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Announcements

Announcements. To join clicker to class today: Turn on the Clicker (the red LED comes on). Push “Join” button followed by “20” followed by the “Send” button (switches to flashing green LED if successful). Exam 4 on Chapters 7 & 8 Wednesday. Discussion—quiz on 8.1-8.7 & Review.

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Announcements

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  1. Announcements • To join clicker to class today: • Turn on the Clicker (the red LED comes on). • Push “Join” button followed by “20” followed by the “Send” button (switches to flashing green LED if successful). • Exam 4 on Chapters 7 & 8 Wednesday. • Discussion—quiz on 8.1-8.7 & Review. • Wear appropriate clothes to Lab! • Do not forget about the Lewis Tutorial, the VSEPR examples on Web site and the text site, as well, for more examples and pictures. • Will start Chapter 9 after exam. • Celebration of Scholarship this Thursday in Reeve.

  2. Review • PV = nRT • Solved for solve for any variable. • Partial pressures • Ptot = P1 + P2 + … = (n1 + n2 + …)RT/V • Pi = XiPtot • ∑i Xi = 1 or X1 + X2 + X3+ ... = 1 • Cgas = kHPgas • Kinetic Molecular Theory of Gases.

  3. Kinetic Molecular Theory of Gases • Molecules assumed to be very small (essentially points with no volume) • They are constantly moving and exchanging kinetic energy through elastic collisions => they are changing direction and speed randomly, but total kinetic energy constant. • Pressure = sum of the force of many collisions with the walls of the container. • Based on KE = (1/2)mu2 (u = speed). • Each sample has a distribution of speeds. • lighter particles move faster. • Key result: urms = (3RT/M)1/2 • Higher temperature => higher speeds.

  4. Diffusion and Effusion • urms = (3RT/M)1/2 • Diffusion = spread of one substance through another. • Effusion = process of a gas escaping through a small hole. • Rate for both depends on urms • Higher T => faster diffusion or effusion. • relative rates r1/r2 =urms(1)/urms(2) = (M2/M1)1/2

  5. Van der Waals gas equation P = nRT/(V-nb) -a(n/V)2 • P, V, n, R, T same as ideal gas law • b = volume taken up by 1 mole of molecules (increases P) • a = attraction factor (decreases P) Implications • If V is small (≈ nb) P will be much higher than expected. • If a is larger P will be lower than expected. • Ex: O2 at 10 atm of pressure in 1.00 L at 298 K (25 ˚C): Ideal gas law => 0.409 moles of gas. Using the van der Waals get 0.413 moles of gas.

  6. Using Van der Waals gas equation P = nRT/(V-nb) -a(n/V)2 • You must be able to: • use equation to calculate the actual pressure observed given all other values. • look at a and b to compare molecules and determine which is more affected by attraction or volume of the molecules. Example: For 2.560 x 10-4 mol H2O in 200.0 mL at 298.0 K ideal gas law gives a pressure of 3.130 x 10-2 atm. Use VDW calculate P. a(H2O) = 5.460 L2atm/mol2 b(H2O) = 0.03050 L/mol

  7. Chapter 7-Greenhouse effect, molecular vibrations and shape A. Greenhouse Effect B. Infrared Spectroscopy C. Lewis structures again D. Unpaired e- (MO diagram review) E. VSEPR model (3-D molecular shapes) F. Valence Bond Theory and 3-D shapes G. Dipole moments and shapes of molecules

  8. Chapter 8 – Gases • Pressure • Ideal Gas Law (PV = nRT, solutions for P, V, n, T, density and molar mass) • Dalton’s Law of Partial Pressures • Henry’s Law of gas solubility • Kinetic Molecular Theory of Gases (molecular speeds, diffusion and effusion) • Real Gases/Non-Ideal behavior (van der Waals equation)

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