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December 9, 2009

December 9, 2009. 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

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December 9, 2009

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  1. December 9, 2009 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.)

  2. 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

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

  4. Gas Diffusion

  5. Gas Effusion • Graham’s Law of Effusion

  6. Graham’s Law Example A sample of ethane, C2H6, 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.

  7. 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)

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

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

  10. 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)

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

  12. The Gas Laws • Boyle’s • Charles’ • Avogadro’s Ideal Gas Law

  13. 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)

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

  15. Examples • What volume does 7.4 grams of ethane (C2H2) occupy at standard temperature and pressure? • The propane tank of a camping stove contains 3,000g of liquid C3H8. How large a container would be needed to hold the same amount of propane as a gas at 25C and 2250mmHg?

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