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Gases

Gases. Chapter 11 CHM 130 GCC. 11.1 Properties of Gases. Gases have no shape: they take the shape of their container Gases can expand & compress: V increases and atoms get farther apart, V decreases and atoms get closer together Gases have low densities: air is about 0.001 g /mL

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Gases

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  1. Gases Chapter 11 CHM 130 GCC

  2. 11.1 Properties of Gases • Gases have no shape: they take the shape of their container • Gases can expand & compress: V increases and atoms get farther apart, V decreases and atoms get closer together • Gases have low densities:air is about 0.001 g /mL • Gases mix completely with other gases:air is a mix of many gases like N2 (78%), O2 (21%), CO2, and noble gases • Gases exert pressure:they hit the sides of their container (exert force)

  3. 11.2 Pressure Pressure increases if • Number of collisions increase (more hits) • Energy of collisions increase (harder hits) There is no pressure in a vacuum Atmospheric pressure • Force of air above us hitting us • What happens if you climb Mt. Everest? As you climb, there is less air above you so pressure lessens, the air up high is less dense

  4. Barometer 1.00 atm = 760 torr = 760 mm Hg=14.7 psi The pressure of the air at sea level pushes the mercury liquid up 760 mm high.

  5. P Conversions A diver’s tank is at 4400 psi. Convert to torr, atm, and mmHg. 4400 psi ( 1 atm / 14.7 psi) = 3.0 x 102 atm 4400 psi( 760 torr / 14.7 psi) = 230,000 torr 230,000 torr = 230,000 mmHg

  6. 11.3 What affects Pressure? Decreases Increases Increases Indirect Direct Direct • If V increases, P ______ • If T increases, P ______ • If # gas atoms increases, P _____ Direct or Indirect Relationship? • P and V • P and T • P and # atoms

  7. Gas Laws 11.4 Boyle’s Law: P1V1 = P2V2 V1 = V2 T1 T2 11.5 Charles’s Law: P1 = P2 T1 T2 11.6 Gay-Lussac’s Law: P1V1 = P2V2 T1 T2 11.7 Combined Gas Law: STP = standard temperature and pressure = 1 atm and 0°C

  8. Videos if time • Sulfur Hexafluoride gashttp://www.youtube.com/watch?v=u19QfJWI1oQ&feature=youtube_gdata_player • How Density affects your voicehttp://www.youtube.com/watch?v=d-XbjFn3aqE&feature=youtube_gdata_player • Boyle’s law and lungs http://www.youtube.com/watch?v=NB1aCBId6qA • Boyle’s law and diving http://www.youtube.com/watch?v=sRrniZ0anCE&feature=related

  9. Gas Law Calculations • T must be in Kelvin (oC + 273 = K) • V same units on both sides to cancel • P same units on both sides to cancel • Identify all variables as before (1) or after the change (2) • If P, V, or T stays the same or is not mentioned, it cancels out • Plug in and solve, keep track of units and sig figs

  10. A sample of carbon dioxide gas occupies 2.25 L at 758 torr. Find the final volume if the pressure is decreased to 698 torr. P1V1 = P2V2 V2 = P1V1 / P2 V2 = (758 torr)(2.25L) / (698 torr) V2 = 2.44 L A sample of krypton gas occupies 3.91 L at 105oC. Find the temperature in oC of the gas if the volume is changed to 6.05 L. T2 = (6.05 L)(378 K) / 3.91 L T2 = 585 K and 585-273 = 312oC V1/T1 = V2/T2 T2 = V2T1 / V1

  11. A steel container filled with nitrous oxide at 15.0 atm is cooled from 25.5°C to –40.8°C. Calculate the final pressure. P2 = (15.0 atm)(232.2 K) / (298.5 K) P2 = 11.7 atm P1/T1 = P2/T2 P2 = P1T2 / T1 A nitrogen gas sample occupies 50.5 mL at –82.8°C and 1250 torr. What is the volume at STP? V2 = V2 = 119 mL P1V1/T1 = P2V2/T2 V2 = P1V1T2 / T1P2

  12. Dalton’s Law & Respiration (for fun) • Total P = sum of partial P • Ptot = P1 + P2 + P3 etc. • O2 is 21% of air by volume, so 21% of air P is due to O2 which is about 160 torr. • When blood exposed to air in lungs, the oxygen diffuses into the blood until the partial pressure in the liquid equals that of the gas in air • Gases move from a region of higher partial pressure to lower partial pressure • Partial pressure of O2 in pulmonary blood only about 40mmHg, compared to 104mmHg in alveoli. Diffusion occurs rapidly. • Partial P defined http://www.youtube.com/watch?v=tTGehRESHmA&feature=related • Diffusion http://www.youtube.com/watch?v=BatxnX5tXE0&feature=autoplay&list=PLB02A0A4A48238E7F&index • CO2 transport http://www.youtube.com/watch?v=x26TWL3VKMg&feature=mr_meh&list=PLB02A0A4A48238E7F&index=19&playnext=0

  13. Self Test • Page 320 • Try 1-7, 12-13, 15-16 • Answers in Appendix J

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