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# Lecture 14.1 & 14.2- Gas Laws & KMT

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Section 14.1 & 14.2 lecture for Honors & Prep Chemistry

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• A crash dummy can be used to test the effectiveness of an air bag. Because gases can be compressed, the air bag absorbs some of the energy from the impact of a collision. Air bags work best when combined with seat belts.
• There are only a few nitrogen and oxygen molecules in this model of air. At room temperature, the distance between molecules in a container of air at standard pressure is about 10 times the diameter of a molecule.
• The volume of this air-filled raft is much larger than its volume before it was inflated. Using a pump to force air into a raft increases the pressure of the air inside the raft. The increased pressure causes the raft to inflate to its intended size.
• When a gas is pumped into a closed rigid container, the pressure increases as more particles are added. If the number of particles is doubled, the pressure will double. Predicting What would happen to the pressure in the container if the number of particles were tripled? If the number of particles were cut in half?
• The pressure of the gas inside a new can of spray paint is greater than the air pressure outside the can. When gas rushes though an opening in the top of the can, it propels, or forces, paint out of the can. As the can is used, the pressure of the propellant decreases. Relating Cause and Effect What happens when the pressure of the propellant equals the air pressure outside the can?
• A piston can be used to force a gas in a cylinder into a smaller volume. When the volume is decreased, the pressure the gas exerts is increased. Interpreting Diagrams What happens to the gas pressure when the volume is reduced from 1 L to 0.5 L?
• An increase in temperature causes an increase in the pressure of an enclosed gas. The container can explode if there is too great an increase in the pressure.
• An increase in temperature causes an increase in the pressure of an enclosed gas. The container can explode if there is too great an increase in the pressure.
• In a pressure cooker, food cooks faster than in an ordinary pot with a lid.
• When a gas is heated at constant volume, the pressure increases. Interpreting Diagrams How can you tell from the drawings that there is a fixed amount of gas in the cylinders?
• When the gas in the blue balloon is cooled at constant pressure, the volume of the gas decreases. When the gas is heated at constant pressure, the volume increases. Calculating What is the ratio of volume to temperature for each set of conditions? Round your answer to two significant figures .
• ### Lecture 14.1 & 14.2- Gas Laws & KMT

1. 1. Properties of Gases <ul><li>In organized soccer, a ball that is properly inflated will rebound faster and travel farther than a ball that is under-inflated. If the pressure is too high, the ball may burst when it is kicked. You will study variables that affect the pressure of a gas. </li></ul>What factors affect the pressure of the air inside the ball? What causes the pressure in the ball?
2. 2. <ul><ul><ul><li>Compressibility is a measure of how much the volume of matter decreases under pressure. </li></ul></ul></ul><ul><ul><ul><li>When a person collides with an inflated airbag, the compression of the gas absorbs the energy of the impact. </li></ul></ul></ul>
3. 3. <ul><ul><ul><li>Gases are easily compressed because there is a lot of space between the particles in a gas. </li></ul></ul></ul><ul><ul><ul><ul><ul><li>The distance between particles in a gas is much greater than the distance between particles in a liquid or solid. </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Under pressure, the particles in a gas are forced closer together. </li></ul></ul></ul></ul></ul>
4. 4. <ul><ul><ul><li>At room temperature, the distance between particles in an enclosed gas is about 10 times the diameter of a particle. </li></ul></ul></ul>
5. 5. <ul><ul><li>The amount of gas, volume, and temperature are factors that affect gas pressure. </li></ul></ul><ul><ul><li>The relationships between these factors are described by GAS LAWS. </li></ul></ul>
6. 6. <ul><ul><ul><li>The four variables used to describe a gas and their common units are </li></ul></ul></ul><ul><ul><ul><ul><li>pressure ( P ) in kilopascals or atm </li></ul></ul></ul></ul><ul><ul><ul><ul><li>volume ( V ) in liters </li></ul></ul></ul></ul><ul><ul><ul><ul><li>temperature ( T ) in kelvins </li></ul></ul></ul></ul><ul><ul><ul><ul><li>the number of moles ( n ). </li></ul></ul></ul></ul>
7. 7. <ul><ul><li>Avogadro’s Law- n  P  </li></ul></ul><ul><ul><ul><li>You can use kinetic theory to predict and explain how gases will respond to a change of conditions. </li></ul></ul></ul><ul><ul><ul><li>If you inflate an air raft, </li></ul></ul></ul><ul><ul><ul><li>for example, the pressure </li></ul></ul></ul><ul><ul><ul><li>inside the raft will increase. </li></ul></ul></ul>
8. 8. <ul><ul><ul><li>Collisions of particles create pressure. </li></ul></ul></ul><ul><ul><ul><li>Increasing the number of gas particles increases the number of collisions, which is why the gas pressure increases. </li></ul></ul></ul><ul><ul><ul><li>Avogadro’s Law- n  P  </li></ul></ul></ul><ul><ul><ul><li>directly proportional </li></ul></ul></ul>
9. 9. <ul><ul><ul><li>If the gas pressure increases until it exceeds the strength of an enclosed, rigid container, the container will burst. </li></ul></ul></ul>
10. 10. Not for the faint at heart…
11. 11. <ul><li>Aerosol Spray Paint </li></ul><ul><li>Gas flows from a region of higher pressure to a region of lower pressure </li></ul>
12. 12. <ul><ul><li>Boyle’s law - V  P  or V  P  </li></ul></ul><ul><ul><ul><li>You can raise the pressure exerted by a contained gas by reducing its volume. </li></ul></ul></ul><ul><ul><ul><li>The more a gas is compressed, the greater the pressure of the gas. </li></ul></ul></ul>
13. 13. <ul><ul><li>When volume decreases, particles do not have to travel as far before they hit the side of the container. </li></ul></ul>
14. 14. <ul><ul><li>This causes more collisions and therefore more pressure. </li></ul></ul>
15. 15. <ul><ul><li>Boyle’s Law- V  P  </li></ul></ul><ul><ul><li>Indirect relationship </li></ul></ul>
16. 16. <ul><ul><ul><li>When the volume of the container is halved, the pressure the gas exerts is doubled. </li></ul></ul></ul>
17. 17. <ul><ul><li>Gay-Lussac’s Law- T  P  </li></ul></ul><ul><ul><ul><li>An increase in the temperature of an enclosed gas causes an increase in its pressure. </li></ul></ul></ul><ul><ul><ul><li>As a gas is heated, the average kinetic energy of the particles in the gas increases. </li></ul></ul></ul>
18. 18. <ul><ul><li>Gay-Lussac’s Law- T  P  </li></ul></ul><ul><ul><ul><li>An increase in the temperature of an enclosed gas causes an increase in its pressure. </li></ul></ul></ul><ul><ul><ul><li>Faster-moving particles strike the walls of their container more often and with more energy. </li></ul></ul></ul>
19. 19. <ul><ul><li>Gay-Lussac’s Law - T  P  </li></ul></ul><ul><ul><ul><li>An increase in the temperature of an enclosed gas causes an increase in its pressure. </li></ul></ul></ul><ul><ul><ul><li>Pressure = force/area </li></ul></ul></ul><ul><ul><ul><li>So more force (harder & more frequent collisions) makes more pressure. </li></ul></ul></ul>
20. 20. <ul><ul><ul><li>When the Kelvin temperature of the enclosed gas doubles, the pressure of the enclosed gas doubles. </li></ul></ul></ul>
21. 21. <ul><ul><ul><li>Gay-Lussac’s Law - T  P  </li></ul></ul></ul><ul><ul><ul><li>Directly proportional </li></ul></ul></ul>
22. 22. <ul><li>Gay-Lussac’s Law: T  P  </li></ul><ul><ul><ul><ul><li>As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant. </li></ul></ul></ul></ul>
23. 23. <ul><li>A pressure cooker demonstrates Gay-Lussac’s Law. </li></ul>
24. 24. <ul><li>Charles’ Law- T  V  </li></ul><ul><li>When a gas is heated at constant pressure , the volume increases. </li></ul>
25. 25. <ul><li>Charles’ Law- T  V  </li></ul><ul><ul><ul><ul><li>As the temperature of an enclosed gas increases, the volume increases, if the pressure is constant. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>T  ,V  </li></ul></ul></ul></ul>
26. 26. <ul><li>As the temperature of the water increases, the volume of the balloon increases. </li></ul>
27. 27. <ul><li>The KMT explains Gay-Lussac’s Law- </li></ul><ul><li>as temperature increases particles move faster, so they will collide more often and harder, increasing the pressure. </li></ul><ul><li>In order to maintain constant pressure, the volume will need to increase! </li></ul><ul><li>Charles’ Law- T  V  </li></ul><ul><li>if pressure is constant </li></ul>
28. 28. <ul><li>The combined gas law describes the relationship among the pressure, temperature, and volume of an enclosed gas. </li></ul>
29. 29. <ul><ul><li>The combined gas law allows you to do calculations for situations in which only the amount of gas is constant. </li></ul></ul>
30. 30. <ul><ul><li>1. Compared to liquids and solids, gases are easily compressed because the particles in a gas </li></ul></ul><ul><ul><ul><li>attract each other. </li></ul></ul></ul><ul><ul><ul><li>are spaced relatively far apart. </li></ul></ul></ul><ul><ul><ul><li>are very small. </li></ul></ul></ul><ul><ul><ul><li>repel each other. </li></ul></ul></ul>14.1 Section Quiz.
31. 31. <ul><ul><li>2. Gas pressure is affected by </li></ul></ul><ul><ul><ul><li>temperature, volume, and the amount of the gas. </li></ul></ul></ul><ul><ul><ul><li>temperature, volume, and the molar mass of the gas. </li></ul></ul></ul><ul><ul><ul><li>phase diagram, volume, and the size of the container. </li></ul></ul></ul><ul><ul><ul><li>temperature, phase diagram, and the mass of the gas container. </li></ul></ul></ul>14.1 Section Quiz.
32. 32. <ul><ul><li>3. For gases, the SI units for volume ( V ), pressure ( P ), and temperature ( T ) are, respectively, </li></ul></ul><ul><ul><ul><li>liters, kilopascals, and °C. </li></ul></ul></ul><ul><ul><ul><li>liters, kilopascals, and kelvins. </li></ul></ul></ul><ul><ul><ul><li>cm 3 , kilopascals, and kelvins. </li></ul></ul></ul><ul><ul><ul><li>liters, atmospheres, and °C. </li></ul></ul></ul>14.1 Section Quiz.
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