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Chapter 13: Gases

Chapter 13: Gases. What Are Gases?. Gases have mass. Properties of Gases. Easy to compress. What Are Gases?. Fill their containers completely. What Are Gases?. Move very quickly Movement of gases is called diffusion. What Are Gases?. Gases exert pressure Pressure is due to collisions.

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Chapter 13: Gases

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  1. Chapter 13:Gases

  2. What Are Gases? • Gases have mass

  3. Properties of Gases • Easy to compress

  4. What Are Gases? • Fill their containers completely

  5. What Are Gases? • Move very quickly • Movement of gases is called diffusion

  6. What Are Gases? • Gases exert pressure • Pressure is due to collisions

  7. Describing Behavior of Gases • Depends upon 4 variables • Amount of Gas (n) – Measured in Moles (mol) • Volume (V) – Measure in Liters (L) • Temperature (T) – Measured in Kelvin (K) • Pressure (P) – Measured in Pascals (Pa)

  8. Pressure • Pressure is the amount of force per given area • One newton of force per square meter is the Pascal • Often measure in kPa • 1013.25 millibars (mb) = 101.325 kPa = 1 atmosphere (atm) = 14.7 pounds per in2 (psi) = 760 mm of Hg (torr)

  9. Atmospheric Pressure • Pressure exerted by the atmosphere

  10. Atmospheric Pressure • Air Pressure measured by a barometer • Measured in mmHg

  11. Practice • High Pressure 1085 mb in Mongolia (2001) Convert to kPa • Low Pressure 870 mb in a Pacific Typhoon (1979) Convert to Atm

  12. Kinetic Molecular Theory • The behavior of gas is explained by the K–M theory of matter • Gases consist of particles that have mass 2. There are large distances between gas particles 3. Gas particles are in constant random motion

  13. Kinetic Molecular Theory 4. Collisions of gas particles with other particles or with the walls of the container are completely elastic. Elastic collision

  14. Kinetic Molecular Theory 5. Kinetic energy of gas depends upon temperature • High temperature, high KE 6. Gas particles exert no attractive forces between one another www.falstad.com/gas/

  15. Boyle’s Law • The pressure and volume of a sample of gas are inversely proportional at constant temperature • “spring of air” • P1V1=P2V2

  16. Charles’s Law • At constant pressure, the volume of a fixed amount of gas is directly proportional to its temperature. • Helped determine absolute zero • V1/T1=V2/T2 • All temperatures must be converted to Kelvin

  17. Practice • A weather balloon contains 150. L of gas, internal gas pressure is 1.0 atm. Atmospheric pressure at 41 km is 0.4 atm. Calculate the new volume of the balloon. • A sample of gas has a volume of 1 L at -18 0C. What is the temperature if the volume of the same gas is changed to 0.45 Liters?

  18. Practice • What will be the volume of a gas sample at 355 K if its volume at 273 K is 8.57 Liters? • 2.00 L of a gas is at 740.0 mmHg pressure. What is its volume at standard pressure?

  19. Dalton’s Law • Dalton’s Law of Partial Pressure states that the sum of the partial pressures of all of the components in a gas mixture is equal to the total pressure of the gas mixture. • PT = Pa + Pb + Pc ….

  20. Combined Gas Law • We can take all of the pressure-volume-temperature relationships we’ve just talked about and combine them into one gas law: (P1V1)/T1 = (P2V2)/T2 • If you remember this gas law, you can figure out the others.

  21. Practice • What is atmospheric pressure if the partial pressures of N2, O2, and Ar are 604.5 mm Hg, 162.8 mm Hg, and 0.5 mm Hg respectively? • If I have 21 liters of gas held at a pressure of 78 atm and a temperature of 900. K, what will be the volume of the gas if I decrease the pressure to 45 atm and decrease the temperature to 750 K?

  22. Ideal Gas Law • The ideal gas law combines all variables involved in a gas. PV = nRT • R is a constant • R = 0.0821 atm-L/mol-K • Temp must be in K • Pressure must be in Atm • Volume must be in Liters

  23. Ideal Gas vs. Real Gas • An Ideal Gas represents a gas as described by the kinetic-molecular theory. • Assumes no interaction between gas molecules • All gases are Real Gas • An ideal gas behaves >95% like a real gas. • Real Gases deviate from ideal gases at low temperatures and high pressures.

  24. Practice • How many moles of a gas at 100. oC does it take to fill a 1.00 Liter flask to a pressure of 1.50 atm? • What is the volume occupied by 9.45 g of C2H2 at STP?

  25. Atmospheric Pressure • Air pressure changes with altitude

  26. Atmospheric Pressure • Air pressure changes due to the heating by the sun

  27. Manometer • Enclosed gases may be measured by a manometer • Pressure of gas = height + air pressure

  28. Guy Lussac’s Law • At constant volume, the pressure of a fixed amount of gas is directly proportional to its temperature. • P1/T1=P2/T2 • All temperatures must be converted to Kelvin • Autoclaves

  29. Practice • You fill your car tires to 35 psi in the summer when it’s 31 °C. At Thanksgiving, when it’s -7 °C, you notice that your tire is low. What is the pressure inside your tires?

  30. Avogadro's Law • Avogadro’s Law states equal volumes of gases at the same temperature and pressure contain an equal number of particles. • Volume and amount are directly proportional. • V1/n1 = V2/n2

  31. Practice • The gases of carbon dioxide, oxygen, nitrogen, neon, and krypton are mixed in a container. All gases have the same partial pressure and the total pressure is 33,500 Pa. What is the partial pressure of nitrogen?

  32. Practice • I have an unknown volume of gas at a pressure of 0.5 atm and a temperature of 325 K. If I raise the pressure to 1.2 atm, decrease the temperature to 320 K, and measure the final volume to be 48 liters, what was the initial volume of the gas? • If I have 21 liters of gas held at a pressure of 78 atm and a temperature of 900 K, what will be the volume of the gas if I decrease the pressure to 45 atm and decrease the temperature to 750 K?

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