1. PowerPoint to accompany Chapter 9b-2 Gases

2. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Dalton’s Law of Partial Pressures  The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone.  In other words, P total = P 1 + P 2 + P 3 + …

3. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Partial Pressures and Mole Fraction Since P 1 = n 1 RT/V Then P 1 = n 1 RT/V P 2 = n 2 RT/V = n1n1 n2n2 = X (mole fraction)

4. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Partial Pressures and Mole Fraction  So, when one collects a gas over water, there is water vapour mixed in with the gas.  To find only the pressure of the desired gas, one must subtract the vapour pressure of water from the total pressure. Figure 9.13

5. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Kinetic-Molecular Theory 1. Gases consist of large numbers of molecules that are in continuous, random motion. 2. The combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained. 3. Attractive and repulsive forces between gas molecules are negligible. (See note*)

6. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia

7. N 2 =28g/M Maxwell-Boltzmann Distribution

8. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Maxwell-Boltzmann Distribution

9. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Kinetic-Molecular Theory 4. Energy can be transferred between molecules during collisions, but the average kinetic energy of the molecules does not change with time, as long as the temperature of the gas remains constant. 5. The average kinetic energy of the molecules is proportional to the absolute temperature.

10. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Molecular Effusion and Diffusion Effusion The escape of gas molecules through a tiny hole into an evacuated space. Diffusion The spread of one substance throughout a space or throughout a second substance. Figure 9.17 Gas Molecules spread uniformly You cannae hide a fert!

11. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Tae a Fert, Roy Williamson  Oh what a sleekit horrible beastie Lurks in yer belly efter the feastie Just as ye set doon among yer kin There sterts to stir an enormous wind.  The neeps and tatties and mushy peas Stert workin like a gentle breeze But soon the puddin wi the sauncie face Will have ye blawin’ all ower the place.  Nae matter whit the hell ye dae A’bodys gonnae have tae pay Even if ye try to stifle, It’s like a bullet oot a rifle.  Hawd yer bum tight tae the chair Tae try and stop the leakin air Shift yersel frae cheek tae cheek Prae tae God it disnae reek.  But aw yer efforts go assunder Oot it comes like a clap o’ thunder Ricochets aroon the room Michty me, a sonic boom!  God almighty it fairly reeks; Hope I huvnae shit ma breeks Tae the bog I better scurry Aw whit the hell, its no ma worry.  A’body roon aboot me chokin, Wan or two are nearly bokin I’ll feel better for a while Cannae help but raise a smile.  Wis him! I shout with accusin glower, Alas too late, he’s just keeled ower Ye dirty bugger they shout and stare I dinnae feel welcome any mair.  Where ere ye go, let yer wind gan free Soonds like just the job fur me Whit a fuss at Rabbie's perty Ower the sake o won wee ferty.

12. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Graham’s Law of Effusion & Diffusion  The ratio of the rates of effusion of two gases is equal to the square root of the inverse ratio of their molecular masses or densities.  The effusion rate of a gas is inversely proportional to the square root of its molecular mass.  Mathematically, this can be represented as:  Rate1 / Rate2 = square root of (Mass2 / Mass 1)

13. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Graham’s Law of Effusion & Diffusion  For the 2 common gases in air: the rate off effusion of Nitrogen and Oxygen.  N 2, Nitrogen, has a molecular mass of 28.0 g. O 2, Oxygen, has a molecular mass of 32.0 g. Therefore, to find the ratio, the equation would be:  RateN 2 /RateO 2 = square root of 32.0 g / 28.0 g.  This works out to: RateN 2 /RateO 2 = 1.069

14. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia

15.  Gas X 2 effuses at 0.355 times that of O 2  r x2 = 0.355 r O2  r x2 / r O2 = 0.355 = SQRT [(32.0 g/Mol)/Mx 2 ]  (32.0 g/Mol)/ Mx 2 ) = (0.355) 2 = 0.126  Mx 2 = (32.0 g/Mol)/0.126 = 254 g/Mol  X g/Mol = 254/2 = 127 g/Mol  Iodine is 126.9 so the gas was I 2  Since WWII we have separated 2 Uranium isotopes 235 from 238 as UF 6 gas  r 235 / r 238 = sqrt (352.04/349.03) = 1.0043 Applying Graham’s Law of Effusion

16. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia The mean free path.

17. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Real Gases Figure 9.21 In the real world, the behaviour of gases only conforms to the ideal-gas equation at: relatively high temperature and low pressure, low gas concentrations, low molecular weights and simple symmetric molecules or atoms. For n=1, for H 2 (blue) and heavier gases (red, green). Note that heavy gases are attractive at low pressure & all are repulsive at high pressure. Why?

18. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia Deviations from Ideal Behaviour The assumptions made in the kinetic-molecular model break down at high pressure and/or low temperature. Figure 9.22Figure 9.23

19. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia

20. Corrections for Non-ideal Behaviour  The ideal-gas equation can be adjusted to take these deviations from ideal behaviour into account.  The corrected ideal-gas equation is known as the van der Waals equation.  nRT n 2 a  P = --------- - --------  V – nb V 2

21. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia The van der Waals Equation ) (V − nb) = nRT n2aV2n2aV2 (P + Table 9.2

22. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia

23. Examples of Gas Chemistry & Physics in the Real World  Atmospheric pollution: industry, engines, cows  O 3 generating & destroying reactions  Volcanic aerosols  Warfare: Cl 2, Sarin, Mustard Gas, Phosgene  Photosynthesis, O 2 and the Carbon cycle  Rocket & Jet Propulsion  Gas Shocks, Combustion Engines  Perfume and pheromones  Clathrates and Gas Hydrates  Explosives

24. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia End of Part 9b2:  Real Gas Applications