1. Ch. 5 Gases!!!!!

2. Pressure conversions O Pressure – force per unit area O Can be measured in atm, mmHg, torr, kPa, psi O 1atm =760mmHg = 760torr = 101.3kPa= 14.7psi O Measured with a barometer (atmospheric pressure) or a manometer (pressure within a container)

3. Main variables with gases O Pressure (P) O Volume (V) O Temperature (T) O Moles (n) O Ideal gas constant (R) = 0.08206

4. Boyles, Charles, Gay Lussac, Combined, Avogadros O Boyles: P 1 V 1 = P 2 V 2 O Charles: V 1 / T 1 = V 2 / T 2 O Gay Lussac: P 1 / T 1 = P 2 / T 2 O Combined: P 1 V 1 = P 2 V 2 T 1 T 2 O Avogadro: V 1 /n 1 = V 2 /n 2

5. Sample Questions 1. A balloon is filled to a volume of 7.00 x 10 2 mL at a temperature of 20.0°C. The balloon is then cooled at constant pressure to a temperature of 1.00 x 10 2 K. What is the final volume of the balloon?

6. Sample Questions 2. An 11.2-L sample of gas is determined to contain 0.50 mol N 2. At the same temperature and pressure, how many moles of gas would there be in a 20.0L sample?

7. Sample Questions 3. Suppose two 200.0L tanks are to be filled separately with the gases helium and hydrogen. What mass of each gas is needed to produce a pressure of 135 atm in its respective tank at 24°C?

8. Ideal Gas Law O PV = nRT O What units do each of the variables have to be in for this law? O Sample Question: A 5.0L flask contains 0.60g of O 2 at a temperature of 22°C. What is the pressure (in atm) inside the flask?

9. Gas Stoichiometry O 1 mole of ANY gas at STP = 22.4L O 22.4L is the “molar volume” of an ideal gas O Use this conversion to skip using the ideal gas law O Sample problem: A sample of nitrogen gas has a volume of 1.75L at STP. How many moles are present?

10. Molar Mass of a Gas O Molar mass = dRT P O d = density (g/L) O R = ideal gas constant O T = temperature O P = pressure O Sample: The density of a gas was measure at 1.50atm and 27°C and found to be 1.95g/L. Calculate the molar mass of the gas.

11. Dalton’s Law of Partial Pressures O P total = P 1 + P 2 + P 3 … O P 1, P 2 and P 3 are called partial pressures O P total can also be calculated if you know the total number of moles (n total ) O P total = n total (RT/V) O Mole fraction is also important to this O Mole fraction (χ 1 ) = n 1 /n total O Mole fraction is directly related to partial pressure: χ 1 = n 1 /n total = P 1 /P total

12. Dalton’s Law Sample Question 1. The partial pressure of oxygen was observed to be 156 torr in air with a total atmospheric pressure of 743 torr. Calculate the mole fraction of O 2 present.

13. Another Sample Question 1. Mixtures of He and O 2 can be used in scuba diving tanks to help prevent the “bends.” For a particular dive, 46L He at 25°C and 1.0atm and 12L O 2 at 25°C and 1.0atm were pumped into a tank with a volume of 5.0L. Calculate the partial pressure of each gas and the total pressure in the tank at 25°C.