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Test 3 De-Briefing

Test 3 De-Briefing. Overall Averages:. Test corrections due Thursday. Part 1: MC. MC Troublespots. #1 Right idea, wrong shape… #5 A way to simplify: Remember molar volume at STP? #7 A way to organize:. More MC Troubles. #12-16. Rats #17-18. Rats again. Thermochemistry = 

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Test 3 De-Briefing

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  1. Test 3 De-Briefing Overall Averages: Test corrections due Thursday

  2. Part 1: MC

  3. MC Troublespots #1 Right idea, wrong shape… #5 A way to simplify: Remember molar volume at STP? #7 A way to organize:

  4. More MC Troubles #12-16. Rats #17-18. Rats again. Thermochemistry =  #22 – Think stoich #26-28 – How do concentration and heat affect rate??? #30 – If double 1st order, rate will…

  5. #31 – A Visual Initial Rates Method

  6. Part 2: Quantitative Free Response

  7. First Half #1 – OK #2a – Forgot to do stoich! Mols B2H6→ ? Mols H2? #2c – Eh? #2d -  #2e – Stoich w/heat! #2f - OK BH3 - Borane B2H6 – Diborane Crazy, huh?

  8. #3 – Method of Initial Rates 3a&b -  3c – Units? 3d – Eh? More stoich! 6 H2O from 1 B2H6 3e – Not bad.

  9. #4 – Integrated Rate Laws Ugg. As in Ugg-ly. But some bright spots • OK • Slope? (OK, it was an ugly graph, too. I’m sorry) •  • BH3 is made from B2H6 already reacted, not what B2H6 is still left • A little disappointing

  10. Part 3: Qualitative FR

  11. Question 1a Possible Answers…What’s Wrong? • More moles He cuz atoms are smaller, so more are needed to fill space. Does size matter when it comes to how much can fit? SF6 d = 380 pm Space per particle d = 4,400 pm He d = 62 pm

  12. Another Common Answer to 1a He has the lowest molar mass, so need more. What’s wrong? Is mass the same for all flasks? PV = nRT: take it for a spin.

  13. 1B Kinetic energy has TWO factors: KE = ½ mv2 Mass AND Velocity! Nevertheless, a gas’s kinetic energy depends ONLY on its ___________. (A gas’s particles will “adjust” their velocity to achieve this kinetic energy)

  14. 1B Can a charging rhinoceros and a charging mouse have the same kinetic energy? Answer: Yes, if the mouse is traveling 3,800 m/s (8,700 mph, Mach 11)!

  15. 2a • Methane = CH4 (I feel only a little bad) • Catalysis is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. …Catalysts work by providing an (alternative) mechanism involving a different transition state and lower activation energy. - Wikipedia (emphasis on “chemical substance” added) • A spark is NOT a catalyst, it is energy…

  16. 2b • Mole fraction = mols of Gas A / Total mols of gas • Partial pressure = mol fraction × Total pressure

  17. 3a-c

  18. More Q3 • 3d =  • 3e = Look down there • 3f =  Follow me to Lab 11 Results

  19. RATE? 3g For 1st order reactionsPlot [A] vs. time: slope = Rate Plot ln[A] vs. time: slope = -k Failure of integrated rate law to tell rate: ln[A] = -kt + ln[A]0

  20. A Word About Finals • 6th Hour: Friday 8:15 – 10:05 • In my room (Room 105) • Will (quietly) leave during 6th hour Final Period • 8th Hour: Thursday 12:25 – 2:15 • In my room (Room 105) • Will leave during 7th hour class Feel free to drop in for extra help (just not during 1st, 2nd, or 3rdFinal periods)

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