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Gas Laws

Gas Laws. Chapter 13. Elements that exist as gases at 25 0 C and 1 atmosphere. Observed GAS physical properties. Gases have mass Gases can compress (springy) Gases FILL containers completely Gases diffuse through each other (bad smells). Gases exert pressure

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Gas Laws

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  1. Gas Laws Chapter 13

  2. Elements that exist as gases at 250C and 1 atmosphere

  3. Observed GAS physical properties • Gases have mass • Gases can compress (springy) • Gases FILL containers completely • Gases diffuse through each other (bad smells). • Gases exert pressure • Pressure depends on temperature. • These properties led to the Kinetic molecular theory (KMT)

  4. The KMT says that gases….…. • Consist of small particles having mass • Distance between particles large (particle size close to 0) • Particles always move at random speeds in random directions. • Perfectly elastic collisions (no energy lost) • Average KE of particles proportional to T. • Forces between particles is zero.

  5. Measuring Gases • n, moles of gas = Mass___ Molar Mass • Volume in L . (1000cm3 = 1L) • Temperature, K . (K = °C + 273.15) • Pressure , Pascals (Pa)

  6. 10 miles 0.2 atm 4 miles 0.5 atm Sea level 1 atm

  7. Atmospheric Pressure • Above every square inch of the earth’s surface is about 15 Lbs of air. It is like being at the bottom of a gas sea. • Higher up, ex.Denver there is ___ pressure • Think of aircraft altimeters, • Ears, Cooking, weather,Sports. • Barometer measures atmospheric pressure.

  8. Force Area Barometer Pressure = Units of Pressure 1 pascal (Pa) = 1 N/m2 1 atm =760mmHg=760 torr 1 atm = 101,325 Pa

  9. Closed End Open ended

  10. Using a manometer • Manometer measures pressure differences. We are only using open-ended ones in the problems (P13) • Pressure in connected container (mmHg) = height difference + atmospheric pressure. The height diff. is (+) when the open end is higher than the closed end. The height diff. is (-) when the open end is ___erthan the closed end. ALWAYS DRAW A PICTURE FOR MANOMETER PROBLEMS!!!!!!!!

  11. You must be able to convert between units of pressure…… • Use the following conversion factors: • 1atm = 101,325 Pa • 1atm = 760mm Hg • 1 atm = 14.70 Lb/in2 • 1 bar = 100,000 Pa • Let’s do some problems on the board…..

  12. How many mmHg is 3.5atm? • Convert 35psi to atm. • How many Pa is 6.4 atm? • Convert 5000Pa to atm. • The next ones must got to atm first and then to the desired unit • How many psi is 50.0 Pa? • How many mmHg is 200,000Pa? • How many psi is 2500Pa?

  13. Section 13.3 • What happens the volume of a gas when the pressure increases? • This is described by Boyles Law : • “At a constant temperature, the volume of a gas is inversely proportional to the pressure” • This is expressed by P1V1 = P2V2 P is pressure, V is Volume (L), 1 means initial, 2 means final

  14. Some examples of Boyles Law • Bag of chips taken from sea level to Denver. What happens the bag? • Take a helium balloon from top of Sears tower to street level. What happens? • What happens your eardrum as you go up in a plane?

  15. Charles Law • “At a constant pressure, the volume of a gas is proportional to the temperature” • V1T2 = V2T1 • Examples: • Hot air balloon • Internal combustion engine • Explosion • What would happen if you took a balloon and put it in the freezer?

  16. Pop Test • Please take out FIVE blank sheets of paper and your calculators. • Solve the following 20 problems, showing all work using the G.U.E.S.S. method. • 1) Find the new Volume of a hedgehog travelling at 0.5m/s with a body temperature of 5K going north. The mass of the hedgehog is 1.5kg.

  17. 2) What date is it today? • Got Ya !!!!!

  18. Dalton’s Law of Partial Pressures • If there is more than one gas present, the total Pressure = sum of pressures of each gas • Pt = Pa + Pb + …….. + Pz • Let’s do a simple example.

  19. Avogadro’s Law • The volume of a gas at STP is proportional to the number of moles present. V = k n • V , Volume in L • k , k molar constant (22.4L/mol) • n , moles

  20. Ideal gas Equation • Most gases act as ideal gases except when close to 0K and/or under extreme pressure. • Boyles Law, Charles Law and Avogadro’s Law can be combined into an all-purpose Law allowing any “gas problem” to be solved (kind of like Beano) called the Ideal gas Law

  21. Ideal Gas Law PV = nRT n , moles of gas • V, Volume (L) • P , pressure (atm) • T , temperature (K) • R , Ideal gas constant (0.0821 atm-L/mol-K) • For problems with initial and final conditions, use….. • P1V1 / T1 = P2V2 / T2

  22. There are lots of examples: • What happens the temperature and pressure of CO2 gas in a paintball gun when it fires? • What happens the temperature and pressure of wind as it blows up a slope? • What happens the temperature and pressure of wind as it blows down a slope? • What happens the temperature and pressure of air in a pump? • The above example explains how a diesel engine works. Can you think of any other examples?

  23. Some things to know about gases – CH13.5 • Lifting power of gases: • All objects in a gas have a buoyant force on them. This force is in the upward direction. It depends on the size of the object. • Weight is a force in the downward direction. • A balloon with a light gas in it has a smaller weight than one with a heavier gas. Can you think of some light gases? • If buoyant force on the balloon > weight, balloon rises. If buoyant force<weight, it descends.

  24. A way to make a gas less dense is by heating. • A more expensive way is to use He gas or H2. • What would be an advantage of each?

  25. The ozone hole – causes/effects

  26. Ozone (O3) is formed by the action of sunlight on O2 in the upper stratosphere. • Ozone filters out most harmful U.V. rays. • Some manmade substances – chlorofluorocarbons (CFC’s) in particular cause this reaction to be reversed, destroying Ozone. • CFC’s are used in refrigerators, air conditioners and some plastic foam products. • An ozone hole developed over the Arctic and Antarctic with reduced levels of ozone worldwide. • Since most CFC production has been banned since 1980, the problem has improved somewhat.

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