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BEHAVIOR OF GASES

BEHAVIOR OF GASES. UNIT 12 CHAPTER 12. Kinetic Molecular Theory. Theory developed to help understand the nature and behavior of gases. The theory states… Gas are very far apart in comparison to their own size. This allows gases to be compressed (volume changes under pressure)

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BEHAVIOR OF GASES

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  1. BEHAVIOR OF GASES UNIT 12 CHAPTER 12

  2. Kinetic Molecular Theory • Theory developed to help understand the nature and behavior of gases. • The theory states… • Gas are very far apart in comparison to their own size. This allows gases to be compressed (volume changes under pressure) • NO attractive or repulsive forces exist between the particles allowing the particles to move easily and take the shape of its container. • Gas particles move in a constant, rapid, straight line (random motion) in a container making perfectly elastic collisions (no energy is lost) with the walls.

  3. NET MOVEMENT Diffusion vs. Effusion • diffusion: particle movement from high to low concentration • effusion: diffusion of gas particles through an opening

  4. Graham’s Law of Effusion • Smaller particles move (diffuse or effuse) faster than bigger particles. • Compare the molecular masses of the gases to determine which one moves faster.

  5. Ex. Compare the rates of diffusion of Krypton and Argon. Which gas would diffuse faster? • Ex. Compare the rates of diffusion for methane and ammonia. Which gas would diffuse faster?

  6. Variables that Describe Gases • Gas properties can be modeled using math. The models depend on the following variables… • (V): Volume of the gas. • Measured in Liters (L) • (T): Temperature of the gas. • MUST be in Kelvin (K) • (n): Amount of moles of the gas • Measured in um….moles! • (P): pressure of the gas • Measured in Atmospheres (atm)

  7. Volume • Avogadro hypothesized that if you had two containers that are the same temperature and pressure, then they would be able to hold the same amount of gas. • At standard temperature and pressure (STP), 1 mol = 22.4 L. This is a useful equations • Example: What is the volume of .202 mol of gas at STP?

  8. Pressure • Defined as the force per unit area which the gas molecules exert on the walls of their containers due to the collision of molecules. • Gases in the atmosphere exert a pressure on anything they come in contact with • The pressure on objects due to the air around them is called atmospheric pressure. • Standard pressure (at sea level): 1 atm = 101.3 KPa = 760 torr = 760 mmHg

  9. Temperature • Standard Temperature: temperature at which water freezes at standard pressure • 0°C = 273 K

  10. Boyle’s Law • Robert Boyle (1627-1691) • Pressure & Volume are inversely proportional to each other… • Pressure increases & volume decreases… • Pressure decreases & volume increases…. • P1V1 = P2V2 • Moles & temperature are constant

  11. Boyle’s Law http://www.grc.nasa.gov/WWW/K-12/airplane/aboyle.html

  12. Boyle’s Law • Examples: • Syringes • Balloons • Bicycle pumps

  13. Boyle’s Law:Applying the Math • P1V1 = P2V2 • A high altitude balloon contains 30.0 L of He gas at 103 kPa. What is the volume when the balloon rises to an altitude where the pressure is only 25.0 kPa? P1 = 103 kPa P2 = 25.0 kPa V1 = 30.0 L V2 = ??? (103)(30.0) = (25.0) V2 3090 = 25.0V2 123.6 = V2

  14. Charles’s Law • Jacques Charles (1746-1823) • Temperature and volume are directly proportional to each other… • If temperature increases, volume increases and vice versa… • V1 = V2 T1 T2 • Pressure and moles are constant

  15. Charles’s Law

  16. Charles’s Law • Examples: • Hot air balloons

  17. Charles’s Law:Applying the Math • V1 = V2 T1 T2 • A balloon is inflated in a room at 24 °C and has a volume of 4.00 L. The balloon is heated to a temperature of 58 °C. What is the new volume? V1 = 4.00L V2= ?? T1 = 297 KT2 = 331 K 4.00 = V2 297 331 1324 = 297V2 4.46 = V2

  18. Gay-Lussac’s Law • Joseph Louis Gay Lussac (1778-1850) • Pressure and temperature are directly proportional to each other… • If temperature increases, pressure will increase and vice versa… • P1 = P2 T1 T2 • Moles and volume are constants

  19. Gay-Lussac’s Law • http://preparatorychemistry.com/Bishop_Gay_Lussac_frames.htm • http://www.youtube.com/watch?v=Y4rurDe7s3c&feature=related • Example: • Autoclave: sterilizes medical equipment

  20. Gay-Lussac’s Law:Applying the Math • P1 = P2 T1 T2 • A gas is under pressure of 103 kPa at 25 °C. What would happen to the pressure if the temperature was raised to 298 °C? P1 = 103 kPa P2= ?? T1= 298 K T2 = 571 K 103 = P2 298 571 58813 = 298P2 197.3 kPa = P2

  21. Combined Gas Law • The good news is that you do NOT need to memorize each individual equation. Since they are all related to each other, we can combine them into a single equation. • KNOW THIS EQUATION!!!!! MEMORIZE IT! • P1 V1 = P2 V2 T1 T2

  22. Combined Gas Law If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law! = P2 Boyle’s Law Charles’ Law Gay-Lussac’s Law P1 V2 V1 T1 T2

  23. Combined Gas Law Problem A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm? Set up Data Table P1 = 0.800 atm V1 = 180 mL T1 = 302 K P2 = 3.20 atm V2= 90 mL T2 = ??

  24. Learning Check A gas has a volume of 675 mL at 35°C and 0.850 atm pressure. What is the temperature in °C when the gas has a volume of 0.315 L and a pressure of 802 mm Hg?

  25. Learning Check A balloon has a volume of 785 mL on a fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon?

  26. What about this one? A sample of neon gas used in a neon sign has a volume of 15 L at STP. What is the volume (L) of the neon gas at 2.0 atm and –25°C?

  27. Ideal Gas Law • Avogadro's hypothesis was that gases at the same temperature and pressure have the same number of molecules. • Adds moles (n) to the mix.

  28. PV = nRT • P = pressure in atm • V = volume in L • n = number of moles • R = the gas constant, 0.0821 L-atm/mol-K • T = temperature in K

  29. Try this… • Ex. 2 moles of O2 are placed in a 10L container at 20C. What is the pressure?

  30. Try this… • Ex. How many moles of H2 must be put into a 0.2L container at 25C to achieve 1.5atm of pressure?

  31. Try this… • What is the temperature of 50g of CO2 in a 5L container at 500 torrs?

  32. Dalton’s Law of Partial Pressure—when several gases are mixed together in a container: • They _______________________________________. • Each gas _______________________________________. • So… • Total Pressure = sum of partial pressures of each gas • P(total) = P(gas A) + P(gas B) + P(gas C)

  33. Ex. Gas A exerts a pressure of 1.5atm in a 2L container. Gas B exerts a pressure of 2atm in the same container. What is the total pressure? • Ex. Three gases are in a sealed container. The total pressure in the container is 800 torrs. If gas A exerts a pressure of 200 torrs and gas B exerts a pressure of 100 torrs, what pressure does gas C exert?

  34. Avogadro’s Hypothesis • if two gases have the same temperature, pressure and volume, they will have the same number of particles or moles. • one mole of gas at STP has a molar volume of 22.4L 1 mole = 22.4 L

  35. Ex. How many liters will 2.0 moles N2O occupy at STP?

  36. Ex. How many moles of hydrogen gas are there in 15.8L?

  37. Gas Stoichiometry • the same as regular stoichiometry, but using molar volume (22.4 L = 1 mole) 1 mole = 22.4 L 1 mole = 6.02 x 1023 representative particles 1 mole = the molar mass of a substance

  38. At STP, how many liters of O2 will be produced by the decomposition of 25g of KClO3? • 2 KClO3 2KCl + 3O2

  39. Ex. How many grams of H2O will be produced by the addition of 5L H2 to excess O2 at STP?

  40. If 100mL of hydrogen are produced from zinc reacting with HCl at STP, what mass of zinc is required?

  41. The End!

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