Class Note for CHEM 122 at UMass(38)
Class Note for CHEM 122 at UMass(38)
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This 2 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Massachusetts taught by a professor in Fall. Since its upload, it has received 18 views.
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Date Created: 02/06/15
Chapter 13 Lecture Worksheet 3 1A The radioactive isotope 64Cu is used in the form of copperll acetate to study Wilson39s disease The isotope has a halfilife of 1270 hours What fraction of radioactive copperll acetate remains after 48 hours 2 days 7 Know Radio Active Decay First Order kinetics Many ways to write integrated rate law 1n64 Cu kt ln54Cuo 54 64 112 kl 671 Prove the last statement it 0 u 0 Also know ln2 tm 7 1270h t48h k Looking for Fraction of 64Cu remaining Fraction means amount of interest divided by the total 64 Cu 64 Culo Translate into mathematical statement gt Eguation Use the equation that is closest to what you are looking for 5404 1 mm 1 Ash1270 5 7 7 00728 10 2 2 Reasonable 7 About 7 remains after 38 halfilives 7 First halfilife 50 Second halfilife 25 Third 125 Fourth 625 REASONBLE 1B How much time is required to reduce the fraction to 10396 1 part per million 7 I 64 Cu 76 I I Know W 10 Looking for t 7 5 Cu 1H2 Eguation ln 7 kt 7 t 54 CuL rm Solve for t Substitute values Do the arithmetic Round to 4 significant figures 64 M1n754 0 j 123970h1n10 5 ln2 Cull ln2 253 h 1 day24h 1055 days 2 Nitrogen oxide emissions are a major source of air pollution Consider the decomposition of dinitrogen pentaoxide 2 N205 g gt 4 N02 g 02 g A What data should you collect in order to determine the rate constant for this reaction 7 N205 vs time data B What data should you collect in order to determine the Energy of Activation for this reaction 7 k vs Temperature C How can you plot the data in question 3 to determine the Energy of Activation From the linear form of the Arrhenius Equation lnk E lnA RT ln k slope EaR 1T X aXis 1T Y aXis ln k D From this plot Ea R slope 3 When heated to a high temperature cyclopropane is converted to propene At 4700C the rate constant for this reaction is 110 X 104 s l At 5100C the rate constant for this reaction is 102 X 10 3 s l What is the energy of activation for this reaction 1 Cyclopropane C 3H6 2 Propene C3H6 Know T1 470 C 273 743 K k1 110 x1071 5 1 T2 510 C 273 783 K k2 102 x103 5 1 Looking for Ea Equation Need equation that relates TEMPERATURE k and Ea 22gt Arrhenius Equation Many ways to write it Use the equation that is closest to what you are looking for E kAeRT lnk E lnA ln g RT k1 Solve for Ea Do the arithmetic Round to 3 significant figures 1 1 1 1 k1 110x10 4s 1 T2 71 R lnk2 83l4JmolK 1 102x10 3s 1 1 1 783K 743K 269300 Jmol 1 kJ1000 J 269 kJmol Note It is very easy to make mistakes on these calculations Common mistakes Forget to convert to Kelvin temperature Incorrect sign Ea is ALWAYS positive think about it The 1T calculation is negative because T2 gt T1 Convert to kilojoules incorrectly Get units wrong DON39T DROP UNITS Use incorrect R Must be in ENERGY units If you keep units on R you WON39T make this mistake LIIlme
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