chapter11.part2.2008.forBB

# chapter11.part2.2008.forBB - Chapter 11 Liquids Solids and...

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1 1 Chapter 11: Liquids, Solids and Materials Part 2 2 Clausius-Clapeyron Equation The normal bp of water = 100°C and Δ H vap = 40.71 kJ/mol. At what T will water boil if P = 500 Torr? ln = P 2 P 1 1 T 2 1 T 1 - Δ H vap R ln = 500 760 1 373 1 T 2 - 40710 J g -1 8.315 J K -1 mol -1 - 0.4187 = - 4896.3 - 2.681 x 10 -3 1 T 2 T 2 = 361 K = 88 °C = 190 °F

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2 3 Life at high altitude What is the temperature of boiling water in a camp at the peak of Mt. Everest? (9000m, 25 kPa) 4 Pressure cookers increase the H 2 O bp
3 5 What P is needed to return the boiling point to 100°C at the peak of Mt. Everest? A: 188 torr B: 532 torr C: 760 torr D: 875 torr 6 Melting and Freezing The molecules in a solid are closely packed and in constant motion. They ± vibrate about fixed positions ± do not do not have enough E to slide past each other. A solid melts when E k > forces holding the particles in their fixed positions. Melting is endothermic . Freezing Freezing (solidification, crystallization) is exothermic exothermic .

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4 7 Phase Changes Δ fus = = Δ cryst cryst Molar heat of crystallization, Molar heat of crystallization, Δ cryst Heat released when 1 mol crystallizes ( P = 1 bar). For H 2 O(s) H 2 O( l ) Δ = Δ fus = +6.02 kJ/mol For H 2 O( l ) H 2 O(s) Δ = Δ cryst = -6.02 kJ/mol Normal Normal melting or freezing occurs at P = 1 atm Molar heat of fusion, Molar heat of fusion, Δ fus fus Heat required to melt 1 mol ( P = 1 bar). 8 Phase Changes Sublimation – the direct conversion of a solid to a gas Examples Solid CO 2 (dry ice) sublimes. Ice (v.p. = 4.6 mmHg @ 0°C) in a frost-free ‘fridge is removed by blowing dry air over it… Deposition Deposition is the reverse process: (g) (s) Example : plating A l onto the surface of a CD Δ sub sub = = Δ dep dep
5 9 Phase Changes endothermic process (heat added) exothermic process (heat released) 10 Phase Changes

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6 11 Phase Changes Substance mp(°C) Δ H fus (kJ/mol) bp(°C) Δ H vap (kJ/mol) O 2 (16 e - ) –248 0.445 –183.0 6.8 F 2 (18 e - ) –220 1.020 –188.1 6.54 C l 2 (34 e - ) –103 6.406 –34.6 20.39 Br 2 (70 e - ) –7.2 10.794 59.6 29.54 Nonpolar molecules London forces increase as the number of e - increase. The data support this trend… 12 Phase Changes Substance mp(°C) Δ H fus (kJ/mol)* bp(°C) Δ H vap (kJ/mol)* SO 2 (32 e - ) –76 7.4 –10.0 24.9 HC l (18 e - ) –115 2.0 –85.1 16.2 HBr (36 e-) –87 2.4 –66.8 17.6 H 2 O (10 e - ) 0 6.0 +100.0 40.7 HF (10 e - ) –83 4.6 +19.5 7.5 NH 3 (10 e - ) –78 5.6 –33.5 23.4 Polar molecules More difficult to explore trends. Values depend on London, dipole forces and H-bonding.
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chapter11.part2.2008.forBB - Chapter 11 Liquids Solids and...

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