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# Lecture 14.4- Diffusion (PREP)

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Section 14.4 Lecture for Prep chemistry

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• Three gases are combined in container T. The pressure that each gas exerts is independent of the pressure exerted by the other two gases. The pressure in container T is the sum of the pressures in containers A, B, and C. Interpreting Diagrams What is the relationship between the number of particles in containers A and C and the partial pressures of the gases in A and C?
• This climber is using a tank of compressed gas to supplement the supply of oxygen available at high altitudes.
• Firefighters carry tanks of compressed air. The tanks contain from 19.5% to 23.5% oxygen by volume.
• The diffusion of one substance through another is a relatively slow process. a) Bromine vapor is diffusing upward through the air in a graduated cylinder. b) After several hours, bromine vapors are near the top of the cylinder. Predicting What will happen as the bromine continues to diffuse?
• The diffusion of one substance through another is a relatively slow process. a) Bromine vapor is diffusing upward through the air in a graduated cylinder. b) After several hours, bromine vapors are near the top of the cylinder. Predicting What will happen as the bromine continues to diffuse?
• The character balloons used in parades are filled with helium gas so that they will float.
• ### Lecture 14.4- Diffusion (PREP)

1. 1. Chemistry 14.4 Bellwork- Ideal Gas Law How many moles of oxygen gas are in a balloon at 25  C with an internal pressure of 1.1 atm and a volume of 1500ml? P 1 V 1 P 2 V 2 PV = nRT T 1 T 2 R= 8.31 L  kPa / K  mol R= 0.0821 L  atm / K  mol =
2. 2. <ul><li>A list of gear for an expedition to Mount Everest includes climbing equipment, ski goggles, a down parka with a hood, and most importantly compressed-gas cylinders of oxygen. You will find out why a supply of oxygen is essential at higher altitudes. </li></ul>
3. 3. <ul><ul><ul><li>The contribution each gas in a mixture makes to the total pressure is called the partial pressure exerted by that gas. </li></ul></ul></ul>
4. 4. <ul><ul><li>Dalton’s law of partial pressures- In a mixture of gases, the total pressure is the sum of the partial pressures of the gases. </li></ul></ul>
5. 5. <ul><ul><ul><li>Three gases are combined in container T. </li></ul></ul></ul><ul><ul><ul><li>100 kPa + 250kPa + 200kPa = 550kPa </li></ul></ul></ul>
6. 6. <ul><ul><ul><li>The partial pressure of oxygen must be 10.67 kPa or higher to support respiration in humans. The climber below needs an oxygen mask and a cylinder of compressed oxygen to survive. </li></ul></ul></ul>Atmospheric pressure at the top of the world (29,000ft above sea level) = 30kPa
7. 7. 14.6
8. 8. 14.6
9. 9. 14.6
10. 10. 14.6
11. 11. for Sample Problem 14.6
12. 12. <ul><ul><ul><li>Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout. </li></ul></ul></ul>
13. 13. Graham’s Law <ul><ul><ul><li>Bromine vapor is diffusing upward through the air in a graduated cylinder. </li></ul></ul></ul>
14. 14. Graham’s Law <ul><ul><ul><li>After several hours, the bromine has diffused almost to the top of the cylinder. </li></ul></ul></ul>
15. 15. <ul><ul><ul><ul><li>Gases of lower molar mass diffuse faster than gases of higher molar mass. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>AT THE SAME TEMPERATURE! </li></ul></ul></ul></ul><ul><ul><ul><ul><li>HEAVIER = SLOWER </li></ul></ul></ul></ul>
16. 16. <ul><ul><li>A helium filled balloon will deflate sooner than an air-filled balloon. </li></ul></ul><ul><ul><ul><li>Helium atoms are less massive than oxygen or nitrogen molecules. So the molecules in air move more slowly than helium atoms with the same kinetic energy. </li></ul></ul></ul>