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VAPOR PRESSURE OF WATER

Experiment #2. VAPOR PRESSURE OF WATER. What are we doing in this experiment?. Determine the vapor pressure of water at different temperatures. . 2. Determine the heat of vaporization of water. Review of Gas laws. Boyle’s Law:. Charle’s Law:. Avogadros’s Law:. IDEAL GAS LAW.

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VAPOR PRESSURE OF WATER

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  1. Experiment #2 VAPOR PRESSURE OF WATER

  2. What are we doing in this experiment? • Determine the vapor pressure of water • at different temperatures. 2. Determine the heat of vaporization of water.

  3. Review of Gas laws Boyle’s Law: Charle’s Law: Avogadros’s Law: IDEAL GAS LAW

  4. IDEAL GAS LAW Units of P: atmospheres Units of V: Liters Units of T: kelvin Units of R:

  5. Dalton’s law of partial pressure A + B + C Ptotal= PA + PB + PC

  6. Relation between mole fraction and partial pressure of a gas A + B Ptotal= PA + PB

  7. What is VAPOR PRESSURE OF WATER? It is the pressure (technically, partial pressure) exerted by the water molecules in the vapor phase (gas, water vapor) above the surface of a liquid at equilibrium at that temperature. Pvap Vapor phase or Water vapor Liquid phase Heat

  8. Define Pressure It is defined as force applied per unit area Units of pressure:

  9. H H O--H-O-H - - O H H Why does water not vaporize by itself quickly? Atmosphere Vapor phase or Water vapor Liquid phase Strong inter molecular hydrogen bonds

  10. When does a liquid boil? Vapor pressure of the liquid = surrounding atmospheric pressure What is boiling point of a liquid ? It is the temperature at which, Vapor pressure of the liquid = surrounding atmospheric pressure Normal boiling point: If Patm= 1.0 atm

  11. Composition of Dry Air Gas % by volume N2 O2 Ar CO2 Rest 78.09 20.94 0.93 0.03 0.01

  12. What does it mean if a liquid has high vapor pressure? • More molecules are found in the • vapor phase. 2. Does not require a lot of energy to vaporize the liquid. 3. Weak inter molecular attractive forces holding the molecules together in their liquid state.

  13. A comparison Closed system Open system Heat Heat Rate of vaporization can equal rate of condensation Rate of vaporization cannot equal rate of condensation Dynamic equilibrium not reachable Dynamic equilibrium reachable

  14. A comparison Closed system Open system Heat Heat As the temperature is increased, We can send more and more molecules in to Vapor phase There can only be a fixed number of molecules that can be in the vapor phase

  15. A comparison Closed system Open system Heat Heat The maximum vapor pressure that can be reached here is atmoshpheric pressure The maximum vapor pressure that can be reached here is more than the atmoshpheric pressure

  16. What is VAPOR PRESSURE OF WATER? It is the pressure (technically, partial pressure) exerted by the water molecules in the vapor phase (gas, water vapor) above the surface of a liquid at equilibrium at that temperature. Pvap Vapor phase or Water vapor Liquid phase Heat

  17. EXPERIMENTAL SETUP Surface of water should cover test tube. Magnetic stir-bar (position carefully) Air bubble at the top of a inverted test tube Stirrer/hot plate

  18. 0 1 2 3 4 5 6 7 8 Paste the scale on a 100 mm test tube as shown, with the scale facing inside of the tube Cut the scale out from the manual Note: This scale is unit less and does not correspond to inches or centimeters.

  19. EXPERIMENTAL SETUP Surface of water should cover test tube. Magnetic stir-bar (position carefully) Air bubble at the top of a inverted test tube Stirrer/hot plate

  20. What are we going to do? • Measure the volume of the bubble at • different temperatures Charle’s Law Low temperature Higher temperature As temperature increase, the volume increases (at constant P,n)

  21. What are we going to do? 2. Calculate the pressure contribution from N2 and O2 in the bubble using the ideal gas equation. 3. Calculate the vapor pressure of water. Ptotal= PN2 + PO2+ Pwvap PN2 and PO2 are much greater than Pwvap Ptotal= PNO+ Pwvap But, Ptotal inside the bubble = Patmosphere So, we have Patmosphere= PNO+ Pwvap Pwvap= Patmosphere- PNO

  22. How to convert the change in the number of divisions to change in volume? Have to find out the relationship between the number of divisions to number of mL

  23. Vi Vo S=4.5 Burrette Filled with water VN Unscaled Volume, Vu=vo-vi

  24. DATA Please use 3 sig. figs., and scientific notation

  25. HEAT OF VAPORIZATION DEFINITION It is defined as the heat required to vaporize (converting a liquid to gas) one mole of a substance at constant pressure and temperature. The heat of vaporization is expressed in kJ/mol. ` vap

  26. HEAT OF VAPORIZATION Clausius-Clapeyron equation R=8.314 J/K mol

  27. intercept LnPwvap= m(1/T) + Z 1/Tk, (k-1) X1 x2 y Equation of the best-fit line: 1 x Y=mX + z Y1 LnPwvap (unitless) Best-fit line m = slope = 2 x Y2 x R=8.314 J/K mol

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