melting • Added energy overcomes attractive forces of solid and decreases order of particles

  6. Example: Vaporization • Calculate the molar heat of vaporization of a substance if 0.433 mole of the substance absorbs 36.5 kJ energy when it is vaporized. • Known: 0.433 mole 36.5 kJ energy • Molar heat of vaporization = 36.5 kJ 0.433 mole • So ΔHv = 84.2956 kJ/mole

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