copyright©2000 by houghton mifflin company. all rights reserved. 1 gases

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  • Slide 1
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 1 Gases
  • Slide 2
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 2 A Gas 4 Uniformly fills any container. 4 Can be compressed. 4 Mixes completely with any other gas 4 Exerts pressure on its surroundings. 4 Can diffuse into other gases. 4 Can be described in terms of its volume, temperature, pressure, and the amount present.
  • Slide 3
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 3 Pressure 4 is equal to force/unit area 4 SI units = Newton/meter 2 = 1 Pascal (Pa) 4 1 standard atmosphere = 101,325 Pa 4 1 standard atmosphere = 1 atm = 760 mm Hg = 760 torr
  • Slide 4
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 4 A Torricellian Barometer At sea level, latitude 45 o north (or south), the average atmospheric pressure supports a column of mercury 760 mm high in a simple mercury barometer at 0 o C This average pressure is called one atmosphere.
  • Slide 5
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 5 The Effects of Decreasing the Volume of a Sample of Gas at Constant Temperature
  • Slide 6
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 6 Boyles Law * Pressure Volume = Constant (T = constant) P 1 V 1 = P 2 V 2 (T = constant) V 1/P (T = constant) ( * Holds precisely only at very low pressures.)
  • Slide 7
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 7 Plotting Boyles Data from Table 5.1
  • Slide 8
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 8 A Plot of PV versus P for Several Gases at Pressures Below 1 ATM
  • Slide 9
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 9 A gas that strictly obeys Boyles Law is called an ideal gas.
  • Slide 10
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 10 Example: Boyles Law At 25 o C, a sample of oxygen occupies 100. mL under a pressure of 380. torr. What volume would it occupy under a pressure of 1.00 atm at the same temperature?
  • Slide 11
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 11 Answer 50.0 mL
  • Slide 12
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 12 Example At 100. o C a sample of neon occupies 200. mL under a pressure of 4.00 atmospheres. What must the pressure be for it to occupy 800. mL at 100. o C?
  • Slide 13
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 13 Answer 1.00 atm.
  • Slide 14
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 14 The Effects of Increasing the Temperature of a Sample of Gas at Constant Pressure
  • Slide 15
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 15 Charless Law The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin. V = bT (P = constant) b = a proportionality constant
  • Slide 16
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 16 Charless Law
  • Slide 17
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 17 Amazing Experiments have shown that when a 273 mL sample of gas at 0 o C is heated to 1 o C, its volume increases by 1 mL to 274 mL. Conversely each degree the gas is cooled its volume decreases 1 mL. What will the volume of the gas be at 273 o C?
  • Slide 18
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 18 Plots of V Versus T (C) for Several Gases
  • Slide 19
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 19 The Kelvin Temperature Scale The temperature at 273 o C, the lowest temperature possible is known as absolute zero. It is the basis of the Kelvin (absolute) temperature. K = o C + 273
  • Slide 20
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 20 Plots of V Versus T
  • Slide 21
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 21 Example Charles Law A sample of hydrogen, H 2, occupies 100. mL at 25 o C and 740. torr. What volume would it occupy at 50.0 o C and 740. torr?
  • Slide 22
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 22 Answer 108 mL
  • Slide 23
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 23 Example A sample of oxygen, O 2, occupies 200. mL at 100. o C and 1.00 atm. At what temperature ( o C) will the oxygen occupy 400. mL if the pressure remains constant?
  • Slide 24
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 24 Answer 746 K 473 o C
  • Slide 25
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 25 The Effects of Increasing the Temperature of a Sample of Gas at Constant Volume: Whos Law?
  • Slide 26
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 26 Gay-Lussacs Law P 1 P 2 T1T1 T2T2 =
  • Slide 27
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 27 Combined Gas Law Boyles and Charles Laws can be combined together into the following mathematical expression: P 1 V 1 = P 2 V 2 T 1 T 2
  • Slide 28
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 28 A very convenient form: V 2 = V 1 P 1 T 2 P 2 T 1 The relationship has six variables. If any five are known, the sixth can be calculated.
  • Slide 29
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 29 Example A sample of nitrogen, N 2, occupies 200. mL at 57 o C under a pressure of 840. torr. What volume would it occupy at 0 o C and 1.00 atm pressure?
  • Slide 30
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 30 Answer 183 mL
  • Slide 31
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 31 Example A sample of methane, CH 4, the main component of natural gas occupies 400. mL at 96 o C under a pressure of 0.500 atm. What volume would it occupy at 0 o C under a pressure of 1200 torr?
  • Slide 32
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 32 Answer 93.7 mL
  • Slide 33
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 33 Avogadros Law For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures). V = an a = proportionality constant V = volume of the gas n = number of moles of gas
  • Slide 34
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 34 Standard Temperature and Pressure STP P = 1 atmosphere T = C The molar volume of an ideal gas is 22.42 liters at STP
  • Slide 35
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 35 A Mole of Any Gas Occupies a Volume of Approximately 22.4 L at STP
  • Slide 36
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 36 Example What volume does 36.3 g of oxygen, O 2, occupy at STP?
  • Slide 37
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 37 Answer 25.4 L
  • Slide 38
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 38 Molecular Weight Application of the gas laws provides a method of calculating the molecular weight of a gas. This plus elemental analysis provides mechanism for determining molecular formula
  • Slide 39
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 39 Example If 2.00 g of a gas occupies 560.mL at STP, what is its molecular weight?
  • Slide 40
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 40 Answer 80.0 g/mol
  • Slide 41
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 41 Example A compound containing only carbon and hydrogen is 80.0% C and 20.0% H by mass. At STP 280. mL of the gas weighs 0.375 g. What is the molecular formula for the compound?
  • Slide 42
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 42 Answer C2H6C2H6
  • Slide 43
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 43 Ideal Gas Law 4 An equation of state for a gas. 4 state is the condition of the gas at a given time. 4 Can be determined by combining Boyles Law, Charles Law, and Avogadros Law
  • Slide 44
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 44 Ideal Gas Law PV = nRT R = proportionality constant = 0.0821 L atm mol P = pressure in atm V = volume in liters n = moles T = temperature in Kelvins Holds closely at P < 1 atm
  • Slide 45
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 45 Example What volume does 48.0 g of methane, CH 4, occupy at 140. o C under a pressure of 1280 torr?
  • Slide 46
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 46 Answer 60.4 L
  • Slide 47
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 47 Example A 250. mL flask conta

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