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Kinetic Molecular Theory and Avagadro’s Theory

Kinetic Molecular Theory and Avagadro’s Theory. Chem 20 Chapter 4.2 Mr. Freiman. Kinetic Molecular Theory. Kinetic Molecular Theory explains kinetic energy Theory states that the SMALLEST particles of a substance are in continuous motion. Solids – molecules very close

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Kinetic Molecular Theory and Avagadro’s Theory

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  1. Kinetic Molecular Theory and Avagadro’s Theory Chem 20 Chapter 4.2 Mr. Freiman

  2. Kinetic Molecular Theory • Kinetic Molecular Theory explains kinetic energy • Theory states that the SMALLEST particles of a substance are in continuous motion

  3. Solids – molecules very close together. Motion is VIBRATIONAL only. Liquids – molecules close together, but can glide over one another. Motion is VIBRATIONAL, ROTATIONAL, And TRANSLATIONAL. Gases – molecules NOT close together. Motion is TRANSLATIONAL.

  4. Gases and Kinetic Molecular Theory • The properties of gases are supported by the kinetic molecular theory • A) gases are compressible  if the volume of gas is mostly empty space, you can force particles closer together • B) gas pressure  pressure is the amount of collisions between gas particles and wall of container

  5. C) Boyle’s Law  if volume is reduced, gas particles will collide more frequently with container resulting in INCREASED pressure • D) Charles’ Law  if temp is increased, gas particles will spread apart (increase volume) • E) Combined Law  if volume is fixed, increase in temperature will increase molecular motion causing more collisions resulting in INCREASED pressure

  6. Go to http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm

  7. Law of Combining Volumes • Joseph Gay-Lussac • Colleague of Charles • Measured volumes of gases in reactions • Observed that at same temp and pressure, gas reactants and products in a reaction are in SIMPLE RATIOS of WHOLE NUMBERS!

  8. Example • Decomposition of water results in volumes of hydrogen and oxygen in 2:1 ratio.

  9. Avagadro’s Theory • Relationship between VOLUME ratios and COEFFICIENT ratios • “equal volumes of gases contain equal numbers of molecules” • N2 + 3H2 + 2NH3 • Coefficients are in 1:3:2 ratio • Moles in 1:3:2 ratio • Volume in 1:3:2 ratio

  10. Example

  11. Molar Volume Chapter 4.3

  12. Molar Volume of Gases • Molar volume is the volume that one mole of gas occupies at a specified temperature and pressure. • Molar volume is the SAME for all gases at the same temperature and pressure • SATP: molar volume of a gas is 24.8 L/mol • STP: molar volume of a gas is 22.4 L/mol

  13. Why use Molar Volume? • Molar volume is easier than using Molar Mass • Mass is hard to measure for a gas! • Molar volume can help us convert moles of a gas and volume.

  14. Formula • n = v/V • n = moles • v = volume (L) • V = molar volume (L/mol)

  15. Example • What amount in moles of oxygen is available for a combustion reaction in a volume of 5.6 L at STP? • n = v/V • n = (5.6 L) / (22.4 L/mol) • n = 0.25 mol

  16. Example 2 • What volume of oxygen would 3.5 moles of carbon dioxide gas occupy at SATP?

  17. Molar Volume and Molar Mass • What happens when you are using the MASS of a gas? • Masses are used in the transportation of gases • Use Molar Volume AND Molar Mass • n = m/M • n = v/V

  18. Example • What volume does 3.50g of helium gas occupy at SATP?

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