lecture 4 - Why should soap make a floating paperclip sink?...

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Unformatted text preview: Why should soap make a floating paperclip sink? A. The soap is heavier than water. p B. The soap + water solution has a different surface tension than water. C. Adding soap influences the intermolecular forces. D. Adding soap coats the paperclip with soap. ... 1 Which f h following Whi h of the f ll i are true? ? A. A Evaporation is exothermic exothermic. B. Condensation is exothermic. C. C More molecules have enough energy to escape the intermolecular forces that hold them in a liquid at higher temperatures. q g p D. Energy is required to evaporate substances that interact through dipole-dipole g p p interactions. ... 2 Liquids--Distribution of Energies ... 3 Liquids--Evaporation To evaporate, molecules must have sufficient energy to break IM forces. t b k f Breaking IM forces requires energy. The q gy process of evaporation is endothermic. d th i ... 4 Liquids q HEAT OF VAPORIZATION is the heat needed (at constant P) to vaporize the liquid. Liquid + heat ---> Vapor q p Compound H 2O SO2 Xe Hvap (kJ/mol) ap IM Force ... 5 Example: How much energy (heat) is required to vaporize 1L of H2O? What do you need to solve this problem? ... UMass Amherst Biochemistry Teaching Initiative Liquids q Molecules in the vapor p state exert a VAPOR PRESSURE EQUILIBRIUM VAPOR PRESSURE is the pressure exerted by a t db vapor over a liquid in a closed container when the rate of evaporation = the rate of condensation. ... 7 Measuring Equilibrium Vapor Pressure Liquid in flask evaporates and exerts pressure on manometer. ... 8 Equilibrium Vapor Pressure ... 9 Equilibrium V E ilib i Vapor P Pressure 1. 1 The curves show all conditions of P and T where liquid and vapor are in EQUILIBRIUM 2. The VP rises with T. 3. 3 When VP = external P the liquid boils P, boils. This means that BP's of liquids change with altitude. ... 10 Equilibrium Vapor Pressure 4. If external P = 760 mm Hg, T of boiling is the NORMAL BOILING POINT 5. VP of a given molecule at a given T depends on IM forces. Here the VP's are in the order ether O C2H 5 H 5C2 dipoledipole dipole alcohol O H 5C2 H H-bonds water O H H extensive t i H-bonds increasing strength of IM interactions i i t th f i t ti ... 11 Equilibrium Vapor Pressure: The Clausius-Clapeyron Equation Clausius Clapeyron ClausiusClausius-Clapeyron equation is p y q used to find Hvap. H The logarithm of the vapor pressure P is proportional to Hvaporiation and to 1/T. ln P = (Hvap/RT) + C (H Hvap 1 P2 1 ln = T - T P1 R 1 2 ... 12 The Origin of Clausius-Clapeyron Equation ln P = (Hvap/RT) + C (H (H H ... 13 Example of Clausius-Clapeyron Equation in use: The vapor p p pressure of C4H10 is measured at different temperatures. What is the standard enthalpy of vaporization? ... 14 ...
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This note was uploaded on 04/15/2008 for the course CHEM 112 taught by Professor Hardy during the Spring '08 term at UMass (Amherst).

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