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Chapter 10 Gases

Chemistry, The Central Science , 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten. Chapter 10 Gases. John Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc. Characteristics of Gases. Unlike liquids and solids, they

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Chapter 10 Gases

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  1. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chapter 10Gases John Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc.

  2. Characteristics of Gases • Unlike liquids and solids, they • Expand to fill their containers. • Are highly compressible. • Have extremely low densities. • What is compressible?

  3. F A P = Pressure • Pressure is the amount of force applied to an area. • Atmospheric pressure is the weight of air per unit of area.

  4. Units of Pressure • Pascals • Bar • Torr • Atmosphere (Atm)

  5. Standard Pressure • Normal atmospheric pressure at sea level. • It is equal to • 1.00 atm • 760 torr (760 mm Hg) • 101.325 kPa

  6. Boyle’s Law The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure.

  7. Boyle’s Law

  8. V T = k • i.e., Charles’s Law • The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature. A plot of V versus T will be a straight line.

  9. V = kn • Mathematically, this means Avogadro’s Law • The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas.

  10. Dalton’s Law ofPartial Pressures • The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone. • In other words, • Ptotal = P1 + P2 + P3 + …

  11. Kinetic-Molecular Theory This is a model that aids in our understanding of what happens to gas particles as environmental conditions change.

  12. Main Tenets of Kinetic-Molecular Theory Gases consist of large numbers of molecules that are in continuous, random motion.

  13. Main Tenets of Kinetic-Molecular Theory • The combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained. • Attractive and repulsive forces between gas molecules are negligible.

  14. Main Tenets of Kinetic-Molecular Theory Energy can be transferred between molecules during collisions, but the average kinetic energy of the molecules does not change with time, as long as the temperature of the gas remains constant.

  15. Effusion The escape of gas molecules through a tiny hole into an evacuated space.

  16. Diffusion The spread of one substance throughout a space or throughout a second substance.

  17. Real Gases In the real world, the behavior of gases only conforms to the ideal-gas equation at relatively high temperature and low pressure.

  18. Deviations from Ideal Behavior The assumptions made in the kinetic-molecular model break down at high pressure and/or low temperature.

  19. Review • Name the gas laws

  20. Review • How are gases unique

  21. Review • What is the difference between effusion and diffusion? • What is the difference between real and Ideal gas?

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