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Gases

Gases . Chapter 13. Pressure . What are the properties of gases? Occupies the volume of its container Mixes completely with any other gas Easily compressed Exerts a pressure on its surroundings. Kinetic Theory . Kinetic energy – energy of motion

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Gases

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  1. Gases Chapter 13

  2. Pressure • What are the properties of gases? • Occupies the volume of its container • Mixes completely with any other gas • Easily compressed • Exerts a pressure on its surroundings

  3. Kinetic Theory Kinetic energy – energy of motion Kinetic theory- all matter consists of tiny particles always in motion

  4. Assumptions of Kinetic Theory Gases are composed of tiny particles (atoms or molecules) So small that the actual volume of the particles is assumed to be zero Particles in constant random motion, colliding with the wall of the container-gas pressure Intermolecular attractions negligible Average kinetic energy of the particles is directly proportional to the Kelvin temperature of the gas

  5. 13.1 Kinetic Theory and a Model for Gases • Particles in a gas are in rapid, constant motion.

  6. Elastic collisions Elastic collisions – kinetic energy is transferred without loss from one particle to another, and the total kinetic energy remains constant

  7. Gas Pressure • Simultaneous collisions of billions of rapidly moving gas particles with an object • No particles and no pressure – vacuum • Atmospheric pressure- collisions of the atoms and molecules in air with objects • Why does atmospheric pressure decrease when you climb a mountain?

  8. Pressure The pressure is on us! Barometer – measures atmospheric pressure

  9. Units of Pressure mmHg (height of mercury in barometer) torr (named after Toricelli) atm (standard atmosphere) Pa (pascal the SI unit for pressure) 760 mmHg = 1 torr = 1 atm = 101.3 kPa

  10. Pressure Unit Conversions Ex. The height of mercury in a mercury barometer is measured to be 732 mm. Represent this pressure in atm, torr, and pascals.

  11. Manometer Used to measure the pressure of a gas in a container http://www.kentchemistry.com/links/Matter/VaporPressure.htm

  12. Boyle’s Law • Robert Boyle born in 1627 • Known for his works in mechanics, medicine, hydrodynamics and chemistry • Published The Spring and the Weight of the Air in 1662 which contained his pressure-volume inverse relationship

  13. Boyle’s Law: Pressure and Volume • Boyle’s law states that for a given mass of gas at constant temperature, the volume of the gas varies inversely with pressure.

  14. Practical Applications? Ear popping? Aerosol cans ? Hole in your pen?

  15. Boyle’s Law Problem A sample of helium gas has a pressure of 3.54 atm in a container with a volume of 23.1 L. This sample is transferred to a new container and the pressure is measured to be 1 atm, What is the volume of the new container? Assume constant temperature.

  16. Charles’ Law Jacques Alexander Cesar Charles Born in France in 1746 Chemist, physicist, aeronaut Formulated gas law in1787 which states that pressure and volume occupied by a fixed weight of gas is directly proportional to the absolute temperature

  17. Charles’s Law: Temperature and Volume • As the temperature of an enclosed gas increases, the volume increases, if the pressure is constant.

  18. Charles’s Law: Temperature and Volume • As the temperature of the water increases, the volume of the balloon increases.

  19. Charles’ Law: Temperature and Volume • Charles’s law states that the volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant.

  20. Gay-Lussac Law Joseph Gay-Lussac French experimental chemist Fixed amount of gas at fixed volume, pressure is proportional to temperature Published in 1801

  21. Gay-Lussac’s Law: Pressure and Temperature • As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant.

  22. Gay-Lussac’s Law: Pressure and Temperature • When a gas is heated at constant volume, the pressure increases.

  23. Gay-Lussac’s Law: Pressure and Temperature • Gay-Lussac’s law states that the pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant.

  24. Practical Applications • Bullets and cannons • Hurricanes

  25. Simulation • http://phet.colorado.edu/en/simulation/gas-properties • http://www.grc.nasa.gov/WWW/K-12/airplane/Animation/frglab2.html

  26. Combined Gas Law Derived by multiplying Charles’ Law, Boyle’s Law, and Gay Lussac’s Law (P1V1)=(P2V2) T1 T2

  27. Example A gas occupies a volume of 20L at a pressure of 5 atm and temperature of 500K. What will be the volume if both the pressure is raised to 10 atm and temperature changed to 250K?

  28. Avogadro’s Law For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles in a gas V1 = V1 n1 n1

  29. Ideal Gas Law • The gas law that includes all four variables—P, V, T, and n—is called the ideal gas law. • The ideal gas constant (R) has the value 8.31 (L·kPa)/(K·mol).

  30. 1. An aerosol spray can with a volume of 325 mL contains 3.00 g of propane (C3H8) as a propellant. What is the pressure in atm of the gas in the can at 28°C? • 524 kPa • 2.31 104kPa • 475 kPa • 0.524 kPa

  31. 2. Find the volume of a gas in liters if 2.95 mol has a pressure of 77.0 kPa at a temperature of 52°C. • 22.4 L • 16.6 L • 103 L • 50.2 L

  32. 3. An ideal gas differs from a real gas in that the molecules of an ideal gas • have no attraction for one another. • have a significant volume. • have a molar mass of zero. • have no kinetic energy.

  33. Dalton’s Law • The contribution each gas in a mixture makes to the total pressure is called the partial pressure exerted by that gas.

  34. Dalton’s Law • In a mixture of gases, the total pressure is the sum of the partial pressures of the gases.

  35. Dalton’s Law • Dalton’s law of partial pressures states that, at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases.

  36. Graham’s Law of Effusion What is the difference between effusion and diffusion?

  37. Graham’s Law • Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout.

  38. Graham’s Law • Bromine vapor is diffusing upward through the air in a graduated cylinder.

  39. Graham’s Law • After several hours, the bromine has diffused almost to the top of the cylinder.

  40. Graham’s Law • During effusion, a gas escapes through a tiny hole in its container. • Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.

  41. Diffusion vs Effusion

  42. Graham’s Law • Thomas Graham’s Contribution • Graham’slaw of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases.

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