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Chapter 11

Chapter 11. Gas Laws. The Gas Phase. Gases have no distinct volume or shape. Gases expand to fill the volume of their container. Gas particles are miscible with each other. Evidence for gas particles being far apart : We can see through gases We can walk through gases

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Chapter 11

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  1. Chapter 11 Gas Laws

  2. The Gas Phase • Gases have no distinct volume or shape. • Gases expand to fill the volume of their container. • Gas particles are miscible with each other. • Evidence for gas particles being far apart : • We can see through gases • We can walk through gases • Gases are compressible • Gases have low densities

  3. The Air We Breathe

  4. Kinetic Theory of Gases • Gas particles are sizeless relative to the volume of the gas • Gas particles are in constant rapid motion • Gas particles have elastic collisions; means no kinetic energy is lost on impact. • The absolute temperature is directly proportional to the kinetic energy of a gas. • Gas particles have no attraction to each other; i.e. no inter particle froces. Kinetic Theory Postulates:

  5. Parameters Affecting Gases • Pressure (P); atm, mmHg, torr, lbs/in2 • Volume (V); L, mL • Temperature (T); K (only) • Number of Moles (n)

  6. Pressure Pressure is equal to force/unit area (P =F/A) lbs/in2 Force is a push which comes from gas particles striking a container wall

  7. Pressure Units • SI units = Newton/meter2 = 1 Pascal (Pa) • 1 standard atmosphere (atm) = 101,325 Pa • 1 atm =760 mm Hg • 1 atm = 760 torr (torr is abbreviation of mmHg) • 1 atm = 14.7 lbs/in2 • 1 atm = 1.013 barr • Barr = 100 kPa

  8. Measurement of Pressure What is above mercury?

  9. Measurement of Pressure

  10. Elevation and Atmospheric Pressure

  11. Pressure Measurement Is the atmosphere or the gas in the canister pushing harder? Open Tube Manometer = 15 mm

  12. Pressure Measurement Is the atmosphere or the gas in the canister pushing harder? Gas in the canister If the atmospheric pressure is 766 mm, then what is the pressure of the canister? Open Tube Manometer = 15 mm

  13. Pressure Measurement Is the atmosphere or the gas in the canister pushing harder? Gas in the canister If the atmospheric pressure is 766 mm, then what is the pressure of the canister? P = 766 + 15 = 781 mm (torr) Open Tube Manometer = 15 mm gas

  14. Pressure Measurement Open Tube Manometer Is the atmosphere or the gas in the canister pushing harder? gas

  15. Pressure Measurement Open Tube Manometer Is the atmosphere or the gas in the canister pushing harder? The atmosphere What is the pressure of the gas if the atmosphere is 766 mm? = 13 mm gas

  16. Pressure Measurement Open Tube Manometer Is the atmosphere or the gas in the canister pushing harder? The atmosphere What is the pressure of the gas if the atmosphere is 766 mm? 753 mm = 13 mm gas

  17. Pressure Measurement Open Tube Manometer Now what is pushing harder, the gas or the atomosphere? gas

  18. Pressure Measurement Open Tube Manometer Now what is pushing harder, the gas or the atmosphere? Neither, both the same. gas

  19. Pressure Measurement Open Tube Manometer Now what is pushing harder, the gas or the atmosphere? Neither, both the same. Is the gas canister empty? gas

  20. Pressure Measurement Open Tube Manometer Now what is pushing harder, the gas or the atmosphere? Neither, both the same. Is the gas canister empty? No, completely full of gas! gas

  21. Dalton’s Law of Partial Pressures • For a mixture of gases in a container • PTotal = P1 + P2 + P3 + . . .

  22. Boyles Law Consider a gas in a closed system containing a movable plunger. If the plunger is not moving up or down, what can be said about the pressure of the gas relative to the atmospheric pressure? Atm ● ● ● ●

  23. Boyles Law Suppose we add some red gas to the container, what would happen to the collisions of gas particles with container walls. Would they increase, decrease or stay the same? Atm ● ● ● ● ● ● ●

  24. Boyles Law Suppose we add some red gas to the container, what would happen to the collisions of gas particles with container walls. Would they increase, decrease or stay the same? More particles, more collisions, and more pressure. What happens to the plunger? Atm ● ● ● ● ● ● ●

  25. Boyles Law Suppose we add some red gas to the container, what would happen to the collisions of gas particles with container walls. Would they increase, decrease or stay the same? More particles, more collisions, and more pressure. What happens to the plunger? Atm ● ● ● ● ● ● ●

  26. Boyles Law The number of particles remain the same, but the surface area they have to strike increases, thus the number of collisions per square inch decrease as the plunger goes up exposing more surface area causing a decrease in pressure. ● ● ● ● ● ● ● ● ● ●

  27. Boyle’s Law P  1/V (T and n fixed) P  V = Constant P1V1 = P2V2 Pressure and volume are inversely proportional.

  28. Charles’s Law • The volume of a gas is directly proportional to Kelvin temperature, and extrapolates to zero at zero Kelvin. V  T (P & n are constant) V1 = V2 T1 T2

  29. Combined Gas Law • Combining the gas laws the relationship P T(n/V) can be obtained. • If n (number of moles) is held constant, then PV/T = constant. Temperature, K (only) Pressure: Atm, mmHg, Torr, PSI, KPa Volume: L, mL, cm3, …

  30. Example A balloon is filled with hydrogen to a pressure of 1.35 atm and has a volume of 2.54 L. If the temperature remains constant, what will the volume be when the pressure is increased to 2.50 atm? (2.54 L) (1.35 atm) (2.50atm)V2 = T1 T1 (1.35 atm) (2.54 L) V2 = Constant Temp. means T1=T2 (2.50atm) V2 = 1.37 L

  31. Example A sample of oxygen gas is at 0.500 atm and occupies a volume of 11.2 L at 00C, what volume will the gas occupy at 6.00 atm at room temperature (250C)?

  32. Ideal Gas Law PV = nRT R = universal gas constant = 0.08206 L atm K-1 mol-1 P = pressure in atm V = volume in liters n = moles T = temperature in Kelvin

  33. STP • “STP” means standard temperature and standard pressure • P = 1 atmosphere • T = 0C • The molar volume of an ideal gas is 22.42 liters at STP (put 1 mole, 1 atm, R, and 273 K in the ideal gas law and calculate V)

  34. Calculate the pressure of a 1.2 mol sample of methane gas in a 3.3 L container at 25°C. Example

  35. Calculate the pressure of a 1.2 mol sample of methane gas in a 3.3 L container at 25°C. Example 0.0821 L-atm Mole-K

  36. Calculate the pressure of a 1.2 mol sample of methane gas in a 3.3 L container at 25°C. Example 0.0821 L-atm Mole-K 3.3 L

  37. Calculate the pressure of a 1.2 mol sample of methane gas in a 3.3 L container at 25°C. Example 0.0821 L-atm 298 K Mole-K 3.3 L

  38. Calculate the pressure of a 1.2 mol sample of methane gas in a 3.3 L container at 25°C. Example 0.0821 L-atm 1.2 mole 298 K Mole-K 3.3 L

  39. Calculate the pressure of a 1.2 mol sample of methane gas in a 3.3 L container at 25°C. Example 0.0821 L-atm 1.2 mole 298 K = 8.9 atm Mole-K 3.3 L

  40. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas.

  41. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. 0.0821 L-atm mole-K

  42. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. 0.0821 L-atm 0.495 g mole-K

  43. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. mL 0.0821 L-atm 0.495 g mole-K 10-3 L

  44. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. mL 0.0821 L-atm 0.495 g mole-K 10-3 L 127 mL

  45. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. mL 760 torr 0.0821 L-atm 0.495 g mole-K atm 10-3 L 127 mL

  46. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. mL 760 torr 0.0821 L-atm 0.495 g mole-K atm 10-3 L 127 mL 754 torr

  47. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. mL 760 torr 371 K 0.0821 L-atm 0.495 g mole-K atm 10-3 L 127 mL 754 torr

  48. Example An experiment shows that a 0.495 g sample of an unknown gas occupies 127 mL at 98°C and 754 torr pressure. Calculate the molar mass of the gas. mL 760 torr 371 K 0.0821 L-atm 0.495 g mole-K atm 10-3 L 127 mL 754 torr = 120 g/mole

  49. Collecting a Gas Over Water

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