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

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 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

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

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

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