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Gases

Gases. Themes: Structure Meets Function; Equilibrium. Kinetic Molecular Theory. All gases behave the same way if the following are true : A gas moves in straight line motion Gas molecules have negligible volume Collisions between gas particles are elastic

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Gases

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  1. Gases Themes: Structure Meets Function; Equilibrium

  2. Kinetic Molecular Theory • All gases behave the same way if the following are true: • A gas moves in straight line motion • Gas molecules have negligible volume • Collisions between gas particles are elastic • Gas molecules don’t attract or repel each other. • You are not at absolute zero!

  3. When do real gases behave ideally? • At standard pressure and temperature. • Pressure= 1 atm • Temperature= 0 °C • At extremely high pressures and extremely low temperatures, gases will not be “ideal”

  4. What is pressure?

  5. How can we measure pressure? • Atmospheres; mmHg; kPa • Manometer measures mmHg

  6. Combined gas law • Use when moles or g of gas is unknown and not a part of the problem! And when you are looking at change in pressure or volume!

  7. Practice • You are riding your bike on a hot day. Your tires can only withstand pressure of 760 mmHg. You pump your tires up to 750 mmHg at 23 °C. You ride for ten minutes and the temperature of your bike tires heats up to 50 °C. If the volume of the tires is held constant are you in danger of your tires popping? Use math to explain why or why not!

  8. Ideal Gas Law • If you want to include moles (or grams) of gas, you must include n and use the ideal gas law. • Use when you are looking to solve for 1 variable! • In this case, the units must match your R value!

  9. Practice • If you have a 10L canister containing 10 g of N2 gas at 23°C, what would the pressure in the canister be?

  10. Partial Pressures • Dalton’s law of partial pressures, says that the total pressure in a container is the sum of each of the partial pressures. • For pressure of an individual gas by: • Multiplying the portion by the total pressure!

  11. Practice • Easy: Air is 72% N2, 21% O2 and the remainder H2O vapor. What is the partial pressure of O2 in air on a day where the pressure is 765 mmHg? • Hard: The mixture in a gas cylinder is 0.5 moles N2, 0.3 moles CH4, and 0.1 mole O2. What is the partial pressure of methane if the container is compressed to 40 mmHg?

  12. Diffusion • Gases tend to move to areas of lesser concentration. • If a mixture of gases is moving, the rate of diffusion is inversely proportional to their masses. (what does this mean?!?)

  13. Practice • It takes 354 s for Xe to effuse (diffuse through a small hole). How long would it take nitrogen gas to effuse through the same hole?

  14. On your own practice • Practice the assigned gas law problems. In a class later this week, you will be assigned a group and have to complete 3 challenging gas law problems as a group (for a grade!)

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