notes5 - Unit 5 KMT and Gases The Kinetic Molecular Theory...

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Unit 5 – KMT and Gases The Kinetic Molecular Theory The state of a substance at room temperature depends upon the strength of attraction among its particles. State Arrangement Motion Shape Volume imf’s Solid very close vibrate in place definite definite very high Liquid close flow over and around each other indefinite definite high Gas very far apart random motion indefinite indefinite none Phase changes: Melting: solid à liquid absorbs energy, +E Freezing: liquid à solid releases energy, -E Vaporization: liquid à gas absorbs energy, +E (boiling) Condensation: gas à liquid releases energy, -E Sublimation: solid à gas absorbs energy, +E (dry ice) Deposition: gas à solid releases energy, -E (frost) Phase Diagram: a graph of pressure vs. temperature that shows the conditions under which the phases of a substance exist. Each pure substance has a unique phase diagram, although most have the same basic shape. Each has three lines that delineate the equilibria between the phases. Most phase diagrams have these characteristics: 1) Triple Point: a point (specific pressure & temperature) at which all three phases coexist in equilibrium. The triple point of a pure substance distinguishes it from other substances. (Point A) 2) Critical Point: a point (specific pressure & temperature) at which the liquid and vapor phases of a substance are indistinguishable (identical) (Point C) 3) Normal Freezing Point: the temperature at which solid and liquid are in equilibrium at standard pressure (1atm) (Point E) 4) Normal Boiling Point: the temperature at which liquid and gas are in equilibrium at standard pressure (1atm) (Point F) 5) Sublimation Curve:H 2 O(s) H 2 O(g) à Line BA; solid above, gas below 6) Melting Curve: H 2 O(s) H 2 O(l) à Line AD; solid on left, liquid on right 7) Vaporization Curve: H 2 O(l) H 2 O(g) à Line AC; liquid on left, gas on right Drawing a Phase Diagram: the necessary data to sketch a phase diagram for a pure substance are: Triple Point Critical Point Vapor Pressure of the solid or liquid at standard pressure The relative densities of the solid and liquid (to set the angle of the melting curve) Phase diagram for water Intermolecular Forces (imf’s): Weak forces of attraction between molecules; collectively known as van der Waals forces; listed in basic order of strength from strongest to weakest Dipole-dipole force (polar-polar) example: HCl Higher melting point than expected Substances mostly solids or liquids Chip Shea 1 11/5/2011
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Hydrogen bonding Special dipole-dipole force occurring between ‘H’ of one molecule and either ‘O’, ‘N’, or ‘F’ of another molecule. H-bonds give water its unusual properties- ice floats, high mp and bp, high surface tension. Dipole-Induced dipole (polar-nonpolar)example: I
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This note was uploaded on 11/05/2011 for the course ECON 101 taught by Professor Graham during the Spring '08 term at N. Colorado.

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notes5 - Unit 5 KMT and Gases The Kinetic Molecular Theory...

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