continuation of chapter 11 chem 1212. prentice hall © 2003chapter 11 vapor pressure vapor pressure...
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Continuation of CHAPTER 11
CHEM 1212
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Prentice Hall © 2003 Chapter 11
Vapor Pressure
• Vapor pressure is the pressure exerted when the liquid and vapor are in dynamic equilibrium.
• Dynamic Equilibrium - the point when as many molecules escape the surface as strike the surface.
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What you have learned so far…….
• Some compounds are volatile (evaporates easily) because… (a) the molecules are held together by weak intermolecular forces therefore it doesn’t take much E to break the bonds and so they evaporate easily.
• Compounds that are volatile have lower boiling points.
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Chapter 11
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Clausius-Clapeyron Equation
• ln P = - DHvap + C RT
Where:T = absolute temperatureR = gas constant (8.314 J/K-mol)DH = heat of vaporizationP = vapor pressureC = constant
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IDEAL GAS CONSTANT
• R = 0.08206 liter . atm/K . Mole• OR
• R = 8.314 J/K . mole
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Vapor Pressure and Boiling Pt.
• Sample Problem
• If the normal boiling point of water is 100. oC, what will be its boiling point at 735 torr? The heat of vaporization of water is 40.67 kJ/mole.
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Clausius-Clapeyron Equation
• To determine the effect of changing temperature or vapor pressure, use the following equation:
• ln [P1/P2] = - DHvap [1/T1 - 1/T2]
R
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Clausius-Clapeyron Equation
So your very first equation in Chem 1212 is:
• ln [P1/P2] = DHvap [1/T2 - 1/T1]
R
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Problem
CCl4 has a vapor pressure of 213 torr at 40 oC and 836 torr at 80 oC. What is the heat of vaporization of CCl4?
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Extra Problem
• The melting point of potassium is 63.2 oC. Molten potassium has a vapor pressure of 10.0 torr at 443 oC and a vapor pressure of 400.0 torr at 708 oC.
• A.) Calculate the heat of vaporization of liquid potassium.
• B.) Calculate the normal boiling point of potassium.
• C.) Calculate the vapor pressure of liquid potassium at 100 oC.