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Chemistry 177 December 2, 2009 Take out CLICKERS: “GO 41 GO” -or- “CH 41 CH” and CALCULATORS NEXT LECTURE: Friday, Dec. 4; Bring CLICKERS READ BLBM, Chapter 11 HOMEWORK #15: Ch. 10: # 32, 36, 44, 54, 58, 66 Due in Recitation, Tomorrow DCI #11: QUIZ #15: Gases (Stoichiometry, Partial Pressures, etc.) OPTIONAL EXAM: Monday, December 7, 6:30-7:30 PM (Multiple Choice) FINAL EXAM: Monday, December 14, 7-9 PM Effusion and Diffusion Chapter 10: Gases Effusion is the escape of gas molecules through a tiny hole into an evacuated space. Diffusion is the spread of one substance throughout a space or throughout a second substance. 2009, Prentice-Hall, Inc. Chapter 10: Gases Effusion and Diffusion Graham's Law KEA = KEB 2009, Prentice-Hall, Inc. Chapter 10: Gases Chapter 10: Gases Deviations from Ideal Behavior 2009, Prentice-Hall, Inc. Real Gases Chapter 10: Gases 2009, Prentice-Hall, Inc. Chapter 10: Gases Van der Waals equation “Nonideal” gas Real Gases Chapter 10: Gases Real Gases Clicker Question Chapter 10: Gases Clicker Question Chapter 11: Intermolecular Forces, Liquids, and Solids Some Experimental Observations What trends can you identify in these data? B.P. (K, 1 atm) MW (g/mol) Polarity a (L2 atm/mol2) b (L/mol) H2 20.3 2.02 Nonpolar 0.2444 0.02661 He 4.2 4.00 Nonpolar 0.0341 0.02370 N2 77.4 28.00 Nonpolar 1.3990 0.03913 O2 90.2 32.00 Nonpolar 1.36 0.03183 CO 81.7 28.01 Weakly Polar 1.485 0.03985 NO 121.4 30.00 Weakly Polar 1.340 0.02789 CO2 194.7sub 44.01 Nonpolar 3.592 0.04267 H2O 373.0 18.02 Polar 5.464 0.03049 Cl2O 277.0 70.90 Nonpolar 6.49 0.0562 Xe 166.1 131.30 Nonpolar 4.19 0.0266 Gas Chapter 11: Intermolecular Forces, Liquids, and Solids Some Experimental Observations Capillary Action Normal Boiling Points T (°C ) OH2 100 FH 0 SH2 NH3 H2O -100 Xe CH4 -200 Kr Ar He Ne -300 1 2 3 P erio d 4 5 6 Hg Chapter 11: Intermolecular Forces, Liquids, and Solids Intermolecular Forces As a gas cools, the KE of the molecules drops, and as molecules collide (or come close to one another), any attractions between them might overcome the KE and allow them to stick together. When this happens for 1023 molecules, the gas condenses. Ion-Ion forces: Interactions between two ions; repulsive between same charges, e.g., Na+Na+ or ClCl; attractive between opposite charges, e.g., Na+Cl. The strength of the attraction varies as d–1. Ionic Liquids: Melting points less than 100 C… bmim+ = (C8H15N2)+ Cl Na+ d Isotropic Interaction NaCl (mp = 800 C) Source: E.J. Maginn, U. Notre Dame Chapter 11: Intermolecular Forces, Liquids, and Solids Intermolecular Forces: Neutral molecules? Source: University of Florida, Philip Brucat Chapter 11: Intermolecular Forces, Liquids, and Solids Intermolecular Forces: Polar Molecules (Dipole Moments) q +q d + Nonpolar H2 H H Center of Molecule CO2 Polar H+ HCl Cl + “Symmetrical” O C O “Unsymmetrical” H2 O Dipole Moment = 0 H O + H Dipole Moment 0 + Chapter 11: Intermolecular Forces, Liquids, and Solids Intermolecular Forces: Polar Molecules Ion-Dipole forces: Interactions between a polar molecule and an ion, e.g., Na+ ions in water. The strength of the attraction varies as d–4. Dipole-Dipole forces: Interactions between polar molecules. Strength varies as d6. d 1 + + Isotropic d2 H2O H2O + + + + d3 + At 0°C, Br2(l) but ICl(s) Na+ 160 g/mol Anisotropic (Shape) H2O Na+(aq) Tb Liquid Gas 162 g/mol B.P. (K) (1 atm) Dip. Mom. (Debye) Heat of Vap. (kJ/mol) N2 77.4 0 5.6 O2 90.2 0 6.8 NO 121.4 0.153 13.8 CO 81.7 0.112 6.8 + + H2O Chapter 11: Intermolecular Forces, Liquids, and Solids Intermolecular Forces: Polar-Nonpolar Molecules Dipole-Induced Dipole forces: Interactions between a nonpolar molecule/atom and a polar molecule ion, e.g., Ar atoms with HCl. 1 V d H+ Cl 6 Nonpolar (Dipole Moment = 0) Induced Dipole Moment 18+ 18 Polar Molecule Ar “Polarizable” Increases with increasing size Ar < Kr < Xe Chapter 11: Intermolecular Forces, Liquids, and Solids Intermolecular Forces: Nonpolar-Nonpolar Molecules Dispersion (van der Waals) forces: Attractive forces arising when temporary dipole moments are induced in molecules due to the electrostatic interactions with adjacent molecules. These forces increase with molar mass because the number of electrons also increases and the size increases. For nonpolar molecules, these are the essential forces that lead to condensation of the gas to 6 a liquid or solid: noble gases, CO2, N2, O2, CH4, C4H10, …. 1 V d 18 18+ 18+ Ar + 18 Ar +