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Continuation of CHAPTER 11

Continuation of CHAPTER 11. CHEM 1212. 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. What you have learned so far…….

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Continuation of CHAPTER 11

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  1. Continuation of CHAPTER 11 CHEM 1212

  2. 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. Chapter 11

  3. 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. Chapter 11

  4. Chapter 11

  5. Clausius-Clapeyron Equation • ln P = - DHvap + C RT Where: T = absolute temperature R = gas constant (8.314 J/K-mol) DH = heat of vaporization P = vapor pressure C = constant Chapter 11

  6. 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. Chapter 11

  7. 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 Chapter 11

  8. Clausius-Clapeyron Equation So your very first equation in Chem 1212 is: • ln [P1/P2] = DHvap [1/T2 - 1/T1] R Chapter 11

  9. Problem CCl4 has a vapor pressure of 213 torr at 40 oC and 836 torr at 80 oC. What is the normal boiling point of CCl4? Chapter 11

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