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Air Pressure, Vapor Pressure, & Boiling

Air Pressure, Vapor Pressure, & Boiling. What is Air Pressure?. It is the Force of all the air molecules around an object pushing on that object. More air molecules equals more air pressure. What is Vapor Pressure?. It is the Force of the escaping Liquid molecules during vaporization.

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Air Pressure, Vapor Pressure, & Boiling

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  1. Air Pressure, Vapor Pressure, & Boiling

  2. What is Air Pressure? • It is the Force of all the air molecules around an object pushing on that object. • More air molecules equals more air pressure

  3. What is Vapor Pressure? • It is the Force of the escaping Liquid molecules during vaporization. • More Vaporization equals more vapor pressure. • During Evaporation - Low VP • During Boiling - High VP

  4. 10 mm of Hg Measuring Air Pressure • Air pressure is measured by using a Barometer. • It is measured in mm of Hg (Hg = Mercury)

  5. In order to make any liquid boil... • The Air pressure must equal the Vapor pressure.

  6. 713 742 760 785 How to Change AP • AP Decreases as altitude Increases. Denver Sea Level Pittsburgh Death Valley

  7. How to Change VP • VP Increases with an Increase in temperature. (The molecules are moving faster and a have a better chance of escaping)

  8. What are the 2 ways to make a liquid boil? • Lower the ____________ to the _______________ Air Pressure Vapor Pressure OR • Raise the ______________ to the _______________ Vapor Pressure Air Pressure

  9. What happens to VP with a Decrease in altitude? • Nothing happens to VP when you change Altitude. Remember that only the temperature affects the VP

  10. What happens to AP with an increase in altitude? • The AP will decrease as altitude increases.

  11. Is the water Boiling? • Water Temperature = 99.0 0C • Atmospheric Pressure (AP) = 733 mm of Hg • Yes the water would be boiling. • At 990C the VP = 733 mm of Hg • The VP does equals the AP

  12. What’s the VP? • Water is boiling at a temperature of 93.5 oC • About 600 mm of Hg (Using the graph)

  13. What’s the AP? • Water is boiling at 88.5oC • About 500 mm of Hg

  14. What’s the VP & AP • Water is boiling at 96.5 oC • The VP is About 670 mm of Hg • The AP is the same as VP since the water is boiling: About 670 mm of Hg

  15. What’s the Altitude? • The boiling point of water Decreases 1 oC for every 1000 ft Increase in altitude above sea level. • Water is Boiling at 96.5 oC

  16. How to Solve Altitude problems • Step 1: Normal Boiling point – Actual Boiling Point • Step 2: Multiply with the Conversion Factor • Step 3: Add the answer from #2 to Sea Level Altitude (0 ft) 100 C – 96.5 C = 3.5 C 1000 ft 3.5 C = 3500 ft X 1 C 3500 ft + 0 ft = 3500 ft

  17. How to Solve Altitude Problems –Part 2 • Do the steps in reverse: • Step 1: Subtract your Current Altitude from Normal Altitude (Sea Level or 0 ft) • Step 2: Multiply by the Conversion Factor: • Step 3: Subtract the answer from #2 from the Normal Boiling Point:

  18. Question #9: • Water is boiling at 6000 Ft above sea level. What is the temperature of the water?

  19. How to Solve Altitude problems • Step 1: Actual Altitude - Normal Altitude • Step 2: Multiply with the Conversion Factor • Step 3: Normal Boiling point – Change in Temp. 6000 ft – 0 ft = 6000 ft 1 C 6000 ft X = 6 C 1000 ft 100 C – 6 C = 94 C

  20. Question #10 • The VP of boiling water is 720 mm of Hg • What is the Temperature of the water? • Using your graph it is close to 98.5 C • What is the AP? • Since the water is boiling the AP must = the VP of 720 mm of Hg • At What Altitude? • Using the temperature of 98.5 the Altitude is found to be 1,500 ft

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