C121 11-3 lec32GL

C121 11-3 lec32GL - Lecture 32 Intermolecular Forces Last...

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Lecture 32 November 25, 2010 Intermolecular Forces Last Day: Intermolecular Forces (Chapter 16) Physical Properties Predicting Physical Properties Trends in Physical Properties Vapour Pressure Today: Intermolecular Forces Vapour Pressure Temperature Dependence of Vapour Pressure Phase Diagrams
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Predicting Physical Properties 1. 2. knowledge of intermolecular forces allows us to predict physical properties when comparing compounds /atoms identify all intermolecular forces present in each identify the relationship between the strength of the intermolecular force(s) and the physical property in question ie. high b.p. requires strong IMF low viscosity requires weak IM F
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II. The boiling points of the covalent hydrides of elements in Groups 4A, 5A, 6A, and 7A. Tetrahedral non-polar dispersion dominates Steady increase in b.p. with molar mass All polar covalent dispersion and dipole-dipole N.B. electronegativity values change little down a group observed changes due to dispersion NH 3 , HF,H 2 O do not follow trend strong hydrogen bonding
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Vapour Pressur e (P vap ) the pressure exerted by a gas in dynamic equilibrium with its liquid (or solid) at a particular temperature in a closed container as time passes initially at equilibrium
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The rates of condensation and evaporation over time for a liquid sealed in a closed container.
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The vapour pressure: 1. 2. is an intensive property which means it is independent of the amount of liquid/solid presen t ie. vapour pressure has a fixed value for any amount of a pure substance at a given temperature P vap (H 2 O (l) ) = 23.756 torr at 25°C P vap (H 2 O (l) ) = 149.4 torr at 60°C is i nversely proportional to the strength of the inter- molecular forces in the liquid or solid phase Strong IMF Low P vap Weak IMF High P vap
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(i) volatile liquids (those that evaporate readily at ordinary temperatures) have weak IMF and high P vap ex. both
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This note was uploaded on 12/10/2011 for the course CHEM 121 taught by Professor Leech during the Fall '11 term at Simon Fraser.

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C121 11-3 lec32GL - Lecture 32 Intermolecular Forces Last...

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