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Chapter 11: Gases

Chapter 11: Gases. Section 1: Gases and Pressure. Units of Pressure. Millimeters of Mercury (mm Hg) is the most common because mercury barometers are most often used. Average atmospheric pressure at sea level at 0 ° C is 760 mm Hg .

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Chapter 11: Gases

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  1. Chapter 11:Gases

  2. Section 1: Gases and Pressure

  3. Units of Pressure • Millimeters of Mercury (mm Hg) is the most common because mercury barometers are most often used. Average atmospheric pressure at sea level at 0°C is 760 mm Hg. • Torr is another name for pressure when a mercury barometer is used in honor of Torricelli for his invention of the barometer. 1 torr = 1 mm Hg

  4. One atmosphere of pressure (1 atm) is defined as being exactly equivalent to 760 mm Hg. • One pascal (Pa) is defined as the pressure exerted by the force of one Newton (1 N) acting on an area of one square meter. Can also be expressed in kilopascals (kPa). 1 atm = 1.01325 x 105 Pa = 101.325 kPa 1 atm = 760 mm Hg = 760 torr

  5. Standard Temperature and Pressure • Because volumes of gases change so much when the temperature or pressure changes, scientists have agreed on standard conditions of exactly 1 atm pressure and 0˚C. • These are called standard temperature and pressure or STP.

  6. 738 mmHg 98.4 kPa

  7. Dalton’s Law of Partial Pressures • Partial Pressure is the pressure of each gas in a mixture of a gas. • Dalton’s Law of Partial Pressure states that the total pressure of a gas mixture is the sum of the partial pressures of the component gases. PT = P1 + P2 + P3 + … • PTis the total pressure of the mixture. • P1, P2, P3, and so on, are the partial pressures of the component gases.

  8. Example: • A container holds 3 gases: O2, CO2, and He. The partial pressure of the 3 gases are 2.00 atm, 3.00 atm, and 4.00 atm, respectively. What is the total pressure inside the container? • PT = 2.00 atm + 3.00 atm + 4.00 atm • PT = 9.00 atm

  9. Example: • A container with 2 gases, He and Ar, has a total pressure of 4.00 atm. If the partial pressure of He is 2.30 atm, what is the partial pressure of Ar? • 4.00 atm = 2.30 atm + PAr • PAr = 4.00-2.30 = 1.70 atm

  10. Gases Collected by Water Displacement • Gases produced in the lab are often collected over water, through a method known as water displacement. Water molecules mix with the gas molecules and the resulting water vapor experts its own pressure, known as vapor pressure. • The pressure of the water vapor must be taken into account when determining the pressure of the gas. Patm = Pgas + PH20 • The vapor pressure of water is dependent on temperature (Table A-8 on page 859).

  11. Example: • Oxygen gas from the decomposition of potassium chlorate, KClO3, was collected by water displacement. The barometric pressure and the temperature during the experiment were 731.0 torr and 20.0°C. What was the partial pressure of the oxygen collected? • Patm = 731.0 torr and PH2O = 17.5 torr at 20.0°C • Patm = PO2 + PH2O  PO2 = Patm – PH2O • PO2 = 731.0 torr – 17.5 torr = 713.5 torr

  12. Example: • Some Hydrogen gas is collected over water at 20.0°C. The partial pressure of hydrogen is 742.5 torr. What was the barometric pressure at the time the gas was collected? • PH2 = 742.5 torr and PH2O = 17.5 torr at 20.0°C • Patm = PH2 + PH2O • Patm = 742.5 torr + 17.5 torr = 760.0 torr

  13. Section 2:The Gas Laws

  14. Boyle’s Law: Pressure-Volume Relationship P1x V1 = P2 x V2 • What must stay constant for Boyle’s Law to work? Temperature • Pressure can be in any unit, but both must be the same. • Volume can be in any unit, but both must be the same.

  15. Example:

  16. Example: • A balloon filled with helium gas has a volume of 500 mL at a pressure of 1 atm. If the pressure decreases to 0.5 atm and the temperature remained the same, what volume does the gas now occupy? • Trying to find the new volume V2 • Plug in the 3 known values and solve. 1 atm x 500 mL = 0.5 atm x V2 V2 = 1000 mL

  17. Charles’s Law: Volume-Temperature Relationship

  18. Example:

  19. Gay-Lussac’s Law: Pressure-Temperature Relationship

  20. Example:

  21. Example:

  22. Example:

  23. The Combined Gas Law

  24. Example:

  25. Example:

  26. Section 3:Gas Volumes and Ideal Gas Law

  27. Standard Molar Volume of A Gas: the volume occupied by one mole of a gas at STP is 22.4 L. 22.4 L or 1 mol 1 mol 22.4 L • Using this conversion, you can get from grams  moles  Liters or vice versa. • Remember: this only works at STP

  28. Example 20.12 mmHg 0.987 mol

  29. Ideal Gas Law

  30. Example

  31. Section 4:Diffusion and Effusion

  32. Graham’s Law of Effusion

  33. Examples

  34. Examples

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