1. Gases

2. Pressure Pressure is defined as the force applied over a given area. Barometric pressure is given on weather reports and is typically reported in a unit called millimeters of mercury (mm Hg) At sea level, the pressure is about 760 mm Hg. Other pressure units exist such as Pascals(SI unit), atmospheres, and bar. 1 atm = 760 mm Hg = 101.325 kPa = 1.01325 bar We can use the above ultra mega equation to convert between pressure units. Example: Convert 635 mm Hg into atm, bars, and kPa.

3. Practice Rank the following pressures in decreasing order of magnitude: 75 kPa, 250 mm Hg, 0.83 bar, and 0.63 atm.

4. Boyle’s Law The first gas law we will look at relates pressure and volume. The relationship only works if temperature and the amount of gas remain constant. Pressure increases as the volume decreases. They are inversely proportional. P 1 V 1 =P 2 V 2 Example: A sample of nitrogen in a 65.0 L air bag has a pressure of 745 mm Hg. If the sample is transferred to a 25.0 L bag, what is the new pressure?

5. Practice A sample of CO2 with a pressure of 55 mm Hg in a volume of 125 mL is compressed to a pressure of 78 mm Hg. What is the new volume?

6. Assignment Page 546 2, 4, 5, 6

7. https://www.youtube.com/watch?v=O MG6asig0hs Write a reflection to the video and explain the observed changes.

8. Charles’ Law

9. Practice A balloon with a volume of 45 L at 25°C is cooled to -10°C. What is the final volume?

10. Combined Gas Law

11. Practice A 22 L cylinder of helium is at a pressure of 150 atm and 31°C. How many 5.0 L balloons can you fill if the pressure is 755 mm Hg at 22°C?

12. Assignment Page 546 7, 8, 10, 12, 14

13. Avogadro’s Hypothesis The volume of a gas is directly proportional to the amount of gas (moles) if pressure and temperature remain constant. Example: N 2 + 3H 2 → 2NH 3 If you have 15.0 L of hydrogen, what volume of nitrogen reacts? How many liters of ammonia form?

14. Practice If 22.4 L of CH 4 are burned, what volume of oxygen reacted? What volumes of each product are produced?

15. Ideal Gas Law

16. Practice If an air balloon has 1300 mol of H 2. If the temperature was 23°C and the pressure was 750 mm Hg, what was the volume?

17. Density and Molar Mass We can derive an equation that relates the density to the molar mass of a gas. As you know density = mass / volume and PV=nRT We substitute mass/molar mass (m/M) for moles: PV=(m/M)RT We can rearrange the equation to get d = M/V = PM/RT Example: Calculate the density of carbon dioxide at STP. Standard temperature is 0°C and standard pressure is 1 atm.

18. Example The density of a gas is 5.02 g/L at 15°C and 745 mm Hg. What is its molar mass?

19. Assignment: Page 546 15, 16, 18, 20, 22, 24, 26

20. Example The empirical formula for a chlorofluorocarbon (CFC) is CHF 2, Find the molecular formula if a 0.100 g sample exerts 70.5 mm Hg in a 256 mL container at 22.3 °C.

21. Practice A 0.105 g sample of a gaseous compound has a pressure of 561 mm Hg in a 125 mL container at 23.0 °C. What is the molar mass?

22. Gas Laws and Stoichiometry We can use gas laws to find moles, then calculate grams using stoichiometry. Example: If an air bag has a pressure of 829 mm Hg at a temperature of 22.0 °C and the bag has a volume of 45.5 L, what mass of sodium azide, NaN 3 should be used? 2NaN 3 → 2 Na + 3 N 2

23. Practice If 355 L of hydrogen gas at 25 °C and 542 mm Hg is combined with excess nitrogen gas, what amount of ammonia, in moles, can be produced? If this amount of ammonia is stored in a 125 L tank at 25 °C, what is the pressure of the gas?

24. Assignment Page 547 28, 30, 32, 36

25. Partial Pressures

26. Example Halothane, C 2 HBrClF 3 is a common anesthetic. If the pressure of a mixture of 15 g of halothane and 23.5 g of oxygen gas is 855 mm Hg, what is the partial pressure of each gas?

27. Practice The mixture from the example is placed in a 5.00 L tank at 25.0 °C. What is the pressure of the gas mixture? What are the partial pressures? Give all pressures in mm Hg.

28. Kinetic-Molecular Theory The theory explains the behavior of the particles in a gas. The theory is made of the following postulates: ◦Gases consist of particles whose separation is greater than the size of the particles. ◦The particles are in continual, random, and rapid motion. They collide with each other and the walls of the container without losing energy. ◦The average kinetic energy of the particles is proportional to the temperature. Not all particles in a sample have the same kinetic energy. There is a range of energies possible that widens as temperature increases.

29. Root-Mean-Square Speed

30. Assignment Page 548 38, 40, 42, 44, 46

31. Diffusion Diffusion causes the molecules to naturally mix when a new gas is introduced into a container. If your mother is preparing a delicious meal in the kitchen, this is the reason you can enjoy the glorious aroma.

32. Effusion

33. Real Gases All of the calculations we have done were done assuming we had ideal gases. There is no such thing as an ideal gas, but it is much easier to perform the calculations that way. The main difference between real and ideal gases is that real gases have forces between their particles. There is also the fact that real gas molecules occupy volume, which has a bigger effect at high pressure.

34. Assignment Page 548 48, 50, 58, 64, 70, 94, 96, 98