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lec5_whc - Review of Last Lecture ch 12 Liquids Solids and...

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Review of Last Lecture ch. 12: Liquids, Solids and Intermolecular Forces Surface Forces and wetting • Viscosity Vapor Pressures Simple phase diagrams
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Surface tension γ : the energy required to increase surface area of liquid. Chapter 12: Properties of Liquids Floating needle. Cohesive Forces
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Vapor Pressure Vapor pressure : gas pressure above liquid ( volatile Æ lots) Leave an open glass of water at room T ? “Dynamic equilibrium” – always some vapor liquid vapor
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Mercury barometer Vapor pressure of liquid P vap independent of V liq P vap independent of V gas P vap dependent on T Vapor Pressure 1 atm = 101325 Pa = 760 mm Hg = 760 Torr Depends on T: more thermal energy, more molecules can escape! Æ vapor pressure increases with T.
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Container open to atmosphere: When vapor pressure equals 1 atm: Boiling occurs Æ B.P. (pressure exerted by gas molecules = atmospheric pressure) Æ bubbles of vapor form throughout liquid Boiling Point At low pressure liquid boils at lower temperature At 1 atm liquids boil at T b ( normal boiling point ) Water: 100°C liquid vapor
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Vapor Pressure Curves (e) (d) (c) (b) (a) ln P = A ( ) + B 1 T A = H vap R ln = ( ) P 2 P 1 1 T 2 1 T 1 H vap R Clausius-Clapeyron Equation: Aniline C 6 H 7 N Toluene C 7 H 8 Water H 2 O Benzene C 6 H 6 Diethyl ether C 4 H 10 O
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Example 12B – Vapor Pressure of Water Find the vapor pressure of water at room temperature given H ° vap =44 kJ/mol.
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