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BEHAVIOR OF GASES Chapter 12

BEHAVIOR OF GASES Chapter 12. THREE STATES OF MATTER. Importance of Gases. Airbags fill with N 2 gas in an accident. Gas is generated by the decomposition of sodium azide, NaN 3 . 2 NaN 3 ---> 2 Na + 3 N 2. General Properties of Gases. There is a lot of “free” space in a gas.

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BEHAVIOR OF GASES Chapter 12

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  1. BEHAVIOR OF GASESChapter 12

  2. THREE STATES OF MATTER

  3. Importance of Gases • Airbags fill with N2 gas in an accident. • Gas is generated by the decomposition of sodium azide, NaN3. • 2 NaN3 ---> 2 Na + 3 N2

  4. General Properties of Gases • There is a lot of “free” space in a gas. • Gases can be expanded infinitely. • Gases occupy containers uniformly and completely. • Gases diffuse and mix rapidly.

  5. KINETIC MOLECULAR THEORY(KMT) Theory used to explain gas laws • Gases consist of molecules in constant, random motion. • P arises from collisions with container walls. • Collisions elastic. No attractive / repulsive forces between molecules. • Volume of molecules is negligible.

  6. Properties of Gases Gas properties can be modeled using math. Model depends on— • V = volume of the gas (L) • T = temperature (K) • n = amount (moles) • P = pressure (atm)

  7. Pressure Air Pressure is measured with a BAROMETER (developed by Torricelli in 1643)

  8. Pressure Hg rises in tube until force of Hg (down) balances the force of air (pushing up). P of Hg pushing down related to • Hg density • column height

  9. Pressure Column height measures P 1 atm= 760 mm Hg or 29.9 inches Hg = 34 feet of water SI unit is PASCAL, Pa, 1 atm = 101.3 kPa

  10. twice as many molecules Avogadro’s Hypothesis Equalvolumes of gases at the same T and P have the samenumber of molecules. V = n (RT/P) = n k V and n are directly related.

  11. Avogadro’s Hypothesis and Standard Molar Volume V = n k = n x 22.4 L/mol at STP 1 mol of ANY gas occupies 22.4 L at STP + + = ? L 1mol 1mol 1mol

  12. Boyle’s Law If n and T are constant, then PV = (nRT) = k This means, P and V are inversely related Robert Boyle (1627-1691). Son of Early of Cork, Ireland.

  13. BOYLE’S LAB P inversely proportional to V

  14. Practice Problem • If you had a gas that exerted 202 kPa of pressure and took up a space of 3.00 liters. If you decide to expand the tank to 7.00 liters, what would be the new pressure? (Assume constant T) • P1V1=P2V2 • 202 kPa x 3.00 liters = P2 x 7.00 liters • 606 = P2 x 7.00 liters • P2 = 86.8 kPa

  15. Charles’s Law If n and P are constant, then V = (nR/P)T = kT V and T are directly related. Jacques Charles (1746-1823). Isolated boron and studied gases. Balloonist.

  16. Charles’s original balloon Modern long-distance balloon

  17. V is directly proportional to T

  18. Practice Problem • If you took a balloon outside 5.00C that was originally inside at 20.00C at 2.0 liters, what volume would the balloon occupy when cold? (constant P)

  19. Gas Volume, Temperature, and Pressure COMBINED GAS LAW: Combines Charles and Boyle’s Law P1V1 = P2V2 T1 T2

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