Phase Chemistry. Phase Diagrams and IMF s. Copyright John Sayles 1

C-C Eq n and Phase Diagrams Graph the T and P points that solve the C-C eq n A curve Each point represents a BP The curve is the boundary between liq and gas Similar lines exist for the boundary between solid and liquid (all MP s), and solid and gas (all SP s) Combination of the 3 curves gives phase diagram for the substance Copyright 2003 - John Sayles 2

Phase Diagram Each point on a phase diagram represents a Temp and Pressure at which two phases are at equilibrium The solid-liquid equilibrium line are all MP s The liquid-vapor equilibriium line are all BP s The solid-vapor equilibrium line are all SP s The triple point is the T and P at which all three phases are at equilbirum (eg., boiling ice water) The liq-vap eq line is a C-C plot The liq-sol eq line is nearly vertical Pressure has little effect on MP Copyright 2003 - John Sayles 4

Pressure (atm) Phase Diagrams for Carbon Dioxide (Not to Scale) 11_12a Critical point (31ºC, 73 atm) Solid Liquid Gas 1.0 Triple point ( 57ºC, 5.1 atm) 78ºC Temperature A Copyright Houghton Mifflin Company. All rights reserved 11-12A Copyright 2003 - John Sayles 5

Things to do with a Phase Diagram Identify key points Triple point - all 3 phases at eq. Critical point - T beyond which no amount of pressure will condense the gas nbp and nmp - points on the liq-vap and sol-liq boundries at 1 atm pressure Predict phase changes (including sublimation) As T changes (at constant P) As P changes (at constant T) Decide whether sol or liq is more dense Based on tilt of liq-sol eq line Copyright 2003 - John Sayles 6

Pressure (atm) Phase Diagram for Water (Not to Scale) 11_11 B (374º C, 218 atm) C Solid Liquid Gas 1.0 D A (0.01ºC, 0.00603 atm) 0ºC 100ºC Temperature Copyright Houghton Mifflin Company. All rights reserved 11-11 Copyright 2003 - John Sayles 7

Phase Diagram practice Identify the triple point, nmp, nbp and critical point for water Consider water vapor at -1 C and -30 atm. What would happen if P increased at const. T? Consider water vapor at 380 C and 1.0 atm. What would happen if P increased at const. T? Consider ice at -20 C and 1.0 atm. What would happen if T increased at const. P? (with CO 2?) Consider ice at -1 C and 0.005 atm. What would happen if P increased at const. T? Which is more dense, ice or water? Copyright 2003 - John Sayles 8

Strange Properties of Water Solid is less dense than liquid (eq line tilts left) Water expands as it freezes Damages pipes, roads, cells, car engines Makes ice skating possible Pressure under skate blade temporarily melts ice Ice floats Makes life on earth possible All because of the inefficient packing in the ice crystal Copyright 2003 - John Sayles 9

Pressure (atm) Monoclinic Phase Diagrams for Sulfur (Not to Scale) 11_12b Triple point (151ºC, 1290 atm) Rhombic Liquid Triple point (119ºC, 6 X 10 5 atm) Gas Triple point (95ºC, 1 X 10 5 atm) Temperature B Copyright Houghton Mifflin Company. All rights reserved 11-12B Copyright 2003 - John Sayles 10

Intermolecular Forces (IMF s) There are 3 (or 4) different types of IMF London (dispersion) Forces Weakest: 0-5m kj/mol All particles have these; most important in non-polar Dipole Forces Middle: 5-10 kj/mol Only polar molecules have these Hydrogen Bonds Strongest: 10-40 kj/mol (!) In molecules that have N, O, or F attached directly to H Copyright 2003 - John Sayles 11

London Forces Caused by temporary dipoles as e - s disperse Increase with MW and molecular volume Larger MW means more e - Larger MW means e - s are more polarizable If MW s are the same, larger molecular volume increases London Forces If this is the only IMF, particles aren t held very tightly Will be volatile (possibly a gas at room temp) Low MP, BP (for a given MW) Low surface tension and viscosity Copyright 2003 - John Sayles 12

Dipole-Dipole Forces Caused by permanent dipoles (polar molecules) Molecules with polar bonds and asymmetry Larger diff in electroneg. and greater asymmetry make for a larger dipole moment Smaller size allows molecules to get closer Polar substances will be more tightly held than non-polar Less volatile Higher MP, BP Greater surface tension and viscosity Copyright 2003 - John Sayles 14

Hydrogen Bonds Found only between molecules with H attached directly to N, O, or F Extremely high performance dipole forces Coulomb s Law N, O, F are very electronegative (big partial Q) N, O, F are very small (small r) H is VERY small, especially with its e - being hogged by N, O, F Molecular velcro, especially in Biochem Low volatility, high MP, BP, surf tens, visc Copyright 2003 - John Sayles 15

Boiling point (º C) Boiling point (º C) Boiling Point versus Molecular Weight for Hydrides 11_24 120 20 H 2 O 100 0 HF 80 20 60 40 NH 3 SbH 3 HI 40 60 20 80 HCl AsH 3 HBr SnH 4 H 2 Te 0 100 PH 3 GeH 4 20 120 SiH 4 40 60 H 2 S H 2 Se 140 160 CH 4 20 40 60 80 100 120 20 40 60 80 100 120 Molecular weight A Molecular weight B Copyright Houghton Mifflin Company. All rights reserved 11-24 Copyright 2003 - John Sayles 16

Dipole-Induced Dipole Forces Found in mixtures of non-polar and polar Polar molecules repel e - s in non-polar ones Forced dispersion Between London and Dipole forces in strength Copyright 2003 - John Sayles 18

Properties of Liquids Relate each of the following to IMF s and MW Volatility Increases with low IMF s, low MW MP, BP Increase with high IMF s, high MW Surface Tension Increases with high IMF s Decreased by soaps and detergents (surfactants) Viscosity Increases with high IMF s, high MW Multi-viscosity additive in oil is rolled up at low T, uncoils and restricts flow at higher T Copyright 2003 - John Sayles 19

Properties of Some Liquids at 20 C T11_3 Substance Molecular Weight (amu) Vapor Pressure (mmhg) Surface Tension (J/m 2 ) Viscosity (kg/m s) Water, H 2 0 Carbon dioxide, CO 2 Pentane, C 5 H 12 Gl cerol, C 3 H 8 O 3 Chloroform, CHCl 3 Carbon tetrachloride, CCl 4 Bromoform, CHBr 3 18 44 72 92 119 154 253 1.8 x 10 1 4.3 x 10 4 4.4 x 10 2 1.6 x 10-4 1.7 x 10 2 8.7 x 10 1 3.9 x 10 0 7.3 x 10-2 1.2 x 10-3 1.6 x 10-2 6.3 x 10-2 2.7 x 10-2 2.7 x 10-2 4.2 x 10-2 1.0 x 10-3 7.1 x 10-5 2.4 x 10-4 1.5 x 10 0 5.8 x 10-4 9.7 x 10-4 2.0 x 10-3 Copyright Houghton Mifflin Company. All rights reserved Table 11.3 Copyright 2003 - John Sayles 20

Molecular Solids Particles are molecules Particles held by Intermolecular Forces Dispersion forces, dipole-dipole forces, H-bonding Properties Low MP, low BP, poor thermal and electrical conductivity Solubility depends on polarity Examples H 2 O, CO 2 Copyright 2003 - John Sayles 21

Network Covalent Solids Particles are atoms Particles are held by covalent bonds Properties Very hard, very high MP and BP, poor thermal and electrical conductivity Not soluble in any solvent Examples C (diamond), C (graphite), SiO 2 (quartz) Copyright 2003 - John Sayles 22

Ionic Solids Particles are ions Particles are held by electrostatic attractions dependent on the charge and radius of the ions Properties Hard & brittle, high MP and BP, poor thermal and electrical conductivity in solid, good conductors as melts and solutions Soluble in polar solvents Examples NaCl, CaCO 3, AlCl 3 Copyright 2003 - John Sayles 24

Metallic Solids Particles are cations in a sea of e - s Particles are held by electrostatic attractions Properties Variable hardness, variable MP and BP, good conductors in solid and melt, not soluble Examples Hg (l), Pb, Ti Copyright 2003 - John Sayles 27