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Aim: What is the relationship between vapor pressure and boiling point?

Aim: What is the relationship between vapor pressure and boiling point?. Do Now: Use your glossary to define: 1. Evaporation 2. Vaporization 3. Boiling Point 4. Vapor Pressure. Unit 8: Gases & Gas Laws. Why does water evaporate when left outside?.

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Aim: What is the relationship between vapor pressure and boiling point?

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  1. Aim:What is the relationship between vapor pressure and boiling point? Do Now:Use your glossary to define:1. Evaporation2. Vaporization3. Boiling Point4. Vapor Pressure Unit 8: Gases & Gas Laws

  2. Why does water evaporate when left outside?

  3. The escape of molecules from the surface of a liquid to the gaseous state. Evaporation

  4. Which particle has a greater Kinetic Energy?

  5. What can cause the rate of evaporation to increase?

  6. Rate of evaporation increases with increasing temperature

  7. How do IMF affect evaporation? WHAT DO YOU MEAN, “What are IMF?”?!!!!

  8. Intermolecular Forces of Attraction: A Review • Dipole-dipole forces: Interactions between polar molecules • The more polar the molecule, the stronger the attraction!

  9. Intermolecular Forces of Attraction: A Review Hydrogen bonds: • A very strong dipole-dipole force between H the lone pair electrons on O, F, or N. • The more hydrogen bonding that a molecule can do, the stronger this force is. •  Water has a MP of 00 C, while methanol has a MP of -980 C.

  10. Intermolecular Forces of Attraction: A Review Van der Waals’ forces: • Between nonpolar molecules from temporarily induced dipoles. • The bigger the molecules, the stronger the force (because, after all, there are more electrons to become unbalanced and interact with each other). •  Neon has a MP of -2490, while F2 has a MP of -2200 C and methane has a MP of -1830 C.

  11. Ranking of IMF (Strongest to Weakest)  1. Ionic and covalent bonds are intramolecular forces It takes a huge amount of energy to break these. Example: The BP of NaCl is 14130 C. • 2. Intermolecular Forces: • a) Hydrogen bonding • Example: The BP of water is 1000 C. • b) Dipole-dipole forces • Example: The BP of H2S is -59.60 C. • c)Van derwaals forces • Example: The BP of methane is -161.50 C.

  12. Why are IMF important? • The stronger the intermolecular force, the higher the melting and boiling points. The stronger the attractive forces are, the more energy is required to break the attracting particles free of one another, and so more heat must be added to reach the melting and boiling point of the substance.

  13. Comparing five substances, each representative of their attractive force type, here is some example data:

  14. To summarize…Evaporation occurs more rapidly with…. Weaker intermolecular forces Higher temperatures

  15. Check for UnderstandingVolatile substances What type of intermolecular attractions do volatile substances have? Volatile = readily vaporizes at low temperatures.

  16. What happens when you leave the cap off a half filled water bottle? Period 6 Do Now:

  17. Vapor Pressure The pressure exerted by a vapor that is in equilibrium with it’s liquid state at a given temperature

  18. Closed System In a closed system molecules will reach dynamic equilibrium (rate of evaporation and condensation are the same)

  19. Dynamic Equilibrium Condition where two opposing processes are going on simultaneously at the same rate. There is no net change. Liquid Vapor

  20. Low vapor pressure Volatile substances (like propane) High vapor pressure Strong Intermolecular Forces Weak Intermolecular Forces Water Evaporates rapidly Evaporates more slowly Sort these phrases into two columns.

  21. Volatile substances (rubbing alcohol) Weak Intermolecular Forces Evaporates quickly High vapor pressure Strong Intermolecular Forces Water Evaporates slowly Low vapor pressure Making Connections

  22. PRESSURE Pressure: Force exerted over an area. • The gases in the atmosphere exert pressure because of Earth’s gravity. • Pressure is measured in atmospheres (atm), kilopascals (kPa) or millimeters of mercury (mmHg). • CONVERSIONS: 1.000 atm = 101.3 kPa = 760.0 mmHg • TRY THIS: Convert 50 kPa into atm.

  23. ATMOSPHERIC PRESSURE Atmospheric Pressure: Force exerted on an object by the weight of tiny particles in the air. • At high altitude, atmospheric pressure is __________. • At low altitude, atmospheric pressure is __________.

  24. The Effect of Atmospheric Pressure on Gas Particles • In terms of molecular behavior, what happens to the liquid water inside the can as it is heated on the hot plate? • What happens to vapor pressure? • What happens when the water vapor in the can is cooled by placing it into ice water? • What happens to vapor pressure during this phase change?

  25. Boiling Point • When vapor pressure equals atmospheric pressure, this is the boiling point of a substance. • Boiling point increases as pressure is increased. • Use Reference Table H to determine a liquid’s boiling point.

  26. High Altitude Low Atmospheric Pressure • Does it take more or less energy to boil water? • Is the boiling point higher or lower?

  27. Low Altitude High Atmospheric Pressure • Does it take more or less energy to boil water? • Is the boiling point higher or lower?

  28. Reading Table H Notice that the scales for the X and Y axis are different. Each box on the Y axis is 10 kPa, but every box on the X axis is 5oC.

  29. How To Use Table H: A) What is the vapor pressure of _____ at ____ oC? What is the vapor pressure of ethanol at 40oC? • Start at the 40oC point on the X axis, trace a line up to the ethanol curve, then shoot across and read the vapor pressure off of the Y axis. • The vapor pressure is __________.

  30. B) What is the boiling point of ______ at a pressure of ______ kPa? What is the boiling point of water at a pressure of 30 kPa? • Start at the 30 kPa point on the Y axis, trace a line to the water curve, then shoot down and read the temperature off the X axis. • The boiling point is 70oC.

  31. C) What is the normal boiling point of _____ ? The normal boiling point is the temperature at which a liquid boils under standard pressure, 101.3 kPa. • There is a dashed line going across the table at 101.3 and even labeled “101.3 kPa”. • Follow the 101.3 kPa line to the curve of your interest (in this case, water), and shoot down to get the boiling point from the X axis. • As expected, water has a normal boiling point of 100oC!

  32. Why does water evaporate at a slower rate than nail polish remover?

  33. How will an increase in temperature affect the vapor pressure? Would volatile substances have higher or lower vapor pressures at a given temperature? Why? What factors affect the rate of evaporation? What happens when evaporation occurs in a closed system? What is vapor pressure? How do intermolecular forces and temperature affect the pressure? Nearpod Recap

  34. HW: Vapor Pressure WS

  35. HW: Vapor Pressure WS

  36. HW: Vapor Pressure WS

  37. HW: Vapor Pressure WS

  38. HW: Vapor Pressure WS

  39. iPad Assignment due on Tuesday.

  40. Vapor Pressure - The pressure of the vapor resulting from evaporation of a liquid (or solid) above a sample of the liquid (or solid) in a closed container. • As the temperature of a liquid or solid increases its vapor pressure also increases. • Vapor pressure decreases as the temperature decreases. • The greater the rate of evaporation, the greater the vapor pressure.

  41. Vapor Pressure Equilibrium • When a solid or a liquid evaporates to a gas in a closed container, the molecules cannot escape. • Some of the gas molecules will eventually strike the condensed phase and condense back into it. • When the rate of condensation of the gas becomes equal to the rate of evaporation of the liquid or solid, the amount of gas, liquid and/or solid no longer changes. • The gas in the container is in equilibrium with the liquid or solid.

  42. http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swfhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swf

  43. Check For Understanding How will an increase in temperature affect the vapor pressure? Would volatile substances have higher or lower vapor pressures at a given temperature? Why?

  44. Evaporation Analysis What factors affect the rate of evaporation? What happens when evaporation occurs in a closed system? What is vapor pressure? How do intermolecular forces and temperature affect the pressure?

  45. Pressure Cooker A pressure cooker is designed to maintain pressures of 3-4 atm. What affect does this have on the boiling point?

  46. Investigation Why did Emeril need to revise his recipes when he opened up a restaurant in Denver?

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