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Chapter 11 Behavior of Gases

Chapter 11 Behavior of Gases. Objectives. 11.1 Model the effects of changing the number of particles, mass, temperature, pressure, and volume on a gas using kinetic theory 11.1 Measure atmospheric pressure 11.1 Demonstrate the ability to use the factor label method to convert pressure units.

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Chapter 11 Behavior of Gases

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  1. Chapter 11 Behavior of Gases

  2. Objectives • 11.1Model the effects of changing the number of particles, mass, temperature, pressure, and volume on a gas using kinetic theory • 11.1 Measure atmospheric pressure • 11.1 Demonstrate the ability to use the factor label method to convert pressure units

  3. Objectives • 11.2Analyze data that relate temperature, pressure, and volume of gas • 11.2 Model Boyle's law and Charle'slaw using kinetic theory • 11.2 Predict the effect of changes in pressure and temperature on the volume of a gas • 11.2 Relate how volumes of gases react in terms of the kinetic theory of matter

  4. Characteristics of Gases • Unlike liquids and solids, they • Expand to fill their containers. • Are highly compressible. • Have extremely low densities.

  5. Main Tenets of Kinetic-Molecular Theory Gases consist of large numbers of molecules that are in continuous, random motion.

  6. Main Tenets of Kinetic-Molecular Theory • The combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained. • Attractive and repulsive forces between gas molecules are negligible.

  7. Main Tenets of Kinetic-Molecular Theory Energy can be transferred between molecules during collisions, but the average kinetic energy of the molecules does not change with time, as long as the temperature of the gas remains constant.

  8. Main Tenets of Kinetic-Molecular Theory The average kinetic energy of the molecules is proportional to the absolute temperature.

  9. Deviations from Ideal Behavior The assumptions made in the kinetic-molecular model break down at high pressure and/or low temperature.

  10. F A P = Pressure • Pressure is the amount of force applied to an area. • Atmospheric pressure is the weight of air per unit of area.

  11. Pressure • Takes into account • Number of collisions per second • Amount of force the collision imparts to surface • Number of particles goes up = More collisions • As temperature goes up = Collisions increase and hit with more force

  12. Units of Pressure • mm Hg or torr • These units are literally the difference in the heights measured in mm (h) of two connected columns of mercury. • Atmosphere • 1.00 atm = 760 torr

  13. Other units of Pressure • PSI • Pounds per square inch • Commonly used in America • Used by most American weather forecasters • Atm • Atmospheres • 1.0 Atmosphere is equivalent to 760mm Hg or 101,325 Pascals or 14.7 PSI • Based off atmosphere weight

  14. Weight of the Atmosphere • Varies on a regular basis • High and Low pressure • Varies by location • Mountains have less air on top • less pressure = lower BP • Some people claim that they can detect these changes… myth or fact?

  15. Manometer Used to measure the difference in pressure between atmospheric pressure and that of a gas in a vessel.  As drawn, the atmosphere has a low pressure

  16. Convert • A) 59.8 in Hg to PSI • B) 7.35 PSI to mm Hg • C) 1140 mm Hg to kPa • D) 28 in Hg to Atm • E) 32 PSI to mm Hg • Equivalent Measures • 760 mmHg • 1.0 inch = 25.4 mm • 1.0 Atm • 14.7 PSI • 101.325 kPa

  17. General Rules Concerning Gases • As pressure goes up, volume goes down • As temperature goes up, volume goes up • As number of molecules increases, pressure goes up

  18. Chapter 11.2 • The Math Part

  19. Boyle’s Law Pressure and Volume are Inversely Proportional Assuming Constant Temperature P1V1 = P2V2

  20. Boyle’s Law • Double the Volume = Half the pressure • Half the Volume = Double the pressure • Assuming Constant Temperature

  21. Calculation • A certain gas has a volume of 4 L and a pressure of 1.0 atmosphere. If the volume of the gas decreases to 1 L, what is the new pressure that the gas exerts? • Random Fact: Many tapes utilize boyle’s law to help maintain their stickiness. As a tape is lifted, tiny bubbles increase in size and the pressure drops creating a vacuum

  22. Boyle’s Law Examples • Pertinent to our breathing. • How big of a pressure difference do you think our chest cavities can create? • What is the volume of your lungs when fully inhaled? • What is the volume of your lungs when fully exhaled? • Explain how a vacuum works

  23. Boyle’s Law Examples • Relevant to weather balloons • As the balloon rises, the pressure on the outside decreases, the balloon expands so that the pressure inside is the same as the outside • At approximately 15 km, the altitude is 1/10 of sea level, so the balloon will expand to a volume of 10x its original • Balloons pop at certain height

  24. Boyle’s Law Examples • Relevant to deep sea divers • 10 m of water depth is equal approximately to the atmosphere • At high pressure, gas is forced into the blood stream easier. Later on, when you return, the gas in the vessels and arteries expands, called the Benz

  25. Boyle’s Law Examples • Relevant to medicine • Hyperbaric chambers: High pressure container designed to help the body heal • Used by sports teams, used to treat premature babies, used for patients after heart attacks • Some Young Earth Creationists speculate that before the flood, pressure was larger allowing for large animals to exist • Used for bigger plants too (super green house)

  26. V T = k • i.e., Charles’s Law • The volume of a fixed amount of gas is proportional to its absolute temperature. A plot of V versus T will be a straight line.

  27. Calculation • A certain gas has a volume of 500 mL at a temperature of 20 C. What is the volume of the gas at – 20 C? • Need to use Kelvin, how you end up with negative volumes • V1/T1 = V2/T2

  28. Charle’s Law Examples • Hot Air Balloons • Increasing the temperature results in a larger volume of gas • Results in a smaller density

  29. V = kn • Mathematically, this means Avogadro’s Law • The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas.

  30. Standard Atmospheric Temperature and Pressure • Called STP • Basis of comparison • 0 Celsius and 1 atmosphere • Doesn’t matter the gas, 1 mol of any type of gas occupies 22.4 Liters of space at STP • Will discuss the mol later in greater detail

  31. Combined Gas Law • PV/T = PV/T • If an original gas has a volume of 2.0 L, and the pressure is doubled and the Temperature is doubled, what is the new Volume? • Later on will use PV = nRT • R is a constant (based off pressure used) • n is mols of gas

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