Applied Chapter 12.1 : Characteristics of Gases
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Applied Chapter 12.1 : Characteristics of Gases

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Applied Chapter 12.1 : Characteristics of Gases Applied Chapter 12.1 : Characteristics of Gases Presentation Transcript

  • Chapter 12.1
    Characteristics of Gases
  • Describe the general properties of gases.
    Define pressure, give the SI unit for pressure, and convert between standard units of pressure.
    Relate the kinetic-molecular theory to the properties of an ideal gas.
    Objectives:
  • Kinetic-Molecular Theory (KMT)
    • ·       
    Based on the idea that particles of matter are always in motion.
    Provides a model of an ideal gas
    Imaginary gas that perfectly fits all the assumptions of the kinetic-molecular theory.
    KMT is based on the following 5 assumptions:
    Gases consist of large numbers of particles that are far apart relative to their size.
    • Volume of gas particles occupy a volume usually about a thousand times greater than liquid and solid particles.
  • Collisions between gas particles and between particles and container walls are elastic collisions.
    • Elastic collisions are ones in which there is no net loss of kinetic energy.
    Gas particles are in continuous, rapid, random motion. They therefore possess kinetic energy.
    • Kinetic energy is the energy of motion.
  • There are no forces of attraction or repulsion between gas particles.
    • Think of gas particles as small billiard balls, when they collide , they do not stick together, they bounce apart immediately.
    The average kinetic energy of gas particles depends on the temperature.
    • Higher the temperature, the faster the particles move
  • Kinetic-molecular theory and the nature of gases
    Expansion:
    • Gases do not have definite shape nor volume
    • The expand to fill container and take it’s shape and volume
    Kinetic-moleculartheory
    Gas particles move rapidly in all directions (assumption 3) without significant attraction or repulsion between them ( assumption 4)
  • Fluidity
    • Ability to flow
    • Liquids and gases are considered fluids because they both flow
    Kinetic-moleculartheory
    Low Density
    • Density of a gas is 1/1000ththat of liquid or solids.
    Animation
    Kinetic-moleculartheory
    Particles are so much farther apart in a gaseous state (assumption 1).
  • Compressibility
    • Crowding particles closer together.
    Kinetic-moleculartheory
    Gas particles are initially far apart (assumption 1), allowing the particles to be crowded together.
    Diffusion
    • Spontaneous mixing of the particles of two substances caused by their random motion.
    Kinetic-moleculartheory
    Random and continuous motion of the molecules (assumption 3) carries them throughout the available space.
  • Effusion
    • Process by which gas particles pass through a tiny opening.
    Animation of Effusion
    Source:
    http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/micro_effusion.html
  • Pressure
    To describe a gas fully, there are four measurable quantities
    Volume
    Temperature
    Number of molecules
    Pressure
  • Pressure and Force
    Pressure – defined as the force per unit area on a surface
    Pressure =
    force
    area
    Use pressure to explain why it is harder to cut this pineapple with the butter knife.
    How do snow shoes work?
    How does pressure help us skate?
  • force
    N
    Pressure =
    Units:
    area
    cm2
    H0w is a magician able to survive laying on a bed of nails?
  • Atmospheric Pressure :
    Blanket of air surrounding earth, exerting pressure
  • Barometer:
    Device used to measure atmospheric pressure.
    At OoC, atmosphere can support 760 mm column of mercury.
    Units of Pressure:
    1 atmosphere or 1 atm
    millimeters mercury ormm Hg
    torr (in honor of EvangelistaTorricelli)
    Pascal, Pa - pressure exerted by a force of one Newton acting on an area of one square meter.
    Conversions
    1 atm = 760 mm Hg
    1 torr = 1 mm Hg
    1 atm = 760 torr
    1 atm = 1.013 25 x 105 Pa
    1 atm = 101.3 25 kPa
  • Standard Temperature and Pressure
    Scientists have agreed on standard conditions of :
    1 atm pressure and O0C
    Also known as STP
    Sample Problem 1
    The average atmospheric pressure in Denver, Colorado, is 0.830 atm. Express this pressure (a) in mm Hg and (b) in kPa.
    760 mm Hg
    0.830 atm
    x
    (a)
    =
    631 mm Hg
    1 atm
    101.325 kPa
    0.830 atm
    x
    (b)
    =
    84.1 kPa
    1 atm