LIQUIDS AND SOLIDS - Properties of Liquids and Solids...

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•1 CHEM 1000 3.0 Structure of liquids and solids 1 Properties of Liquids and Solids Petrucci, Harwood and Herring: Chapter 12 Aims: To use the ideas of intermolecular forces to: –Explain the properties of liquids using intermolecular forces –Understand the relation between temperature, pressure and state of matter –Introduce the structures of solids CHEM 1000 3.0 Structure of liquids and solids 2 Vaporization of Liquids • In gases we saw that the speed and kinetic energies of molecules vary, even at the same temperature. • In the liquid, some molecules will always have sufficient kinetic energy to overcome intermolecular forces and escape into the gaseous state. • This is vaporization . The enthalpy required for vaporization is the heat of vaporization Δ H v . Δ H v = H vapour – H liquid = - Δ H condensation CHEM 1000 3.0 Structure of liquids and solids 3 • Molecules can escape from the liquid into the vapour. • Gas phase molecules can condense into the liquid. • An equilibrium is set up between evaporation and condensation. • The result is that there is constant partial pressure of the vapour called the vapour pressure. • This will be a strong function of temperature. Vaporization of Liquids
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•2 CHEM 1000 3.0 Structure of liquids and solids 4 Vapor Pressure Liquid Vapor vaporization condensation CHEM 1000 3.0 Structure of liquids and solids 5 Determining Vapour Pressure • Vapour pressures usually determined by allowing a liquid to come into equilibrium with its vapour and using the ideal gas law to determine the equilibrium pressure. CHEM 1000 3.0 Structure of liquids and solids 6 Vapour pressure curves for: (a) Diethyl ether, C 4 H 10 O; (b)benzene, C 6 H 6 ; (c) water; (d)toluene, C 7 H 8 ; (e) aniline, C 6 H 7 N.
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•3 CHEM 1000 3.0 Structure of liquids and solids 7 Temperature Dependence of Vapour Pressure B T A ln(P) + - = CHEM 1000 3.0 Structure of liquids and solids 8 Temperature Dependence of Vapour Pressure • From thermodynamics we can show that A = Δ H vap /R • The equation is usually expressed in terms of two temperatures to give the Clausius- Clapeyron equation. - Δ = - Δ - = 2 1 1 2 1 2 1 2 1 1 ln or 1 1 ln T T R H P P T T R H P P vap vap CHEM 1000 3.0 Structure of liquids and solids 9 Boiling and Boiling point • Suppose vaporization occurs in the bulk liquid. – A bubble of vapour forms • If the vapour pressure is less than the external pressure the bubbles will collapse. • If the vapour pressure is equal to or greater than the external pressure the bubbles will rise to the surface and escape. • This is boiling, and the temperature is the
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This note was uploaded on 08/08/2009 for the course CHEM CHEM 1000 taught by Professor Marzad during the Summer '09 term at York University.

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LIQUIDS AND SOLIDS - Properties of Liquids and Solids...

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