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Chapter 5

Chapter 5. The Gaseous State. HST. Mr . Watson. Properties of Gases. can be compressed exert pressure on whatever surrounds them expand into whatever volume is available easily diffuse into one another

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Chapter 5

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  1. Chapter 5 The Gaseous State HST Mr. Watson

  2. Properties of Gases • can be compressed • exert pressure on whatever surrounds them • expand into whatever volume is available • easily diffuse into one another • can be described in terms of their temperatures and pressure,the volume occupied, and the amount (number of molecules or moles) present

  3. Mercury Barometer

  4. Composition of Air at Sea Level

  5. Important Units of Pressure Conversion factor to learn

  6. Boyle’s Law At constant temperature and mass of gas: Va1/P V = a * 1/P where a is a proportionality constant thus VP = a V1P1 = a = V2P2 V1P1 = V2P2

  7. Boyle’s Law

  8. Boyle’s Law

  9. Charles’ Law At constant pressure and mass of gas: VaT V = b * T where b is a proportionality constant V/T = b V1/T1 = b = V2/T2 V1/T1 = V2/T2

  10. Charles’ Law

  11. Combined Gas Law At constant mass of gas VaT/P V = d * (T/P) where d is a proportionality constant (VP)/T = d V1P1 = d = V2P2 T1 T2 V1P1 = V2P2 T1 T2

  12. Avogadro’s Law At constant pressure and temperature Van V = c * n where c is a proportionality constant V/n = c V1/n1 = c = V2 /n2 V1/n1 = V2 /n2

  13. Ideal Gas Law Va(n * T)/P V = R * (n * T)/P where R is proportionality constant P * V = n * R * T (P*V)/(n*T) =R Thus, (P1*V1)/(n1*T1) = (P2*V2)/(n2*T2)

  14. What will be volume of an ideal gas at absolute zero? - 10 mL/mole 0 mL/mole 10 mL/mole

  15. Ideal Gas Constant R = 0.08205 L*atm/mol*K R has other values for other sets of units. R = 82.05 mL*atm/mol*K = 8.314 J/mol*K = 1.987 cal/mol*K

  16. Molar Massfrom Gas Density gas density = #g/V = d PV = nRT where n = #g/MM PV = (#g/MM)*RT MM = (#g*R*T)/(P*V) MM = (#g/V)*((R*T)/P) = (d*R*T)/P

  17. Dalton’s Lawof Partial Pressures The total pressure of a mixture of gases is equal to the sum of the pressures of the individual gases (partial pressures). PT = P1 + P2 + P3 + P4 + . . . . where PT => total pressure P1 => partial pressure of gas 1 P2 => partial pressure of gas 2 P3 => partial pressure of gas 3 P4 => partial pressure of gas 4

  18. Dalton’s Law of Partial Pressure

  19. Collecting Gases over Water

  20. Example: What volume will 25.0 g O2 occupy at 20oC and a pressure of 0.880 atm? (25.0 g)(1 mol) n = ---------------------- = 0.781 mol (32.0 g) V =?; P = 0.880 atm; T = (20 + 273)K = 293K R = 0.08205 L*atm/mol*K V = nRT/P = (0.781 mol)(0.08205L*atm/mol*K)(293K) 0.880atm = 21.3 L

  21. Example: A student generates oxygen gas and collects it over water. If the volume of the gas is 245 mL and the barometric pressure is 758 torr at 25oC, what is the volume of the “dry” oxygen gas at STP? (Pwater = 23.8 torr at 25oC) PO2 = Pbar - Pwater = (758 - 23.8) torr = 734 torr

  22. ExampleA student generates oxygen gas and collects it over water. If the volume of the gas is 245 mL and the barometric pressure is 758 torr at 25oC, what is the volume of the “dry” oxygen gas at STP? Pwater = 23.8 torr at 25oC; PO2 = Pbar - Pwater = (758 - 23.8) torr = 734 torr P1= PO2 = 734 torr; P2= SP = 760. torr V1= 245mL; T1= 298K; T2= 273K; V2= ? (V1P1/T1) = (V2P2/T2) V2= (V1P1T2)/(T1P2) = (245mL)(734torr)(273K) (298K)(760.torr) = 217mL

  23. Kinetic Molecular Theory Matter consists of particles (atoms or molecules) in continuous, random motion.

  24. Kinetic Molecular Theory: Gases • particles in continuous, random, rapid motion • collisions between particles are elastic • volume occupied by the particles has a negligibly small effect on their behavior • attractive forces between particles have a negligible effect on their behavior • gases have no fixed volume or shape, take the volume and shape of the container

  25. Maxwell’s Distribution of Speeds

  26. Real Gases • have a finite volume at absolute zero • have attractive forces between gas particles

  27. Van der Waals Equation (P + a/V2)(V - b) = nRT where a => attractive forces b => residual volume

  28. Carbon Dioxide and Greenhouse Effect

  29. Some Oxides of Nitrogen • N2O • NO • NO2 • N2O4 2 NO2 = N2O4 brown colorless • NOx

  30. Air Pollution in Los Angles

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