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Introductory Chemistry , 2 nd Edition Nivaldo Tro

Introductory Chemistry , 2 nd Edition Nivaldo Tro. Chapter 11 Gases. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA. 2006, Prentice Hall. Gases Pushing. gas molecules are constantly in motion as they move and strike a surface, they push on that surface push = force

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Introductory Chemistry , 2 nd Edition Nivaldo Tro

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  1. Introductory Chemistry, 2nd EditionNivaldo Tro Chapter 11 Gases Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA 2006, Prentice Hall

  2. Gases Pushing • gas molecules are constantly in motion • as they move and strike a surface, they push on that surface • push = force • if we could measure the total amount of force exerted by gas molecules hitting the entire surface at any one instant, we would know the pressure the gas is exerting • pressure = force per unit area Tro's Introductory Chemistry, Chapter

  3. The Effect of Gas Pressure • the pressure exerted by a gas can cause some amazing and startling effects • whenever there is a pressure difference, a gas will flow from area of high pressure to low pressure • the bigger the difference in pressure, the stronger the flow of the gas • if there is something in the gas’ path, the gas will try to push it along as the gas flows Tro's Introductory Chemistry, Chapter

  4. Soda Straws & Gas Pressure The pressure of the air inside the straw is the same as the pressure of the air outside the straw – so liquid levels is the same on both sides. The pressure of the air inside the straw is lower than the pressure of the air outside the straw – so liquid is pushed up the straw by the outside air. Tro's Introductory Chemistry, Chapter

  5. Air Pressure • the atmosphere exerts a pressure on everything it contacts • on average 14.7 psi • the atmosphere goes up about 370 miles, but 80% is in the first 10 miles from the earth’s surface • this is the same pressure that a column of water would exert if it were about 10.3 m high Tro's Introductory Chemistry, Chapter

  6. Properties of Gases • expand to completely fill their container • take the shape of their container • low density • much less than solid or liquid state • compressible • mixtures of gases are always homogeneous • fluid Tro's Introductory Chemistry, Chapter

  7. Kinetic Molecular Theory • the particles of the gas, (either atoms or molecules), are constantly moving • the attraction between particles is negligible • when the moving particles hit another particle or the container, they do not stick; but they bounce off and continue moving in another direction • like billiard balls Tro's Introductory Chemistry, Chapter

  8. Kinetic Molecular Theory • there is a lot of empty space between the particles • compared to the size of the particles • the average kinetic energy of the particles is directly proportional to the Kelvin temperature • as you raise the temperature of the gas, the average speed of the particles increases • but don’t be fooled into thinking all the particles are moving at the same speed!! Tro's Introductory Chemistry, Chapter

  9. Kinetic Molecular Theory Tro's Introductory Chemistry, Chapter

  10. Gas Properties Explained • Gases have indefinite shape and volume because the freedom of the molecules allows them to move and fill the container they’re in • Gases are compressible and have low density because of the large spaces between the molecules Tro's Introductory Chemistry, Chapter

  11. Properties – Indefinite Shape and Indefinite Volume Because the gas molecules have enough kinetic energy to overcome attractions, they keep moving around and spreading out until they fill the container As a result, gases take the shape and the volume of the container they are in. Tro's Introductory Chemistry, Chapter

  12. Properties - Compressibility Because there is a lot of unoccupied space in the structure of a gas, the gas molecules can be squeezed closer together Tro's Introductory Chemistry, Chapter

  13. Properties – Low Density Because there is a lot of unoccupied space in the structure of a gas, gases have low density Tro's Introductory Chemistry, Chapter

  14. The Pressure of a Gas • result of the constant movement of the gas molecules and their collisions with the surfaces around them • the pressure of a gas depends on several factors • number of gas particles in a given volume • volume of the container • average speed of the gas particles Tro's Introductory Chemistry, Chapter

  15. Measuring Air Pressure • use a barometer • column of mercury supported by air pressure • force of the air on the surface of the mercury balanced by the pull of gravity on the column of mercury gravity Tro's Introductory Chemistry, Chapter

  16. Atmospheric Pressure & Altitude • the higher up in the atmosphere you go, the lower the atmospheric pressure is around you • at the surface the atmospheric pressure is 14.7 psi, but at 10,000 ft is is only 10.0 psi • rapid changes in atmospheric pressure may cause your ears to “pop” due to an imbalance in pressure on either side of your ear drum Tro's Introductory Chemistry, Chapter

  17. Pressure Imbalance in Ear If there is a difference in pressure across the eardrum membrane, the membrane will be pushed out – what we commonly call a “popped eardrum.” Tro's Introductory Chemistry, Chapter

  18. Common Units of Pressure Tro's Introductory Chemistry, Chapter

  19. Example 11.1:Converting Between Pressure Units

  20. Example: A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury? Tro's Introductory Chemistry, Chapter

  21. Write down the given quantity and its units. Given: 125 psi Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury? Tro's Introductory Chemistry, Chapter

  22. Write down the quantity to find and/or its units. Find: ? mmHg Information Given: 125 psi Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury? Tro's Introductory Chemistry, Chapter

  23. Collect Needed Conversion Factors: 14.7 psi = 760 mmHg Information Given: 125 psi Find: ? mmHg Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury? Tro's Introductory Chemistry, Chapter

  24. Write a Solution Map for converting the units : Information Given: 125 psi Find: ? mmHg CF: 14.7 psi = 760 mmHg Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury? psi mmHg Tro's Introductory Chemistry, Chapter

  25. Apply the Solution Map: Information Given: 125 psi Find: ? mmHg CF: 14.7 psi = 760 mmHg SM: psi → mmHg Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury? = 6.46259 x 103 mmHg • Sig. Figs. & Round: = 6.46 x 103 mmHg the 760 is an exact number and does not effect the significant figures Tro's Introductory Chemistry, Chapter

  26. Check the Solution: Information Given: 125 psi Find: ? mmHg CF: 14.7 psi = 760 mmHg SM: psi → mmHg Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury? 125 psi = 6.46 x 103 mmHg The units of the answer, mmHg, are correct. The magnitude of the answer makes sense since mmHg are smaller than psi. Tro's Introductory Chemistry, Chapter

  27. Boyle’s Law • pressure of a gas is inversely proportional to its volume • constant T and amount of gas • graph P vs V is curve • graph P vs 1/V is straight line • as P increases, V decreases by the same factor • P x V = constant • P1 x V1 = P2 x V2 Tro's Introductory Chemistry, Chapter

  28. Boyle’s Experiment • added Hg to a J-tube with air trapped inside • used length of air column as a measure of volume Tro's Introductory Chemistry, Chapter

  29. Tro's Introductory Chemistry, Chapter

  30. Tro's Introductory Chemistry, Chapter

  31. Boyle’s Experiment, P x V Tro's Introductory Chemistry, Chapter

  32. When you double the pressure on a gas, the volume is cut in half, (as long as the temperature and amount of gas do not change) Tro's Introductory Chemistry, Chapter

  33. Boyle’s Law & Breathing • inhale • diaphragm & rib muscles contract • chest cavity expands - volume increase • pressure inside lungs drops below air pressure • air flows into lung to equilibrate pressure • gases move from hi pressure to low • exhale • diaphragm & rib muscles relax • chest cavity volume decreases • pressure inside lungs rises above air pressure • air flows out of lung to equilibrate pressure • normal healthy person can generate a lung pressure of 1.06 atm Tro's Introductory Chemistry, Chapter

  34. Boyle’s Law and Diving • since water is denser than air, for each 10 m you dive below the surface the pressure on your lungs increases 1 atm • at 20 m the total pressure is 3 atm • if your tank contained air at 1 atm pressure you would not be able to inhale it into your lungs Tro's Introductory Chemistry, Chapter

  35. Boyle’s Law and Diving • scuba tanks have a regulator so that the air in the tank is delivered at the same pressure as the water surrounding you • if a diver holds her breath and rises quickly, so that the outside pressure drops to 1 atm; according to Boyle’s Law, what should happen to the volume of air in the lungs? Tro's Introductory Chemistry, Chapter

  36. Which Way Would Air Flow? Tro's Introductory Chemistry, Chapter

  37. Is this possible at a depth of 20 m? Tro's Introductory Chemistry, Chapter

  38. Example 11.2:Boyle’s Law

  39. Example: A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm? Tro's Introductory Chemistry, Chapter

  40. Write down the given quantity and its units. Given: P1 = 4.0 atm V1 = 6.0 L P2 = 1.0 atm Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm? Tro's Introductory Chemistry, Chapter

  41. Write down the quantity to find and/or its units. Find: V2, L Information Given: P1 = 4.0 atm V1 = 6.0 L P2 = 1.0 atm Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm? Tro's Introductory Chemistry, Chapter

  42. Collect Needed Equation: The relationship between pressure and volume is Boyle’s Law Information Given: P1 = 4.0 atm V1 = 6.0 L P2 = 1.0 atm Find: V2 = ? L Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm? Tro's Introductory Chemistry, Chapter

  43. Write a Solution Map: Information Given: P1 = 4.0 atm V1 = 6.0 L P2 = 1.0 atm Find: V2 = ? L Eq’n: P1 ∙ V1 = P2 ∙ V2 Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm? P1, V1, P2 V2 when using this equation, the units of P1 and P2 must be the same, or you will have to convert one to the other for the same reason, the units of V2 must be L to match the unit of V1 Tro's Introductory Chemistry, Chapter

  44. Apply the Solution Map: Information Given: P1 = 4.0 atm V1 = 6.0 L P2 = 1.0 atm Find: V2 = ? L Eq’n: P1 ∙ V1 = P2 ∙ V2 SM: P1, V1, P2 → V2 Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm? • Sig. Figs. & Round: Tro's Introductory Chemistry, Chapter

  45. Check the Solution: Information Given: P1 = 4.0 atm V1 = 6.0 L P2 = 1.0 atm Find: V2 = ? L Eq’n: P1 ∙ V1 = P2 ∙ V2 SM: P1, V1, P2 → V2 Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm? V2 = 24 L The units of the answer, L, are correct. The magnitude of the answer makes sense - since the pressure is decreasing the volume should be increasing. Tro's Introductory Chemistry, Chapter

  46. Temperature Scales 100°C 373 K 212°F 671 R BP Water 0°C 273 K 32°F 459 R MP Ice -38.9°C 234.1 K -38°F 421 R BP Mercury -183°C 90 K -297°F 162 R BP Oxygen BP Helium -269°C 4 K -452°F 7 R -273°C 0 K -459 °F 0 R Absolute Zero Celsius Kelvin Fahrenheit Rankine

  47. Standard Conditions • Common reference points for comparing • standard pressure = 1.00 atm • standard temperature = 0°C • 273 K • STP Tro's Introductory Chemistry, Chapter

  48. Volume and Temperature • In a rigid container, raising the temperature increases the pressure • For a cylinder with a piston, the pressure outside and inside stay the same • To keep the pressure from rising, the piston moves out increasing the volume of the cylinder • as volume increases, pressure decreases Tro's Introductory Chemistry, Chapter

  49. As a gas is heated, it expands. This causes the density of the gas to decrease. Because the hot air in the balloon is less dense than the surrounding air, it rises. Volume and Temperature Tro's Introductory Chemistry, Chapter

  50. Charles’ Law • volume is directly proportional to temperature • constant P and amount of gas • graph of V vs T is straight line • as T increases, V also increases • Kelvin T = Celsius T + 273 • V = constant x T • if T measured in Kelvin Tro's Introductory Chemistry, Chapter

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