lecture 01_14_10

# lecture 01_14_10 - Today Phase Changes and...

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1 01-14-10 Today Phase Changes and Enthalpies (12-1/2/3) Vapor Pressure and Clausius-Clapeyron equation (12-2) Phase Diagrams Structure of Solids (12-7/8) Tuesday (01-19-10) Chapter 13 (Solutions): Terminology (solute, solvent, solution) concentration units Phase Transitions sublime solid liquid gas melt solidify T M T B condense boil T S condense Dynamic Equilibrium Phase transitions consume/release heat ( Δ H!) Phase transitions depend on temperature and pressure!

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2 Enthalpies of Physical Change Vaporization: Δ H vap [kJ/mol]: heat needed to change liquid to vapor q vap = n Δ H ° vap = n(H gas –H liquid ) Example: Evaporating Water or Liquid Nitrogen Fusion: Δ H fus [kJ/mol]: heat needed to change solid to liquid q fus = n Δ fus = n(H liquid –H solid ) Example: Melting Ice Sublimation: Δ H vap [kJ/mol]: heat needed to change solid to gas. q sub = n Δ sub = n(H gas –H solid ) Example: Subliming Dry Ice Standard fusion and vaporization enthalpies for various substances symbol: Δ H ° [kJ/mol] measured at 1 atm =1.01325 x 10 5 pa and for 1 mole of pure substance
3 Additive nature of enthalpies (Enthalpy is a state function) ⎯→ Δ H Δ H ⎯→ Δ H solid liquid gas WATER ICE WATER VAPOR ICE Δ H sub = Δ H fus + Δ H vap Δ H reverse = Δ H forward At high altitude, where the pressure is low, ice does not thaw, but it just sublimes The heating curve of water • Energy “relaxes” molecule – molecule interactions • T varies before and after phase-change • T is constant during phase-change • Calculate total heat q from C p , C sp , Δ fus and Δ H ° vap

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4 Example Calculate the total heat needed to convert 18 g (1 mol) of ice at - 25 °C to vapor at 125 °C. cp
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## This note was uploaded on 02/16/2010 for the course CHEM 35991 taught by Professor Osterloh during the Spring '10 term at UC Davis.

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lecture 01_14_10 - Today Phase Changes and...

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