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Characteristics Of Gases


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Characteristics Of Gases

  1. 1. What Do You Think of When you Hear The Word “Gas”
  2. 2. Characteristics of Gases <ul><ul><ul><li>Objectives : </li></ul></ul></ul><ul><ul><ul><ul><li>describe the general properties of gases </li></ul></ul></ul></ul><ul><ul><ul><ul><li>define pressure, know the SI unit for pressure, convert between standard units of pressure </li></ul></ul></ul></ul>
  3. 3. Characteristics of Gases <ul><li>Daily Questions: </li></ul><ul><ul><li>Among the states of matter, what is unique about gases? </li></ul></ul><ul><ul><li>Do gases have mass and weight? How can you tell? </li></ul></ul><ul><ul><li>Gases are considered fluids – why? </li></ul></ul>
  4. 4. Characteristics of Gases <ul><li>Proficient Students: </li></ul><ul><ul><li>can describe at least four characteristics of gases that differentiate them from other states of matter </li></ul></ul><ul><ul><li>can successfully convert between pascals, atm, mm Hg, and psi </li></ul></ul>
  5. 5. Characteristics of Gases <ul><li>Advanced Students: </li></ul><ul><ul><li>can complete all of the proficient student work AND answers the question, </li></ul></ul><ul><ul><ul><li>“ Why is atmospheric pressure greater at lower altitudes than at higher altitudes? ” </li></ul></ul></ul>
  6. 6. Properties of Gases <ul><li>Gases are fluids </li></ul><ul><ul><li>fluid means: “any substance that can flow” </li></ul></ul><ul><li>Gas particles flow because they are relatively far apart and therefore can move past each other easily </li></ul>
  7. 7. Properties of Gases <ul><li>Gases have low density </li></ul><ul><ul><li>because of the relatively large distances between gas particles, most of the volume occupied by gas is empty space </li></ul></ul><ul><ul><li>this low density also means </li></ul></ul><ul><ul><li>that gas particles travel </li></ul></ul><ul><ul><li>relatively long distances </li></ul></ul><ul><ul><li>before colliding with each </li></ul></ul><ul><ul><li>other </li></ul></ul>
  8. 8. Properties of Gases <ul><li>Gases are highly compressible </li></ul><ul><ul><li>If you fill a syringe with a liquid, it requires great force to compress the liquid with the plunger </li></ul></ul><ul><ul><li>A syringe filled with gas can be compressed with just a little effort. </li></ul></ul><ul><ul><ul><li>Why do you think this is? </li></ul></ul></ul>
  9. 9. Properties of Gases <ul><li>Gases completely fill a container </li></ul><ul><ul><li>Gases have neither a definite volume nor a definite shape </li></ul></ul><ul><ul><ul><li>gas particles are far enough apart that they do not attract each other as much as particles of solids and liquids do, therefore they expand to fill any container they are placed in </li></ul></ul></ul>
  10. 10. Properties of Gases
  11. 11. Measuring Pressure <ul><li>Pressure = force/area </li></ul><ul><ul><li>so, to find pressure, you need to know the force and the area over which that force is exerted </li></ul></ul><ul><li>SI unit of force = Newton </li></ul><ul><ul><li>1 Newton = 1 kg x 1 m/s 2 </li></ul></ul><ul><li>SI unit for pressure = Pascal (Pa) </li></ul><ul><ul><li>A pascal is the force of 1 newton applied over an area of one square meter </li></ul></ul><ul><li>1 Pa = 1N/1m 2 </li></ul>
  12. 12. Measuring Pressure <ul><li>1 Pa is a small amount of pressure. </li></ul><ul><li>Consider a layer of water that is 0.102 mm deep over an area one square meter </li></ul><ul><ul><li>the pressure would be one Pa </li></ul></ul><ul><li>Pressure is measured with a barometer </li></ul>
  13. 13. Measuring Pressure <ul><li>Barometers measure pressure in mm of Hg </li></ul><ul><li>average air pressure at sea level = 760 mm Hg </li></ul><ul><li>760 mm Hg = 1 atm </li></ul><ul><li>1 atm = 101325 Pa </li></ul>
  14. 14. Measuring Pressure <ul><li>There are many units for measuring pressure – power tools that run off of an air compressor often measure pressure in psi </li></ul><ul><li>psi – pounds per square inch </li></ul><ul><li>because Evangelista Torricelli invented the barometer, physicists created a unit of pressure and named it the torr . </li></ul>
  15. 15. Measuring Pressure <ul><li>Because temperature and pressure both affect how a gas behaves, scientists decided to stop the madness and define a set of conditions called “STP” </li></ul><ul><li>STP = standard temperature and pressure </li></ul><ul><li>STP = 0°C and 1 atm </li></ul>