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Gas Laws

Gas Laws. Borrowed from L . Scheffler Lincoln High School. 1. Properties of Gases. Variable volume and shape Expand to occupy volume available Volume, Pressure, Temperature, and the number of moles present are interrelated Can be easily compressed

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Gas Laws

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  1. Gas Laws Borrowed from L. Scheffler Lincoln High School Scheffler 1

  2. Properties of Gases • Variable volume and shape • Expand to occupy volume available • Volume, Pressure, Temperature, and the number of moles present are interrelated • Can be easily compressed • Exert pressure on whatever surrounds them • Easily diffuse into one another Scheffler 2

  3. Kinetic Molecular Theory • Matter consists of particles (atoms or molecules) that are in continuous, random, rapid motion • The volume occupied by the particles has a negligibly small effect on their behavior • Collisions between particles are elastic • Attractive forces between particles have a negligible effect on their behavior • Gases have no fixed volume or shape, but take the volume and shape of the container • The average kinetic energy of the particles is proportional to their Kelvin temperature Scheffler 3

  4. Maxwell-Boltzman Distribution • Molecules are in constant motion • Not all particles have the same energy • The average kinetic energy is related to the temperature • An increase in temperature spreads out the distribution and the mean speed is shifted upward Scheffler 4

  5. The distribution of speeds of three different gases at the same temperature Velocity of a Gas The distribution of speeds for nitrogen gas molecules at three different temperatures Scheffler 5

  6. Barometer • The mercury barometer was the basis for defining pressure, but it is difficult to use or to transport • Furthermore Mercury is very toxic and seldom used anymore • Most barometers are now aneroid barometers or electronic pressure sensors, Scheffler 6

  7. Mercury Barometer • Used to define and measure atmospheric pressure • On the average at sea level the column of mercury rises to a height of about 760 mm. • This quantity is equal to 1 atmosphere • It is also known as standard atmospheric pressure Scheffler 7

  8. Pressure Units & Conversions • The above represent some of the more common units for measuring pressure. The standard SI unit is the Pascal or kilopascal. (kPa) • The US Weather Bureaus commonly report atmospheric pressures in inches of mercury. • Pounds per square inch or PSI is widely used in the United States. • Most other countries use only the metric system. Scheffler 8

  9. Standard Temperature and Pressure • Standard Temperature and Pressure or STP= 0oC or 273.15 Kelvin and a pressure of 1 atmosphere. *Note: if using STP in a calculation, must use Kelvin! Why? • This is used as a reference point when comparing quantities of gases • Gases are seldom measured at exactly these conditions. • We need to be able to compute the volume at various temperature and pressures 9 Scheffler

  10. Standard Temperature and Pressure (STP) The volume of a gas varies with temperature and pressure. Therefore it is helpful to have a convenient reference point at which to compare gases. For this purpose standard temperature and pressure are defined as: Temperature = 0oC 273 K Pressure = 1 atmosphere = 760 torr = 101.3 kPa This point is often called STP Scheffler 10

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