2. Final Exam Reminders: Date: Monday, December 14, 2009 Time: 8:00-10:30am Place: IRC 1 (Here) What to Bring: Calculator #2 Pencil 2 Pages (double-sided) of notes Make up Lab-On OWL, due at final exam Today Chapter 10: Gases Friday Chapter 11: Intermolecular Forces and the Liquid State (Fri.) December 9, 2009

3. Kinetic Molecular Theory & Gases Gas molecules far apart, always in motion, collide with walls of container (pressure) Temperature  Average Kinetic Energy  Higher temperature = higher average kinetic energy Kinetic energy and velocity are not the same  Higher molar mass will move slower at the same temperature Boltzmann distribution  Plot of molecular speed (x) vs. number of molecules (y)  Shows range of speeds in a collection of molecules

4. Gases- Equations from last time… Kinetic energy of one molecule Average Kinetic energy of many molecules Average speed of molecules

5. Gas Diffusion

6. Gas Effusion Graham’s Law of Effusion

7. Graham’s Law Example A sample of ethane, C 2 H 6, effuses through a small hole at a rate of 3.6 x 10 -6 mol/hr. An unknown gas, under the same conditions, effuses at a rate of 1.3 x 10 -6 mol/hr. Calculate the molar mass of the unknown gas.

8. Back to Pressure… Collisions between gas molecules and container exerts a force on container wall  More collisions and more energetic collisions = greater force = higher pressure Kinetic molecular theory gives conceptual framework for understanding the behavior of gases  P and n(P  n)  P and T(P  T)

9. Pressure Gauge Pressure Gauge Today’s temp: 35°F

10. Pressure Gauge Pressure Gauge Today’s temp: 85°F

11. Back to Pressure… Collisions between gas molecules and container exerts a force on container wall  More collisions and more energetic collisions = greater force = higher pressure Kinetic molecular theory gives conceptual framework for understanding the behavior of gases  P and n(P  n)  P and T(P  T)  V and T (V  1/T)  P and V(P  1/V)

12. Volume of balloon at room temperature Volume of balloon at 5°C

13. The Gas Laws Boyle’s Charles’ Avogadro’s Ideal Gas Law

14. Using the Gas Laws If you know 3 variables, solve for the fourth If some properties are constant, trends in one property can predict another STP (“Standard Temperature and Pressure”)  T= 273 K  P= 1 atm Strategy: Take note of the variables you know, find the appropriate equation, then “plug and chug” (or just remember PV=nRT and derive the appropriate equation every time)

15. Examples 1. A gas has a volume of 3L at 2 atm. What is its volume at 4 atm? 2. A gas has a volume of 4.1 L at 127  C. What is its volume at 227  ?

16. Examples 3. What volume does 7.4 grams of ethane (C 2 H 2 ) occupy at standard temperature and pressure? 4. The propane tank of a camping stove contains 3,000g of liquid C 3 H 8. How large a container would be needed to hold the same amount of propane as a gas at 25  C and 2250mmHg?