1 PHASE CHANGES: Chap. 13: Day 4 Heat of Fusion Heat of Vaporization Phase Diagrams

2 Heating/Cooling Curve  temperature =  KINETIC E  phase (position) =  POTENTIAL E Used to show the Energy changes associated with changes in phase Why do the two phase changes take different amounts of energy?

3 Enthalpy (kJ/ mol) Heat of Fusion Heat of Vaporization

4 PHASE CHANGES: Standard molar enthalpy of Fusion = (kJ/mol)   fus The heat energy required to fuse (melt) one mole of a sample

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6 PHASE CHANGES: Standard molar enthalpy of Vaporization = (kJ/mol)  H  vap The heat energy required to vaporize one mole of a sample

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8 1.You place 985 g of water (1L) into a pan at 100 C. How much heat must be supplied to vaporize all the water? 2.The same amount ice is at 0 C. How much heat must be supplied to melt all the water?

9 TWO ways to change PHASE Temperature Pressure

10 Al melting points

11 Boiling points: Liquid to Vapor Water

12 Phase Diagrams

13 TRANSITIONS BETWEEN PHASES Section Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line. (At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, for example.)

14 Phase Equilibria — Water Solid-liquid Gas-Liquid Gas-Solid

15 And deposits when cooled

16 Triple Point — Water At the TRIPLE POINT all three phases are in equilibrium.

17 Phases Diagrams— Important Points for Water T(˚C)P(mmHg) Normal boil point Normal freeze point0760 Triple point

18 Critical T and P Above critical T no liquid exists no matter how high the pressure. As P and T increase, you finally reach the CRITICAL T and P

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20 Critical T and P T c ( o C) P c (atm) M ( g/mol ) T c ( o C) P c (atm) M ( g/mol ) H 2 O (18) P Freon (121) NP (CCl 2 F 2 ) CO (44) NP CH (16) NP Notice that T c and P c depend on intermolecular forces.

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23 Phase Diagram for Water

24 Solid-Liquid Equilibria Raising the pressure at constant T causes water to melt. The NEGATIVE SLOPE of the S/L line is unique to H 2 O. Almost everything else has positive slope.

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