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Kinetic Theory and Gases

Kinetic Theory and Gases. Objectives. Use kinetic theory to understand the concepts of temperature and gas pressure. Be able to use and convert between the Celsius and Kelvin temperature scales. Kinetic Theory. kinetic theory : all matter is made of particles (atoms,

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Kinetic Theory and Gases

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  1. Kinetic Theory and Gases

  2. Objectives • Use kinetic theory to understand the concepts of temperature and gas pressure. • Be able to use and convert between the Celsius and Kelvin temperature scales.

  3. Kinetic Theory kinetic theory: all matter is made of particles (atoms, ions, molecules) that are in constant, random motion Kinetic Theory Applet kinetic energy (or KE): the energy of motion; depends on both the mass and speed of the moving particles number of particles temperature (T): a measure of the average KE of all the particles in a substance NOT T-E-M-P ! average KE ~ temperature

  4. Kelvin Scale absolute zero: the coldest possible temperature; there is no molecular motion (= -273oC or 0 Kelvin) K = oC + 273 oC = K - 273 Kelvin temperature is directly proportional to the KE! 0 K = 0 KE 0 oC ≠ 0 KE 600K is 2X more KE than 300K

  5. Objectives • Understand the concept of atmospheric pressure. • Be able to explain how a barometer works. • Be able to convert between pressure measurements.

  6. Gases and Pressure Gases exert pressure by collisions. pressure: force applied over an area metric pressure unit: 1 pascal (Pa) = 1 N/m2 14.70 pounds of air push down on each square inch of the earth’s surface (at sea level) spheres DEMO! barometer: instrument that measures atmospheric pressure

  7. Pressure Conversions standard pressure (P) = 14.70 psi = 760.0 mm Hg = 29.92 in Hg = 101.3 kPa = 1.000 atm standard temperature (T) = 0oC or 273 K STP: standard T and P What is the current pressure in kPa and atm?

  8. Objectives • Be able to use the pressure equation to explain pressure, temperature, and volume changes in gases. • Understand how to solve word problems using the “GUESS” method. • Be able to use the various gas laws to solve problems.

  9. The Gas Laws temperature (in K scale) • force (F) relates to temperature (T) • area (A) relates to volume (V) volume Boyle’s Law (constant T) P and V are inversely proportional Charles’s Law (constant P) P-T Law (constant V) V and T are directly proportional P and T are directly proportional

  10. Gas Law Problems Using GUESS Method (1) At constant temperature, 7.5 L of air at 89.6 kPa is compressed to 2.8 L. What is the new pressure? What law was used? • A 3.0 L balloon at 22oC is placed into a freezer at • -15oC. What is the new volume if the pressure remains • the same? What law was used? • A fixed volume of gas at STP is heated to 482oC. • What is the pressure in kPa at this temperature? What • Law was used?

  11. Objectives • Understand how the various gas law equations are derived. • Be able to use the ideal gas law, gas molar mass equation, and gas density equation to solve problems.

  12. More Gas Laws Combined Gas Law Gas Molar Mass Ideal Gas Law n = # moles Gas Density R = 8.31 kPaL/molK

  13. More Gas Law Problems • What is the molar mass of a gas that has a mass of 0.35 g and occupies 165mL at 95oC and 87.0 kPa? • How many moles of air are in a 3.2 L balloon under the current temperature and pressure conditions in this room? • What is the density of N2 gas at 95 kPa and 25oC?

  14. Objectives • Understand Avogadro’s law by considering the ideal gas law. • Be able to use the law of combining gas volumes to solve simple gas stoichiometry problems. • Be able to use the ideal gas law to solve more complex gas stoichiometry problems.

  15. Avogadro’s Law Avogadro’s Law: equal volumes of gases at the same T and P contain equal numbers of molecules (n) O2 He CO2 Why? Look at the Ideal Gas Law!

  16. Law of Combining Gas Volumes Coefficients can represent gas volumes if the reactants and products are at equal T and P. N2(g) + 3H2(g) → 2NH3(g) How many liters of H2 are needed to completely react with 2.5 L N2? Assume same T and P. 1 vol. 3 vol. 2 vol. 1 L 3 L 2 L

  17. Gas Stoichiometry g A → mol A → mol B → g B g A → mol A → mol B → L B (use V = nRT/P) • (1) How many liters of CO2 at 23oC and 89.5 kPa are • formed when a 468 g container of C3H8 is burned? • How many liters of H2 gas are formed when 0.25 g • Na reacts with HCl at STP?

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