A. Phase Changes Sublimation solid  gas v.p. of solid equals external pressure EX: dry ice, mothballs, solid air fresheners

B. Phase Diagrams Show the phases of a substance at different temps and pressures

Water vs. Carbon Dioxide B. Phase Diagrams Water vs. Carbon Dioxide

C. Heating Curves Gas - KE  Boiling - PE  Liquid - KE  Melting - PE  Solid - KE 

C. Heating Curves Temperature Change change in KE (molecular motion) Phase Change change in PE (molecular arrangement) temp remains constant

C. Heating Curves Heat of Fusion (Hfus) energy required to melt or freeze 1 mole of a substance at its m.p./f.p. Hfus of ice = 6.009 kJ/mol To freeze (or melt) one mole of ice, you need to remove or put in 6.009 kJ of energy (heat)

C. Heating Curves Heat of Vaporization (Hvap) energy required to boil or condense 1 mole of a substance at its b.p./c.p. Hvap for water = 40.79 kJ/mol usually larger than Hfus…why? EX: sweating, steam burns

D. Properties of Water Hfus of ice = 6.009 kJ/mol Hvap for water = 40.79 kJ/mol To calculate the amount of heat energy required to melt or freeze a substance: convert grams to moles multiply by molar heat of fusion or vaporization

D. Properties of Water How much heat energy is required to melt 25 grams of ice at 0oC to liquid water at a temperature of 0oC? ice 6.009 kJ 1 mol H2O 25 g H2O 1 mol H2O 18.02 g H2O = 8.3 kJ

D. Properties of Water How much heat energy is required to change 500.0 grams of liquid water at 100oC to steam at 100oC? steam 40.79 kJ 1 mol H2O 500.0 g H2O 1 mol H2O 18.02 g H2O = 1132 kJ