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Gases

Gases. What are Characteristics of a GAS?. E X P A N D A B L E. Diffusible. Fluid. Compressible. Low Density. Ideal Gases. Real Gases. Gases have mass. Gases have no mass. Gases have no volume. Gases have volume. Gases do not interact – elastic collisions.

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Gases

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  1. Gases

  2. What are Characteristics of a GAS? E X P A N D A B L E Diffusible... Fluid Compressible Low Density

  3. Ideal Gases Real Gases Gases have mass. Gases have no mass. Gases have no volume. Gases have volume. Gases do not interact – elastic collisions. Gases exert forces on each other. Real World Assumptions

  4. F P = A What does PRESSURE mean? • In Life: Pressure = a stoichiometry quiz every day • In Science: • Pressure = force per unit area PSI = Pounds per Square Inch

  5. How else can we measure Pressure? 760 mm Hg 1 atmosphere = 760 torr 101.3 kilopascals These numbers reflect STANDARD PRESSURE

  6. S T P Standard Temperature & Pressure 273 K 1 atmosphere (atm)

  7. How is pressure measured? A barometer is a device used to measure atmospheric pressure. The first type of barometer introduced by Torricelli in the early 1600s.

  8. How can we change Gases? Action Variable Heat it up/Cool it down Temperature Change container size Volume Compress or Decompress Pressure

  9. How are Temperature and Volume Related? Initial Final T1 T2 Temperature V1 V2 Volume

  10. How are Temperature and Volume Related? x x x x x x x Volume x x x x x x Temperature “At constant pressure… temperature and volume are directly proportional.”

  11. Charles’ Law V1 V2 = T1 T2 “At constant pressure… temperature and volume are directly proportional.” Temperature is always measured in Kelvin! 0ºC = 273 K

  12. How can we change Gases? Action Variable Heat it up/Cool it down Temperature Change container size Volume Compress or Decompress Pressure

  13. How are Volume and Pressure Related? Initial Final V1 V2 Volume P1 P2 Pressure

  14. How are Volume and Pressure Related? x x x x x x x Volume x x x x x x Pressure “At constant temperature… volume and pressure are inversely proportional.”

  15. P1 V1 = P2 V2 x x Boyle’s Law “At constant temperature… volume and pressure are inversely proportional.”

  16. How are Temperature and Pressure Related? Initial Final T1 T2 Temperature P1 P2 Pressure

  17. How are Temperature and Pressure Related? x x x x x x x Pressure x x x x x x Temperature “At a constant volume… temperature and pressure are directly proportional.”

  18. Gay-Lussac’s Law P1 P2 = T1 T2 “At a constant volume… temperature and pressure are directly proportional.” Temperature is always measured in Kelvin! 0ºC = 273 K

  19. V1 V2 = T1 T2 P1 V1 = P2 V2 x x To Recap… • Charles’ Law: Relates Temperature and Volume. • Boyle’s Law: • Relates Pressure and Volume

  20. P1 P2 = T1 T2 • Gay-Lussac’s Law: • Relates Temperature and Pressure.

  21. P1 V1 P2 V2 T1 T2 …THEREFORE: • Temperature, Volume, and Pressure are all related! = Combined Gas Law

  22. We that we live in an world where: Gas particles have no mass Gas particles have no volume Gas particles have elastic collisions A Reminder… assume ideal These assumptions are used when trying to calculate the AMOUNT of a gas we have!

  23. Why are these assumptions important? PV = nRT

  24. PV = nRT Ideal Gas Law PRESSURE VOLUME n MOLES OF GAS R GAS CONSTANT TEMPERATURE mmm...PiVNeRT

  25. 8.31 kPa · L 0.0821 atm · L mol · K mol · K 62.4 mmHg · L mol · K The MysteRious R • R is a constant (doesn’t change). • Number value of R depends on other units. • Units of R are a combination of many units.

  26. What? PV = nRT Solve for R: P V R = n T Plug in units: (mm Hg) (L) (kPa) (atm) R = (mol) (K)

  27. V1 V2 = T1 T2 P1 V1 P2 V2 = T1 T2 Gas Laws, Gas Laws Everywhere! Charles' Law Boyle's Law P1 x V1 = P2 x V2 Combined Gas Law Ideal Gas Law Used with CHANGING CONDITIONS P V = n R T Used with only ONE SET OF CONDITIONS

  28. When to Use PV = nRT • Calculating amount of gas in moles • Calculating P, V, or T if moles of gas are known. • IMPORTANT! We must have 3 out of 4 pieces of information: • P • V • n • T

  29. How do the gas laws apply to gas mixtures, like air? In a mixture of nonreacting gases, each gas contributes to the total pressure in proportion to the fraction (by volume) in which it is present. This contribution is called the partial pressure of the gas. “The sum of the individual pressures is equal to the total pressure.” Total Pressure = Pressure of gas 1 + Pressure of gas 2 + Pressure of gas 3 + Pressure of gas 4 … Ptotal = P1 + P2 + P3 + … Dalton's Law of Partial Pressures

  30. Molar Volume of a Gas Do you remember the value of one mole? 6.02 x 1023

  31. One mole of oxygen, O2, contains 6.022 x 1023 oxygen molecules and has a mass of 31.99 g. One mole of helium gas has a mass of 4.002 g. Does helium have the same number of molecules? Yes! Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Avogadro's Law

  32. Will 1 mole of O2 gas and 1 mole of He gas occupy the same volume (at the same temperature and pressure) despite different masses? Yes! Remember, according to Avogadro’s law, one mole of any gas will occupy the same volume as one mole of any other gas at the same temperature and pressure, despite mass differences. Standard Molar Volume of a Gas The volume occupied by one mole of gas at STP. It has been found to be 22.41410 L.

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