Chapter 11

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Department
Chemistry & Chemical Biology
Course
CHEM 1214
Professor
Thomas Gilbert
Semester
Spring

Description
Lecture 1 (1/7/2013) • Vapor Pressure: o Vapor Pressure:  Pressure exerted by a gas in equilibrium with its liquid.  Rates of evaporation and condensation are  equal.  PV = nRT  P = nRT / V   Generally, vapor pressure of solution is lower than vapor pressure  of pure solvent.  Number of particles affect vapor pressure (type of particles does  not matter) • Factor Affecting Vapor Pressure o Temperature:  Higher temperature = higher kinetic energy; more molecules with  sufficient kinetic energy to overcome attractive forces in liquid  phase. o Intermolecular Forces:  Must be overcome for molecules to leave the liquid and enter gas  phase.  Review of the types and relative strengths • Vapor Pressure of Solutions: o Raoult’s Law:  vapor pressure of solution is proportional to  mole fraction of  solvent (w. non­volatile solute).  P solutionsolvesolvent o Vapor Pressure Lowering: one of the colligative properties of solutions o Ideal Solutions: solutions that obey Raoult’s Law • Vapor Pressure vs Temperature: o Normal boiling point: the temperature at which the vapor pressure of a  liquid equals 1 atm (760 mmHg).  o  Clausius­Clapeyron Equation: ΔH vap 1  ln P)vap = −   + C  R  T   Plot of ln(P) vs 1/T yields  straight line: • Slope = −ΔH vap • Intercept = constant o For a given liquid at two different temperatures:  P vap,1  ΔH vap  1 1  ln =  −   P vap,2  R  T 2 T1   Lecture 2 (1/9/2013) • Fractional Distillation: o Process to separate volatile components of a mixture. o Vapor phase enriched in more volatile component:  As vapor condenses, evaporates again, achieve greater enrichment.  Ideally, separate and collect pure components.   • Solutions of Volatile Components: o For mixtures containing more than one volatile component:  Partial pressure of each volatile component contributes to total  vapor pressure of solution.  PtotalX 1 1 + X2P 2 + X3P3° …
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