1. Kinetic Theory and Gases

2. Objectives Use kinetic theory to understand the concept of temperature. 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 energy (or KE): the energy of motion; depends on both the mass and speed of the moving particles temperature (T): a measure of the average KE of all the particles in a substance NOT T-E-M-P ! Kinetic Energy number of particles

4. Kelvin Scale absolute zero: the coldest possible T; there is no molecular motion; KE = 0 (= -273 o C or 0 Kelvin) K = o C + 273 o C = K - 273 Kelvin temperature is directly proportional to the KE! 0 o C ≠ 0 KE 0 K = 0 KE 200K has 2X more KE than 100K KE T

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 pressure: force applied over an area metric pressure unit: 1 pascal (Pa) = 1 N/m 2 barometer: instrument that measures atmospheric pressure Atmospheric pressure is 14.70 lbs/in 2 at sea level. spheres DEMO ! Gases exert pressure by collisions.

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

8. CAN SMASH Have about 1 inch of water in the bowl plus at least one large ice cube. Remove tab from rinsed can. Place about 1/8” of water in the can. Hold can with tongs—palm up! Heat the water over the burner, shaking can regularly. Allow water to boil—steam forms. Shake out any excess water. Heat briefly again. Plunge top of can into the ice water!

9. 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.

10. The G-U-E-S-S Method G = list the “given” values U = list the “unknown” E = find the correct equation S = solve for the unknown (use algebra!) S = substitute the values and solve

11. Boyle’s Law Boyle’s Law (T is constant ) force (F) relates to temperature (T) area (A) relates to volume (V) P and V are inversely proportional temperature (in K scale) volume At constant temperature, 7.5 L of air at 89.6 kPa is compressed to 2.8 L. What is the new pressure? Demo: balloon in vacuum

12. Charles’s Law and the P-T Law Charles’s Law (P is constant ) V and T are directly proportional *must use Kelvin P-T Law (V is constant ) P and T are directly proportional *must use Kelvin Demos: hot squirt bottle, space modulator gun

13. Gas Law Problems (use GUESS method) (1) A 3.0 L balloon inside a -22 o C freezer is removed and placed into a room at 19 o C. What is the new volume if the pressure remains the same? What law was used? (2)A solid container of gas at STP is heated and the pressure increases to 158 kPa. What is the new temperature of the gas? What law was used?

14. 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.

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

16. More Gas Law Problems 1.What is the molar mass of a gas that has a mass of 0.35 g and occupies 165mL at 95 o C and 87.0 kPa? 2.How many moles of air are in a 3.2 L balloon under the current temperature and pressure conditions in this room? 3.What is the density of N 2 gas at 95 kPa and 25 o C?

17. 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.

18. Avogadro’s Law Avogadro’s Law: equal volumes of gases at the same T and P contain equal numbers of molecules (n) O2O2 HeCO 2 Why? Look at the Ideal Gas Law!

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

20. 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 CO 2 at 23 o C and 89.5 kPa are formed when a 468 g container of C 3 H 8 is burned? C 3 H 8 + 5 O 2 → 3 CO 2 + 4 H 2 O (2) How many liters of H 2 gas are formed when 0.25 g Na reacts with HCl at STP? 2Na + 2HCl → H 2 + 2NaCl