Gases

1. Gases

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

3. Physical Characteristics of Gases • Gases assume the volume and shape of their containers. • Gases are the most compressible state of matter. • Gases will mix evenly and completely when confined to the same container. • Gases have much lower densities than liquids and solids.

4. Kinetic Theory of Gases • KMT Based on 5 Assumptions: • G. have large number of particles that are very far apart from each other relative to their size. • Collisions between g. particles and between g. particles and container walls are elastic. (No net loss of kinetic energy)

5. Kinetic Theory of Gases cont. G. particles are in constant motion There are no forces of attraction between G. particles. The temperature of a gas depends on the average kinetic energy of the particles of the gas. KE= ½ (mv2). All gases have the same KE at the same temperature.

6. Ideal vs. Real Gases • Ideal gas: hypothetical gas that perfectly fits all of the assumptions of the KMT. • Real gas: one that does not behave exactly according to the assumptions of the KMT. • Real gas behavior more likely at high pressures and low temperatures.

7. Questions What happens to gas particles when a gas is compressed? What happens to gas particles when a gas is heated? Describe the conditions under which a real gas is most likely to behave ideally.

8. Gases and Pressure • Pressure: Force per unit area. Pressure = Units of Pressure 1 pascal (Pa) = 1 N/m2 1 atm = 760 mmHg = 760 torr 1 atm = 101,325 Pa

9. 4/16/2012 Get out your notebooks and your books if you have them.

10. Gases and Pressure Gases • Calculate the pressure of the following: • F=500N, A= 325cm2 • F=500N, A= 13cm2 • F=500N, A= 6.5cm2

11. Gases and Pressure Gases • Convert the following pressures: • P = 0.830atm to mmHg, and kPa • P = 1.75atm to mmHg and kPa • The critical pressure of carbon dioxide is 72.7atm, what is this value in Pa?

12. Gases and Pressure Gases • Standard Temperature and Pressure (STP) • = 1atm and 0°C

13. Dalton’s Law of Partial Pressures Gases • The pressure of each gas in a mixture is the partial pressure of that gas. • Dalton’s Law of partial pressures = the total pressure of a gas mixture is the sum of all the partial pressures of the component gases. • PT = P1 + P2 + P3 + ….

14. Dalton’s Law of Partial Pressures Gases • Water Displacement, gas collected over water. • Always mixed with water vapor, which has specific water pressure. • Patm = Pgas + PH2O

15. Dalton’s Law of Partial Pressures Gases • Three of the primary components of air are CO2, O2, and N2. In the sample containing a mixture of only these gases at exactly 1atm, the partial pressures of PCO2 = 0.285 torr and PN2 = 593.525 torr. What is the partial pressure of oxygen?

16. Dalton’s Law of Partial Pressures Gases • Oxygen gas from decomposition of KClO3, was collected by water displacement. The barometric pressure and temperature was 731.0 torr and 20.0°C. What was the partial pressure of the oxygen collected?

17. 4/19/2012 Get out your notebooks

18. Boyle’s Law • Volume of a fixed mass of gas varies inversely with pressure at a constant temperature. • PV = k , k is a constant • Product always remains the same, so can be written: • P1V1 = P2V2

19. Boyle’s Law Constant temperature Constant amount of gas

20. 726 mmHg x 946 mL P1 x V1 = 154 mL V2 A sample of chlorine gas occupies a volume of 946 mL at a pressure of 726 mmHg. What is the pressure of the gas (in mmHg) if the volume is reduced at constant temperature to 154 mL? P1 x V1 = P2 x V2 P1 = 726 mmHg P2 = ? V1 = 946 mL V2 = 154 mL P2 = = 4460 mmHg

21. Charle’s Law • Volume of a fixed mass of gas at constant pressure varies directly with the Kelvin Temperature. • V = kT , k is a constant or

22. Charle’s Law • Kelvin Scale: -273.15ºC, or 0 K. Absolute Zero at which all movement stops. • K = 273.15 + ºC • Convert 50ºC to K • K = 273.15 +50 • K = 223.15K

23. Charle’s Law

24. 1.54 L x 398.15 K V2 x T1 = 3.20 L V1 A sample of carbon monoxide gas occupies 3.20 L at 125 0C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant? V1/T1 = V2/T2 V1 = 3.20 L V2 = 1.54 L T1 = 398.15 K T2 = ? T2 = = 192 K

25. Guy-Lussac’s Law • Pressure of a fixed mass of gas at a constant temperature varies directly with the Kelvin Temperature. • P = kT , k is a constant or

26. 325.15 K x 3.00atm T2 x P1 = 298.15 K T1 The gas in a container is at a pressure of 3.00atm at 25ºC. Directions on the container warn the user not to keep it in a place where the temp. exceeds 52ºC. What would the pressure in the container be at that temp? P1/T1 = P2/T2 P1 = 3.00 atm P2 = ? T1 = 298.15 K T2 = 325.15K P2 = = 3.27atm

27. Combined Gas Law • Expression of the relationship between pressure, volume and temperature of a fixed amount of gas.

28. 283.15 K x 1.08atm x 50.0L T2 x P1 x V1 = 298.15 K x 0.855atm P2 x T1 Combined Gas Law A helium filled balloon has a volume of 50.0L at 25ºC and 1.08atm. What volume will it have at 0.855atm and 10.0ºC. P1 = 1.08 atm P2 = 0.855atm T1 = 298.15 K T2 = 283.15 K V1 = 50.0 L V2 = ? V2 = = 60.0L

29. Constant temperature Constant pressure Avogadro’s Law Va number of moles (n) V = k x n

30. 4NH3 + 5O2 4NO + 6H2O 1 volume NH3 1 volume NO 1 mole NH3 1 mole NO Ammonia burns in oxygen to form nitric oxide (NO) and water vapor. How many volumes of NO are obtained from one volume of ammonia at the same temperature and pressure? At constant T and P

31. Avogadro’s Law Standard Molar Volume: Volume occupied by 1 mole at STP = 22.4L 1mol gas = 22.4L gas What Volume does 0.0685mol of gas occupy at STP? Multiply the amount in moles by the conversion factor, 1mol gas = 22.4L gas

32. What quantity of gas, in moles, is contained in 2.21L at STP? Multiply the volume in liters by the conversion factor, 1mol gas = 22.4L gas

33. Boyle’s law: V a (at constant n and T) Va nT nT nT P P P V = constant x = R 1 P Ideal Gas Equation Charles’ law: VaT(at constant n and P) Avogadro’s law: V a n(at constant P and T) R is the gas constant PV = nRT

34. The conditions 0 0C and 1 atm are called standard temperature and pressure (STP). Experiments show that at STP, 1 mole of an ideal gas occupies 22.414 L. R = (1 atm)(22.414L) PV = nT (1 mol)(273.15 K) PV = nRT R = 0.082057 L • atm / (mol • K)

35. 1 mol HCl V = n = 49.8 g x = 1.37 mol 36.45 g HCl 1.37 mol x 0.0821 x 273.15 K V = 1 atm nRT L•atm P mol•K What is the volume (in liters) occupied by 49.8 g of HCl at STP? T = 0 0C = 273.15 K P = 1 atm PV = nRT V = 30.6 L

36. P1 = 1.20 atm P2 = ? T1 = 291 K T2 = 358 K nR P = = T V P1 P2 T2 358 K T1 T1 T2 291 K = 1.20 atm x P2 = P1 x Argon is an inert gas used in lightbulbs to retard the vaporization of the filament. A certain lightbulb containing argon at 1.20 atm and 18 0C is heated to 85 0C at constant volume. What is the final pressure of argon in the lightbulb (in atm)? n, V and Rare constant PV = nRT = constant = 1.48 atm

37. What is the volume of CO2 produced at 370 C and 1.00 atm when 5.60 g of glucose are used up in the reaction: C6H12O6 (s) + 6O2 (g) 6CO2 (g) + 6H2O (l) 6 mol CO2 g C6H12O6 mol C6H12O6 mol CO2V CO2 x 1 mol C6H12O6 1 mol C6H12O6 x 180 g C6H12O6 L•atm mol•K nRT 0.187 mol x 0.0821 x 310.15 K = P 1.00 atm Gas Stoichiometry 5.60 g C6H12O6 = 0.187 mol CO2 V = = 4.76 L

38. 0.116 8.24 + 0.421 + 0.116 A sample of natural gas contains 8.24 moles of CH4, 0.421 moles of C2H6, and 0.116 moles of C3H8. If the total pressure of the gases is 1.37 atm, what is the partial pressure of propane (C3H8)? Pi = XiPT PT = 1.37 atm = 0.0132 Xpropane = Ppropane = 0.0132 x 1.37 atm = 0.0181 atm

39. NH4Cl Gas diffusion is the gradual mixing of molecules of one gas with molecules of another by virtue of their kinetic properties. Gas effusion is the process by which gas particles pass through a tiny opening. NH3 17 g/mol HCl 36 g/mol