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Properties of Gases

Properties of Gases. Expand to completely fill their container Take the shape of their container Low density Much less than solid or liquid state Compressible Mixtures of gases are always homogeneous Fluid. Gas Laws – Kinetic Molecular Theory.

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Properties of Gases

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  1. Properties of Gases • Expand to completely fill their container • Take the shape of their container • Low density • Much less than solid or liquid state • Compressible • Mixtures of gases are always homogeneous • Fluid Chapter 6

  2. Gas Laws – Kinetic Molecular Theory • All matter is composed of tiny discrete particles called molecules • Molecules in a gas are in rapid constant motion and move in straight lines • Molecules of a gas are tiny compared with distances between gas molecules • There is little attraction between molecules of a gas Chapter 6

  3. Molecules collide with each other, with energy being conserved in the collision • Temperature (T) is a measure of the average kinetic energy of the gas molecules Chapter 6

  4. Pressure and Temperature (cont.) Chapter 6

  5. Volume Relationships • Law of combining volumes – when all measurements are made at same temperature and pressure, volumes of gaseous reactants and products are in small whole-number ratio Chapter 6

  6. Avogadro’s hypothesis – equal volumes of gases at constant pressure and temperature have the same number of molecules Chapter 6

  7. UNITS • Pressure • Temperature Chapter 6

  8. Molar Volume • Volume occupied by 1 mol of gas • Standard temperature and pressure (STP) • 1 atm pressure and 0°C • 1 mole of gas has volume of 22.4 L Chapter 6

  9. Talk about Density • This is at STP Chapter 6

  10. Boyle’s Law • PV=PV Chapter 6

  11. Talk about Lungs Chapter 6

  12. EXAMPLE Boyle's Law: Pressure-Volume Relationships Exercise A gas is enclosed in a 10.2-L tank at 1208 mmHg. (The mmHg is a pressure unit; 760 mmHg = 1 atm.) Which of the following is a reasonable value for the pressure when the gas is transferred to a 30.0-L tank? 300 mmHg 400 mmHg 3,600 mmHg 12,000 mmHg A gas is enclosed in a cylinder fitted with a piston. The volume of the gas is 2.00 L at 0.524 atm. The piston is moved to increase the gas pressure to 5.15 atm. Which of the following is a reasonable value for the volume of the gas at the greater pressure? 0.20 L 0.40 L 1.00 L 16.0 L

  13. EXAMPLE Boyle’s Law: Pressure-Volume Relationships A cylinder of oxygen has a volume of 2.25 L. The pressure of the gas is 1470 pounds per square inch (psi) at 20 °C. What volume will the oxygen occupy at standard atmospheric pressure (14.7 psi) assuming no temperature change?

  14. Exercise 2 Exercise 3 A sample of air occupies 73.3 mL at 98.7 atm and 0 ºC. What volume will the air occupy at 4.02 atm and 0 ºC? A sample of helium occupies 535 mL at 988 mmHg and 25 °C. If the sample is transferred to a 1.05-L flask at 25 °C, what will be the gas pressure in the flask? EXAMPLE Boyle’s Law: Pressure-Volume Relationships continued Chapter 6

  15. Charles’s Law Chapter 6

  16. Charles' Law • V/T = V/T Chapter 6

  17. Charles’s Law: Temperature-Volume Relationships EXAMPLE 6.15 A balloon indoors, where the temperature is 27 °C, has a volume of 2.00 L. What would its volume be (a) in a hot room where the temperature is 47 °C, and (b) outdoors, where the temperature is –23 ºC? (Assume no change in pressure in either case.)

  18. Charles’s Law: Temperature-Volume Relationships continued EXAMPLE 6.15 Exercise 6.15A Exercise 6.15B A sample of oxygen gas occupies a volume of 2.10 L at 25 °C. What volume will this sample occupy at 150 °C? (Assume no change in pressure.) b. A sample of hydrogen occupies 692 L at 602 °C. If the pressure is held constant, what volume will the gas occupy after being cooled to 23 °C? At what Celsius temperature will the initial volume of oxygen in Exercise 6.15A occupy 0.750 L? (Assume no change in pressure.) Chapter 6

  19. Ideal Gas Law PV = nRT • P = pressure • V = volume • n = number of moles • R = gas constant = 0.0821 L atm/mol K • T = absolute temperature Chapter 6

  20. EXAMPLE 6.16 Ideal Gas Law Exercise 6.16A Determine (a) the pressure exerted by 0.0330 mol of oxygen in an 18.0-L container at 313 K, and (b) the volume occupied by 0.200 mol of nitrogen gas at 298 K and 0.980 atm. Use the ideal gas law to calculate (a) the volume occupied by 2.00 mol of nitrogen gas at 244 K and .9500 atm pressure, and (b) the pressure exerted by 0.500 mol of oxygen in a 15.0-L container at 303 K.

  21. EXAMPLE 6.16 Ideal Gas Law continued Exercise 6.16B Determine the volume of nitrogen gas produced from the decomposition of 130 g sodium azide (about the amount in a typical automobile airbag) at 25 °C and 1 atm. Chapter 6

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