Ch 9 Text

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DesLee26
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192869
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Ch 9 Text
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2013-01-26 19:16:19
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CHM 112
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Gases: Their Properties and Behavior
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  1. solids
    substances whose constituent atoms, molecules, or ions are held rigidly together in a definite way, giving hte solid a definite volume and shape
  2. liquids
    constituent atoms or molecuels are held together less strongly, giving hte liquid a definite volume but a changeable and indefinite shape
  3. gases
    constituent atoms or molecules have little attraction for one another and are therefore free to move about in whatever volume is available
  4. __ and __ account for more than 99% by volume fo dry air. The remaining 1% is largely __, with trace amounts of several other substances also present. __ is present (.0385%)
    • nitrogen
    • oxygen
    • argon
    • carbon dioxide
  5. Gas mixtures are always __, meaning that they are __. 
    • homogeneous
    • uniform in composition
  6. Unlike liquids, which often fail to mix with one another and which may separate into distinct layers--oil and water, for example-- gases always mix completely
    a. true
    b. false
    a. true
  7. Gases are __. When pressure is applied, what happens to the volume?
    Solids and liquids, however, are nearly __, and even the application of great pressure does what to their volume?
    • compressible
    • the volume of a gas contracts proportionately
    • incompressible
    • changes their volume only slightly
  8. Why does homogeneous mixing and compressibility both occur?
    because molecules in gases are far apart
  9. Mixing occurs because what?
    In solids and liquids, molecules are packed closely together, where they are affected by various __ and __ forces that can __ their mixing. 
    • individual gas molecules have little interaction with their neighbors and the chemical identities of those neighbores are irrelevant
    • attractive
    • repulsive
    • inhibit
  10. One of the most obvious characteristics of gases is that they exert a measurable __ on the walls of their container.
    pressure
  11. What is pressure? 
    What is the formula?
    • force exerted per unit area
    • P=F/A= (m x a)/ A
    • where F is force, A (area), m(mass), a (acceleration)
  12. The SI unit for force is the __, and the SI unit for pressure is the __. 
    • Newton (N)
    • pascal (Pa)
  13. The mass of air in the atmosphere pressing down on the Earth's surface exerts what we call __.
    atmospheric pressure
  14. Because the pascal is an inconvenient size for most chemical measurements, the alternative pressure units __, __, and __, are most often used.
    • mm of mercury (mm Hg)
    • atm
    • bar
  15. the __, also called a __. is based on atmospheric pressure measurements using a mercury _.
    • mm Hg
    • torr
    • barometer
  16. Explain a barometer.
    a long, thin tube that is sealed at one end, filled with mercury, and inverted into a dish of mercury; some mercury runs from tube into dish until downward pressure of the mercury insidethe column is exactly balanced by the outside atmospheric pressure, which presses on the mercury in the dish and pushes it up the column
  17. In a barometer, the empty space above the mercury in the sealed end of hte tube is a __.
    vacuum
  18. Knowing the density of Hg and the acceleration due to gravity, its possible to calculate hte __.
    pressure exerted by the column of mercury 760 mm in height
  19. Why is the bar convenient?
    It is a power of ten of hte SI unit pascal
  20. Gas pressure inside a container is often measured using an open-end __, a simple instrument similar in principle to the mercury barometer.
    manometer
  21. explain a manometer.
    • U-tube filled with Hg, with one end connected to a gas-filled container and the other end open to the atmosphere
    • the difference between the pressure of the gas in the container and the pressure of the atmosphere is equal to the difference between the heights of hte mercury levels in the two arms of the U-tube
  22. Manometer:
    If the gas pressure inside the container is less than atmospheric, the mercury level is __.
    If the gas pressure inside the container is greater than atmospheric, the mercury level is __.
    • higher in the arm conncted to the container
    • higher in the arm open to the atmosphere
  23. True or False:
    Different gases show remarkably different physical behavior regardless of chemical makeup.
    • False: 
    • Different gases show remarkably similar physical...
  24. The physical properties of any gas can be defied by four variables: __(4)__
    The specific relationships among these four variables are called __, and a gas whose behavior follows the laws exactly is called an __.
    • pressure (P)
    • temp (T)
    • volume (V)
    • amount (number of moles- n)
    • gas laws
    • ideal gas
  25. Boyle's Law
    • volume of a fixed amount of gas at a constant temperature varies inversely with its pressure
    • ex: if gas pressure is doubled, hte volume is halved
    • in other words: the volume of an ideal gas varies inversely with pressure
  26. When V and P are plotted at constant temp and moles (Boyle's Law), what will the graph resemble?
    hyperbola
  27. Charles' Law
    • volume of a fixed amount of an ideal gas at a constant pressure vries directly with its absolute temperature
    • if gas temp in kelvin is doubled, the volume is doubled
    • in other words: volume of an ideal gas varies directly with absolute temperature
  28. How was absolute zero determined?
    using Charles's law and plotting volume versus temperature
  29. Avogadro's Law
    • the volume of an ideal gas at a fixed pressure and temperature depends on its molar amount. (The volume of an ideal gas varies directly with its molar amount.)
    • If the amount of the gas is doubled, the gas volume is doubled; if halved, the volume is halved.
    • V/n= k at constant T and P
  30. One mol of an ideal gas occupies a volume, called the __, of 22.414 L at 0 degrees C and exactly 1 atm pressure. 
    standard molar volume
  31. All three gas laws can be combined into a single statement called the __,which describes how the volume of a gas is affected by changes in pressure, temperature, and amount. When the values of any three of the variables P, V, T, and n are known, the value of the fourth can be calculated using the __. The proportionality constant R in the equation is called the __ and has the same value for all gases. 
    • ideal gas law
    • ideal gas law
    • gas constant
  32. Ideal Gas Law Formula
    • V= (nRT/P) 
    • OR
    • PV=nRT
  33. The specific conditions of 0 degrees Celcius and 1 atm pressur are said to represent __.
    standard temperature and pressure (STP)
  34. The name __ implies that there must be some gases whose behavior is __. In fact, there is no such thing as an ideal gas that obeys the equation perfectly under all circumstances.
    • ideal gas law
    • nonideal
  35. All real gases are __ to some extent and deviate slightly from the behavior predicted by the gas laws. 
    nonideal
  36. How are densities calculated?
    by weighing a known volume of a gas at a known temperature and pressure
  37. Using the __ to find the volume at __ and then dividing the measured mass by the volume gives the __ at __.
    • ideal gas law
    • STP
    • density
    • STP
  38. __, and therefore __, can also be calculated using the ideal gas law.
    • molar masses
    • molecular masses
  39. Just as the gas laws apply to all pure gases, regardless of chemical identity, they also apply to __ of gases, such as air. The __, __, __, and __ mixture are all related by the __.
    • mixtures
    • pressure
    • volume
    • temperature
    • amount of a gas mixture
    • ideal gas law
  40. Because the pressure of a __ at constant temperature and volume is proportional to its __, the pressure contribution from each individual gas in a mixture is also proportional to __. 
    • pure gas
    • amount
    • its amount in the mixture
  41. In other words, the __ exerted by a mixture of gases in a container at constant V and T is equat to the __ of each individual gas in the container, a statement known as __.
    • total pressure
    • sum of the pressures
    • Dalton's law of partial pressures
  42. Dalton's law of partial pressures
    Ptotal= P1+P2+P3+.. at constant V and T, where P1, P2,.. refer to the pressures each individual gas would have if it were alone.
  43. The individual pressure contributions of the various gases in the mixture, P1, P2, and so forth, are called __ and refer to the pressure each individual gas would exert if it were alone in the container. 
    partial pressures
  44. The concentration of any individual component in a gas mixture is usually expressed as a __.
    mole fraction
  45. What is the mole fraction?
    the number of moles of the component divided by the total number of moles in the mixture
  46. Mole Fraction Equation.
    Moles of component/ Total moles in mixture
  47. Assumptions of the Kinetic-molecular theory:
    One
    a gas consists of tiny particles, either atoms or molecules, movng about at random
  48. Assumptions of the Kinetic-molecular theory:
    two
    The volume of the particles themselves is negligible compared with the total volume of the gas. Most of the volume of a gas is empty space.
  49. Assumptions of the Kinetic-molecular theory:
    Three
    The gas particles act independently of one another; there are no attractive or repulsive forces between particles
  50. Assumptions of the Kinetic-molecular theory:
    Four
    • Collisions of the gas particles, either with other particles or with the walls of a container, are elastic. That is, the total kinetic energy of the gas particles is constant at constant T.
  51. Assumptions of the Kinetic-molecular theory:
    Five
    The average kinetic energy of the gas particles is proportional to the Kelivin temperature of the sample
  52. Gas pressure
    a measure of the number and forcefulness of collisions between gas particles and the walls of their container
  53. Temperature
    The higher the temp at constant n and P, the what?
    • a measure of the average kinetic energy of the gas particles
    • faster the gas particles move and the more room theey need to move around in order to avoid increasing their collisions with the walls of the container
  54. Total pressure of a fixed volume of gas depends only on the __.
    T and the total number of moles of gas n
  55. There is a __ among particles in a gas, a distribution that flattens out and moves to higher speeds as __.
    • broad distribution of speeds
    • temp increases
  56. Why is the actual path followed by a gas particle a random zigzag?
    an individual gas particle collides with another particle and bounces off in a different direction
  57. For helium at room temp and 1 atm pressure, the average distance between collisions, called the __, is only about 1000 atomic diameters.
    mean free path
  58. What are some consequences of the constant motion and high velocities of gas particles?
    gases mix rapidly when they come in contact
  59. mixing of different molecules by random molecular motion with frequent collisions
    diffusion
  60. gas molecules escape without collisions through a tiny hole into a vacuum
    effusion
  61. Graham's law
    • the rate of effusion of a gas is inversely proportional to the square root of its mass, m
    • - the lighter the molecule, the mroe rapidly it effuses
  62. Explain why differeent gases at the same temperature have the same average kinetic energy?
    because temperature is a measure of average kinetic energy and is independent of the gas's chemical identity
  63. Why is diffusion more complex than effusion?
    because of the molecular collisions that occur
  64. True or False:
    The behavior of a real gas is the same as that of an ideal gas.
    Explain your answer.
    • false:
    • different from that
    • kinetic-molecular theory assumes the volume of the gas particles themselves is negligible comapred with the total gas volume. This is valid at STP, but not at other ones.
    • It also says that there are no attractive or repulsive forces; there are!
  65. Both ways in which the behavior of real gases deviates from the ideal gas law can be dealt with mathematically by a modificaiton of the ideal gas law called the __, which uses two correction factors, called and b. Four legions of the atmosphere.
    van der Waals equation
  66. The temperature in the __, the region nearest the earth's surface, decreases regularly. 
    troposphere
  67. After the troposphere is the __, then the __, and the __. 
    • stratosphere
    • mesosphere
    • thermosphere
  68. What are the main causes of air pollution?
    release of unburned hydrocarbon molecules and the production of NO during combustion of petroleum products in older industrial plants
  69. What is acid rain?
    results primarily from production of sulfur dioxide

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