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Learn about atmospheric pressure, barometers, units of pressure, and the relationships between pressure, volume, and temperature in gases. Practice calculations involving Boyle's Law, Charles's Law, Avogadro's Law, and Gay-Lussac's Law.

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  1. Chapter Preview: • How does a gas differ from a solid and a liquid • Have you heard of the term barometric pressure? What does it mean? • What does the temperature of a sample measure?

  2. Objectives • To learn about atmospheric pressure and how barometers work • To learn the units of pressure • To understand how the pressure and volume of a gas are related • To do calculations involving Boyle’s Law • To learn about absolute zero • To understand how the volume and temperature of a gas are related • To do calculations involving Charles’s Law • To understand how the volume and number of moles of a gas are related • To do calculations involving Avogadro’s Law

  3. A. Pressure Atmospheric Pressure • Changing weather conditions

  4. A. Pressure Atmospheric Pressure • Changing altitude

  5. A. Pressure Measuring Pressure • Barometer – device that measures atmospheric pressure • Invented by Evangelista Torricelli in 1643

  6. A. Pressure • Barometer

  7. A. Pressure Units of Pressure 1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr = 101,325 Pa = 14.70 psi (lb/in2) = 29.9 in. Hg = 1013 mbar

  8. Converting Pressure Units • On a summer day in Breckenridge, Colorado, the atmospheric pressure is 525 mm Hg. What is the air pressure in atmospheres (atm)? mm Hg and atm are related by the unit equality: 1.000 atm = 760.0 mm Hg Therefore: (525 mm Hg)(1.000 atm/760.0 mm Hg) = 0.691 atm

  9. Practice Problems • The height of mercury in a mercury barometer is measured to be 732 mm Hg. Calculate this pressure in atm. • The pressure of a gas is measured to be 2.79 x 105 Pa. Represent this pressure in mm Hg. 3. The air pressure in a submarine is 0.62 atm. What is the pressure in psi?

  10. A. Pressure Units of Pressure • A manometer measures the pressure of a gas in a container.

  11. Measuring Pressure • A balloon is attached to an open-ended manometer. The difference in height of the mercury column is 13 mm. The side attached to the balloon is lower than the side open to the atmosphere. If the pressure of the atmosphere is known to be 755 mm Hg, what is the gas pressure in the balloon? 2. A gas container is attached to a manometer. The level of the mercury is 15 mm lower on the open side. If the atmospheric pressure is 750 mm Hg, what is the pressure of the gas in the container?

  12. Pressure and Volume Class Warmup Describe what will happen to a sample of gas in a container if the container volume is doubled but the temperature and amount of gas stays the same.

  13. B. Pressure and Volume: Boyle’s Law • 1662 – Robert Boyle discovered the relationship between pressure and volume • The volume of a fixed amount of gas is inversely proportional to the pressure at constant temperature.

  14. B. Pressure and Volume: Boyle’s Law • As volume decreases, particles collide more often so the pressure increases. If volume increases, particles collide less frequently and pressure decreases.

  15. B. Pressure and Volume: Boyle’s Law PV = k Or P1V1=P2V2

  16. C. Volume and Temperature: Charles Law Class Warmup: Describe what will happen to a sample of a gas in a container that is free to expand or contract if the temperature of the gas is increased.

  17. C. Volume and Temperature: Charles Law • The relationship between volume and temperature of a gas was discovered by Jacques Charles in 1787. • The volume of a fixed mass of gas at constant pressure is directly proportional to the Kelvin temperature.

  18. C. Volume and Temperature: Charles’s Law Or….

  19. C. Volume and Temperature: Charles’s Law • Absolute zero – temperature at which a gas volume becomes zero (all particle motions stops • -273oC  0 Kelvin (K)

  20. D. Volume and Moles: Avogadro’s Law What happens when gas particles are added to a container that that is free to expand or contract. Assume the temperature is constant?

  21. D. Volume and Moles: Avogadro’s Law

  22. D. Volume and Moles: Avogadro’s Law • Volume and moles are directly proportional at constant temperature and pressure • If one increases the other increases.

  23. D. Volume and Moles: Avogadro’s Law • Discovered in 1811 by AmadeoAvodgadro • Equal volumes of a gas at constant temperature and pressure contain equal number of particles.

  24. D. Volume and Moles: Avogadro’s Law Practice Problems: • If 2.55 moles of helium gas occupies a volume of 59.5 L at a particular temperature and pressure, what volume does 7.83 moles of helium occupy under the same conditions? 2. If 4.35 g of neon gas occupies a volume of 15.0 L at a particular temperature and pressure, what volume does 2.00 g of neon gas occupy under the same conditions?

  25. Pressure and Temperature: Gay-Lussac’s Law Describe what happens to a sample of gas in a rigid sealed container if the gas is heated.

  26. E. Pressure and Temperature: Gay-Lussac’s Law • Pressure and Temperature are directly proportional -P and T are related by the equation: P/T = k (constant) - at constant volume and constant amount of gas • Another way of stating Gay-Lussac’s Law is: P1 = P2 T1 T2

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