Applied Chapter 12.1 : Characteristics of Gases

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Applied Chapter 12.1 : Characteristics of Gases

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

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