1. Gaseous Mixtures Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

2. Gaseous Mixtures  Reading Assignment: Fine, Beall & Stuehr, Chapter 4.6-4.7  Gas Mixtures Mole fraction Dalton's Law of Partial Pressures Vapor pressure Wet gases

3. Mole Fraction  A = mol A mol A + mol B + mol C +... What is the mole fraction of each gas? A gas sample contains 3 moles of hydrogen and 2 moles of oxygen. The ratio of moles of a compound in a mixture to the total moles in the mixture.

4. Mole Fraction  H2H2 = moles H 2 moles H 2 + moles O 2 = 3 3 + 2 = 0.60  O2O2 = moles O 2 moles H 2 + moles O 2 = 2 3 + 2 = 0.40 The sum of the mole fractions in a mixture equals exactly 1

5. Partial Pressure The pressure a fixed amount of gas would exert if it were alone in a given volume at a given temperature.

6. Gas Bulb 3 liters, 2 atm2 liters, 1 atm What will happen when the stopcock is opened?

7. Gas Bulb What will happen to the pressure of the orange atoms? 3 liters, 2 atm2 liters, 1 atm

8. Gas Bulb What will be the pressure of the orange atoms?pressure Hint: Boyle’s Law 3 liters, 2 atm2 liters, 1 atm

9. Gas Bulb P · V = constant 2 atm · 3 L = 6 L· atm P orange · 5 L = 6 L· atm P orange = 6 L· atm / 5 L = 1.2 atm

10. Dalton's Law of Partial Pressures P total = P A + P B + P C +... The total pressure of a non-reacting gaseous mixture is the sum of the partial pressures of each gas in the mixture.

11. Gas Bulb What is the total pressure in the left bulb? 3 liters, 2 atm2 liters, 1 atm

12. Gas Bulb What is the total pressure in the left bulb? 1.6 atm What is the total pressure in the right bulb? 1.6 atm 3 liters, 2 atm2 liters, 1 atm

13. Dalton's Law of Partial Pressures What is the mole fraction of each gas? P A = P total ·  A What is the partial pressure of each gas?

14. Vapor Pressure  The pressure exerted by the vapor of a substance when in equilibrium with the substance. Even below their boiling point, liquids evaporate or vaporize and solids sublime.

15. Vapor Pressure Adding additional liquid does not increase the amount of vapor in the air. If a container is closed, then the liquid will only evaporate until the air is saturated with the vapor.

16. Vapor Pressure Is it possible for water to boil at room temperature? Boiling occurs when the vapor pressure of a liquid equals or exceeds the restraining pressure (e.g., atmospheric pressure)

17. Vapor Pressure of Water 0 20 40 60 80 100 01020304050 Temperature (°C) Pressure (torr) Increases non-linearly with increasing temperature.

18. Wet Gases Gases trapped by liquid displacement. The total pressure of the gas trapped by water displacement is equal to the partial pressure of the gas plus the vapor pressure of water at that temperature. Is the pressure of the trapped gas equal to, less than or greater than atmospheric pressure? P total = P gas + P water vapor