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CH. 12 INTERMOLECULAR FORCES

CH. 12 INTERMOLECULAR FORCES. Phases, phase changes Liquids, Solids Trends. Equations. Clausius-Claperyron. RECALL. 3 physical states solid -- liquid -- gas. condensed phases. Phase change related to: intermolecular forces + KE. Chemical behavior in diff phases -

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CH. 12 INTERMOLECULAR FORCES

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  1. CH. 12 INTERMOLECULARFORCES Phases, phase changes Liquids, Solids Trends Equations Clausius-Claperyron

  2. RECALL 3 physical states solid -- liquid -- gas condensed phases Phase change related to: intermolecular forces + KE Chemical behavior in diff phases - same Physical behavior in diff phases - diff WHY????? Due to strength of inter- forces PE depends on (Coulomb’s) *charges of particles; dist bet KEspeeda absol. T

  3. GAS - no attraction (far apart); random; highly compress; flow/diffuse ezly LIQUID - some attraction (contact); random; not compress; flow/diffuse slower SOLID - strongest attraction (fixed position); not compress; flow/diffuse not Phase Changes gas -------> liq condensation (exo) (endo) vaporization <------- liq --------> solid freezing (exo) (endo; fusion) melting <------- T 12.1 pg 420

  4. Enthalpy Change DHovap DHofus H2O (l) ------> H2O (g) DH = DHovap = 40.7 kJ/mol DH = DHovap = -40.7 kJ/mol <---------- E wise? DHovap >DHofus recall, dist & motion fig 12.2, pg 421 fig 12.3, pg 422

  5. TEMP DHovap DHofus Heat Flow Out removed ----------> COOLING CURVE Shows changes that occur when add/remove heat @ const T fig 12.4, pg 423 GAS GAS-LIQ LIQUID SOLID LIQ-SOLID GAS-LIQ: const T & EKE ave speed is same at given T decr ave EPE but not D EKE H2O (g) & H2O (l) same EKE liq EPE < gas EPE @ same T; heat released = moles * (-vap) q = n*(-DHovap) GAS: q = n*Cgas*DT results in largest amt of heat released WHY??? decr PE due from condensing dist. bet molecules

  6. LIQUIDq = n*Cliq*DT * loss of heat results in decr T decr molecular speed, this decr EKE LIQ-SOLID * inter- attraction > motion of molecules * loss EPE form crystalline solid * const T & EKE * H2O (l) & H2O (soln) same EKE solid EPE < liq EPE @ same T; heat released = moles * (-fusion) q = n*(-DHofus) SOLID q = n*Csol*DT motion restricted; decr T reduced ave speed TOTAL HEAT RELEASED Use Hess’ Law sum of 5 steps 2 pts @ const P w/i phase: Dq is DT (DEKE) depends on: amt subst (n), C for phase, DT during phase D: Dq (@T)(DEPE), dist bet molecules changes

  7. LIQ-GAS EQUILIBRA @ const T open closed vaporize condense Sys reaches pt of dynamic balance @ equilibria, (rate condensation = rate vaporization) then vp const Keep in Mind: when a sys at equil is distr, Sys will react in way to counteract said disturb to regain a state at a new equilib Weaker bonds = higher vp,lower bp

  8. VP - depends on T, inter- forces effects of incr T: incr n to vaporize, decr amt condense higher T -- higher vp SOLID - strongest attraction (fixed position); not compress; flow/diffuse not Universal Gas Const R = 8.31 J/mol-K Hold 3 variables const, vary 1, can find 4th Clausius - Clapeyron Eqn

  9. At 34.10C, vpH2O = 40.1 torr. Find the vp @ 88.50C. DHvap = 40.7*103 N-m 1 N-m = 1 J P1 = 40.1 torr T1 = 273.15 + 34.1 = 307.25 K T2 = 361.65 K P2 = 10.99889*(40.1 torr) = 441 torr Talked about bp - What exactly is bp?

  10. SOLID - LIQ EQUILIBRA -As a solid - vibrate @ fixed position -incr T results incr vibration, then @ min KKE melting begin No D in compress, DP no effect DP effects bp but not mp SOLID - GAS EQUILIBRA: Sublimation Solids decr vp < liq Solids: high vp Phase Diagrams???

  11. From the data: bp = 78.5oC DHvap = 40.5 kJ/mol cgas = 1.43 J/g-oC cliq = 2.45 J/g-oC At constant P (1 atm), how much heat needed to convert 0.333 mol of ethanol gas at 300oC to liquidfy at 25.0oC 3 steps: gas; gas-liq; liq CH3CH2OH: 46.0 g/mol 1st: find mass: ______ g Cooling vapor to bp: q = Cgas*mass*DT Condensation (*direction) q = n*(-DHcond) Cooling liquid to 25.0oC q = Cliq*mass*DT Total q = qvapor+qcond+qliq

  12. A liquid has a VP of 641 torr at 85.2oC, and bp of 95.6oC at 1 atm. Calculate DHvap. At bp: ext P = VP use Clasius-Clapeyron eqn 1st: convert 641 torr to atm 2 points: P1 = ___ atm T1 = _______ K P2 = ____ atm T2 = _______ K

  13. INTERMOLECULAR FORCES Bonding Ionic --- Covalent --- Metallic Nonbonding (inter-) Ion-Dipole, H-bonding, Dipole-Dipole, (London) Dispersion attraction bet molecules due to partial charges Bond Length: shorter; dist bet nuclei 2 bonded atoms Covalent radius = (bond length)/ 2 van der Waals dist: longer; dist bet 2 nonbonded atoms VDW radius = VDW dist/ 2 incr: down col, across row

  14. O H H O H H O H H O H H O H H O H H O H H O H H O H H Cl-1 Na+1 - + - + - + + - - + Ion attracted to polar molecule ex. NaCl in H2O ION - DIPOLE DIPOLE - DIPOLE Polar vs Non higher bp More E to overcome forces -- higher bp

  15. O H H O H H .. H N H H .. .. .. .. .. Cl F C H H .. .. .. .. .. H - BONDING special Dip-Dip when H bonded to small size, high EN atom w/ unbonded e- pair plays imprt role in biological sys Criteria molecule 1: H bonded to O, N, or F molecule 2: unbonded e- on O, N, or F result: H on molecule 1 interact w/ unbonded e- on molecule 2 H2O - H2O NH3 - CH2FCl

  16. CH3 CH CH3 O-H CH3 CH CH3 O-H .. H--Br .. .. .. .. H--F .. .. .. .. .. H - BONDING HF - HBr CH3CH(OH)CH3 - CH3CH(OH)CH3 NO bonding present does not agree to the definition

  17. .. - - + + .. .. Ar .. .. .. .. .. Ar .. .. .. Ar .. DISPERSION (LONDON) FORCES only force bet NP molecules caused by momentary movement of e- charge in atoms are present bet all particles NONPOLAR overall: equal distr of e- charge - polarity cancels (average) actual: e- movement at any moment causes e- density to be conen at one end creating instantaneous dipole. Not permanent will change

  18. higher b.p. Type molecular bonding CH3Br -- CH3F CH3CH2CH2OH -- CH3CH2OCH3 C2H6 -- C3H8 dipole - dipole H-bonding dipole-dipole London CH3Br CH3CH2CH2OH C3H8

  19. Which has a lower boiling pt in each pair NH3 -- PH3 NaBr -- PBr3 H2O -- HBr PH3, dipole-dipole forces weaker, as stronger H-bonding w/ NH3 PBr3, dipole-dipole forces, as NaBr stronger ionic bonding HBr dipole-dipole forces weaker than H-bonding in water

  20. PROPERTIES OF LIQUIDS Surface Tension @ surface molecules attracted only downward (no molecules above), so need KKE to break thru surface stronger forces > surface tension Capillarity liq rises in small space against pull of gravity; forces acting bet cohesive (w/i liq) & adhesive forces Viscosity resistancce to flow, inter- attraction slow liq movement incr T -- decr viscosity stronger inter- > higher visc depends on: T & shape of molecule larger molecules higher visc long shape higher visc than small round shape (thnk of contact)

  21. SUMMARY CH. 12 Clausius-Claperyron EQUILIBRA q = n*CPHASE*DT gas -------> liq condensation (exo) (endo) vaporization <------- liq --------> solid freezing (exo) (endo; fusion) melting <------- COOLING CURVE INTERMOLECULAR FORCES bond type; bp/mp higher/lower

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