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Gas Laws

Gas Laws. The work of Boyles, Charles, Dalton, Graham and other scientists explains the behavior of gases. . High temperatures and low pressures. Kinetic Molecular Theory. Explanation of how IDEAL gas particles behave move in constant, random, straight-line motion

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Gas Laws

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  1. Gas Laws The work of Boyles, Charles, Dalton, Graham and other scientists explains the behavior of gases.

  2. High temperatures and low pressures Kinetic Molecular Theory • Explanation of how IDEAL gas particles behave • move in constant, random, straight-line motion • undergo “elastic” collisions • transfer energy • Particles are volumeless • no intermolecular attractions

  3. Deviations from Ideal Behavior • No gas behaves perfectly all the time • Major deviations are seen at low temperatures COLD and high pressures SQUEEZED • Lose E • Attractions form between particles • Not in constant motion • Particles have volume

  4. You know gases are behaving like ideal gases if they mathematically conform to these gas laws.

  5. Boyle’s Law constant (T)emperature • Relationship between (P)ressure and (V)olume

  6. A decrease in volume results in an increase in pressure

  7. Inverse relationship • P1V1=P2V2= P3V3. . .constant value

  8. Practice P1V1 = P2V2 • A sample of gas under a pressure of 822kPa has a volume of 312ml. The pressure is increased to 948kPa. What volume will the gas occupy? • The volume of a gas is .2L when the pressure is 9.25atm. If the volume is increased to 306mL what is the new pressure?

  9. Charles’ Law

  10. Charles’ Lawconstant pressure • Relationship between temperature and volume • Volume of a Balloon

  11. V T Volume is directly proportional to Temperature in Kelvin K = oC + 273 V  T V  T

  12. Volume Temperature K Constant pressure graph V1/T1 = V2/T2

  13. Practice • A sample of a gas has a volume of 152mL when its temperature is 18oC. If its temperature is increased to 32oC, what will the volume become?

  14. Relationship between Temperature and Pressureconstant volume • As the molecules move faster they collide more with the walls of their container  P if volume remains the same P1/T1 = P2/T2

  15. Practice • At a temperature of -33.0oC, a sample of confined gas exerts a pressure of 53.3kPa. If volume remains constant, at what temperature will the pressure reach 133kPa?

  16. V P Gas Lawssummary

  17. It is often necessary to determine relationships between (P)ressure (V)olume (T)emperature Kelvin! P1V1 = P2V2 T1 T2 COMBINEDGas Laws

  18. Practice • A sample of oxygen gas has a volume of 205mL when its temperature is 22.0oC and its pressure is 30.8kPa. What volume will the gas occupy at STP?

  19. Remains the same Density of Gas • The density of a gas varies widely depending on temperature and pressure D = m/v

  20. Hints to Density problems • Write down everything known and unknown in the problem • Before you find D you must find V2 • If D is given, immediately find mass and volume if D=5g/L then m=5g v=1L • Mass stays constant • If no mass is given do STOICH!

  21. Avogadro’s Law • Equal volumes of gases under the same conditions of temperature and pressure contain the same number of molecules. • Lower volume: less molecules • Higher volume: more molecules

  22. You can only compare volumes (number of molecules) WHEN the samples are at the SAME TEMPERATURE AND PRESSURE So you may have to do the math! • Which container has the least number of molecules? 4L of CO2 at STP 3L of N2 at 2atm & 20oC

  23. Dalton’s Law • In a containerwhere a mixture of gases is present, the total pressure of the mixture is equal to the sum of the partial pressures for each of the gases • PTotal = P1 + P2 + P3 . . .

  24. A 600mL container is filled with 200mL of hydrogen and 400mL of oxygen. The total pressure in the container is 75kPa, what is the partial pressure of each gas? 25kPa = Hydrogen 50kPa = Oxygen There is twice as much oxygen so it exerts twice as much pressure

  25. Graham’s Law • Molecules of higher molecular mass diffuse more slowly as compared to molecules of lower molecular mass. F2 Cl2 H2 Ne Kr

  26. The End

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