04CHM114_0331

04CHM114_0331 - CHEM 114 32004 Wednesday Mar 29th Lecture...

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Unformatted text preview: CHEM 114 32004 Wednesday Mar 29th Lecture 'No. 26 I " CHAPTER 11. (Cont’d) INTERMOLECULAR FORCES, LIQUIDS AND SOLIDS. (Preparing us for materials chemistry) The viscosity of liquids and the formation of glasses. solid polymers. fluidity = (viscosity) ‘1 mercury vs road pitch , FLUIDITY :Variation with temperature, “ fluidity ex 9.5.3 Cd» 1‘ Temperature glass transition (No AV) volume glasses and medieval cathedral windows ‘vapor pressure: the pressure of the gas that exists in equilibrium with a liquid containing the same molecules. win-POO V EXPONENTIAL increase with T compare with ideal gas behavior P in. ft. tad @- HOW TO MAKE A “beautiful? STRAIGHT LINE OUT OF VAPOR PRESSURE vs T? log p _ III- NLT 1/T ( s w 1- Why is it straight?. . .. because probability of a molecule escaping across surface and gaining AHv/NAVV in energy is a Boltzmann function of T Boltzmann function p = p0 e exp(-E/RT) take (natural) logs of both sides E = energy gap to be crossed RT = available energy in the surroundings lnp =lnp 3 AH/RT 0 V so lnp vs IfT should be a straight line. The slope gives the value of AHv/R So here is a way that scientists can find the latent heat of boiling and get a measure of the intermolecular forces Without ever boiling the liquid. Melting phenomenon: equilibrium between crystal and liquid normal melting poin ' mnormal case) 9",, . PRESSURE Phase Diagrams for pure substances (sec 11.6) The phase diagram (phase equilibrium diagram) is a way of summarizing what we know about the conditions of P,T, under which liquid, gaseous and crystal states of a substance are stable. Note'vapor pressure of solid (crystal) The points to make are: 1. areas on the graph are the important thing. What was a plot of vapor pressure vs T before is 5 now a line separating stable P,T regions of liquid from stable P,T regions of gas. (see Fl g. 11.26: 2. Boiling 3. How to proceed from the liquid state to the gas without ever seeing boiling. WtFI—E _ Wgufi C nab“ r 4. The trig 1e 12 oint, and latent heat relations there Mk, + AH,“ = AHS (The meaning of two-phase and three-phase "equilibrium": Exchange rates across surface of liquid and of solid must be, on average, the same). Examples of phase diagrams for specific substances. 1. Water Fig. 11.27 LH panel 2. carbon dioxide Fig. 11. 27 (RH panel) «M ' a, Mu 9‘ Lu A-‘t-ee 3. The meaning of two-phase and three— phase "equilibrium". (Exchange rates across surface of liquid and of solid must be, on average, the same). TWO SECIAL CASES (Fig. 11.25) 1. Water (backward slope of melting curve) 2. Carbon dioxide (Triple point above 1 atm. Therefore solid sublimes on heating at 1 atm press. Liquid only if P > 5.11 atm. THE SOLID STATE 1. CRYSTAL STRUCTURES (a) The crystal lattice concept, and the unit cell. 8'1 VG'GK‘H; ¢ ‘55:" u! ' a“ build up Uh“ u. I Mount“ ' 6.4 (b) The seven symmetry c asses for crystals P“ .’ Variables are: . an 5 u. 2 kit-Vt. 1:9. Q¢L L‘Ifi 40' m (c) the alternative packings of spheres Within the cubic system (simple cubic, body-centered cubic, face . 1 1.31-33 Simple cubic BCC Mai? (bcc, fcc, hcp ) L’ M‘fitsoul C46“. Mani, Sam; %€\¢Lc~1 «.4 F51: _ iron has two..see below ...
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04CHM114_0331 - CHEM 114 32004 Wednesday Mar 29th Lecture...

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