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BEHAVIOR OF GASES Chapter 14

BEHAVIOR OF GASES Chapter 14. 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(s) ---> 2 Na (s) + 3 N 2(g). THREE STATES OF MATTER. Click picture above to view movie on states of matter

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BEHAVIOR OF GASES Chapter 14

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  1. BEHAVIOR OF GASESChapter 14

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

  3. THREESTATES OF MATTER Click picture above to view movie on states of matter Click here for water production

  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 Theory Revisited 1. Gases consist of hard, spherical particles (usually molecules or atoms) 2. Small- so the individual volume is considered to be insignificant 3. Large empty space between them 4. Easily compressed and expanded 5. No attractive or repulsive forces 6. Move rapidly in constant motion

  6. Kinetic Theory Revisited • Recall: that the average kineticenergy of a collection of gas particles is directly proportional to the Kelvin temperature of the gas. • Click for movie • No Kinetic energy lost during collisions. • All particles have same energy at same temperature.

  7. 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 or kilopascal)

  8. Pressure Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643) Barometer calibrated for column width and pool width/depth

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

  10. Pressure Column height measures Pressure of atmosphere 1 standard atm = 760 mm Hg = 76 cm Hg = 760 torr = 29.9 inches = about 33 feet of water SI unit is PASCAL, Pa, where 1 atm = 101.325 kPa

  11. Gas -Volume, Temp, & Pressure • Click to view movie

  12. 1. Amount of Gas • When we inflate a ball, we are adding gas molecules. • Increasing the number of gas particles increases the number of collisions • thus, the pressure increases • If temp. is constant- doubling the number of particles doubles pressure

  13. Pressure and the Number of Molecules are Directly Related • Fewer molecules means fewer collisions. • Gases naturally move from areas of high pressure to low pressure because there is empty space to move in - spray can is example.

  14. Expanding Gas Uses? The bombardier beetle uses decomposition of hydrogen peroxide to defend itself. The gas acts as a propellant.

  15. The Shuttle Uses a Solid Booster and Uncontrolled Expanding Gases Can Be Disastrous

  16. If you double the number of molecules 1 atm

  17. If you double the number of molecules • You double the pressure. 2 atm

  18. 4 atm • As you remove molecules from a container

  19. 2 atm • As you remove molecules from a container the pressure decreases

  20. 1 atm • As you remove molecules from a container the pressure decreases • Until the pressure inside equals the pressure outside • Molecules naturally move from high to low pressure

  21. Changing the Size of the Container • In a smaller container molecules have less room to move. • Hit the sides of the container more often. • As volume decreases pressure increases. Think air pump

  22. 1 atm • As the pressure on a gas increases 4 Liters

  23. As the pressure on a gas increases the volume decreases • Pressure and volume are inversely related 2 atm 2 Liters

  24. What happens to the air in a diver’s lungs the deeper they go?

  25. Temperature • Raising the temperature of a gas increases the pressure if the volume is held constant. • The molecules hit the walls harder. • The only way to increase the temperature at constant pressure is to increase the volume.

  26. 300 K • If you start with 1 liter of gas at 1 atm pressure and 300 K • and heat it to 600 K one of 2 things happens

  27. 600 K 300 K • Either the volume will increase to 2 liters at 1 atm

  28. 600 K 300 K • Or the pressure will increase to 2 atm. • Or someplace in between

  29. The Gas Laws • Describe HOW gases behave. • Can be predicted by theory. • Amount of change can be calculated with mathematical equations.

  30. P V A. Boyle’s Law PV = k

  31. P V A. Boyle’s Law • The pressure and volume of a gas are inversely related • at constant mass & temp PV = k

  32. A. Boyle’s Law Click to view movie

  33. Boyle’s Law • At a constant temperature pressure and volume are inversely related. • As one goes up the other goes down • P x V = K (K is some constant) • Easier to use P1 x V1=P2 x V2 • Click for movie

  34. Boyle’s Gas Law Problems • A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa. BOYLE’S LAW GIVEN: V1 = 100. mL P1 = 150. kPa V2 = ? P2 = 200. kPa P V WORK: P1V1 = P2V2 (150.kPa)(100.mL)=(200.kPa)V2 V2 = 75.0 mL

  35. Examples • A balloon is filled with 25 L of air at 1.0 atm pressure. If the pressure is change to 1.5 atm what is the new volume? • A balloon is filled with 73 L of air at 1.3 atm pressure. What pressure is needed to change to volume to 43 L?

  36. V T B. Charles’ Law

  37. V T B. Charles’ Law • The volume and absolute temperature (K) of a gas are directly related • at constant mass & pressure

  38. Charles’ Law

  39. B. Charles’ Law Click for movie

  40. B. Charles’ Law • The volume of a gas is directly proportional to the Kelvin temperature if the pressure is held constant. • V = K xT (K is some constant) • V/T= K • V1/T1= V2/T2

  41. Gas Law Problems • A gas occupies 473 cm3 at 36°C. Find its volume at 94°C. CHARLES’ LAW GIVEN: V1 = 473 cm3 T1 = 36°C = 309K V2 = ? T2 = 94°C = 367K T V WORK: V1T2 = V2T1 (473 cm3)(367 K)=V2(309 K) V2 = 562 cm3

  42. Examples • What is the temperature (ºC) of a gas that is expanded from 2.5 L at 25ºC to 4.1L at constant pressure. • What is the final volume of a gas that starts at 8.3 L and 17ºC and is heated to 96ºC?

  43. P T C. Gay-Lussac’s Law

  44. P T C. Gay-Lussac’s Law • The pressure and absolute temperature (K) of a gas are directly related • at constant mass & volume

  45. C. Gay-Lussac’s Law • The temperature and the pressure of a gas are directly related at constant volume. • P = K xT (K is some constant) • P/T= K • P1/T1= P2/T2

  46. E. Gas Law Problems • A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr? GAY-LUSSAC’S LAW GIVEN: P1 = 765 torr T1 = 23°C = 296K P2 = 560. torr T2 = ? P T WORK: P1T2 = P2T1 (765 torr)T2 = (560. torr)(296K) T2 = 217 K = -56°C

  47. Examples • What is the pressure inside a 0.250 L can of deodorant that starts at 25ºC and 1.2 atm if the temperature is raised to 100ºC? • At what temperature will the can above have a pressure of 2.2 atm?

  48. Too Much Pressure and Not Enough Volume!!!!

  49. Putting the pieces together • The Combined Gas Law Deals with the situation where only the number of molecules stays constant. • (P1 x V1)/T1= (P2 x V2)/T2 • Allows us to figure out one thing when two of the others change.

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