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# 32 Note 5 for CHM 11500 with Professor Das at Purdue

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This 34 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at Purdue University taught by a professor in Fall. Since its upload, it has received 14 views.

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Date Created: 02/06/15

CHM 115 Dr Hilkka Kentt maa Lecture 5 Reading was 234 and 235 Lecture 6 237239 Summary from Previous Lecture E mc2 mass defect Nuclear reactions are different from other chemical reactions Atoms change identity Energy scale different Types of nuclear reactions vary and can be predicted Fraction of sample P Lu P P P P P m a I an to n P a P M P Radioactive Decay Follows Firstorder Kinetics D Decay uf Tcng 2 halflife 1112 6 h E 6 h A 1 MEL 6 h u u I 5 10 15 2t 25 3 35 4D Buddy Question 1 X is radioactive How much of a sample ofX is left after 3 halflives a 12 b 13 014 d18 e Impossible to tell without knowing the initial mass ofX and its half life Buddy Question 1 X is radioactive How much of a sample ofX is left after 3 halflives a12 gt gt b 13 014 Two halflife halflives l d 18 e Impossible to tell without knowing the initial m mass ofX and its half life Buddy Question 2 The halflife of 239Pu is 24000 years How much 239Pu remains in a sample that initially contained 10 kg of plutonium after 96000 years 12 kg 14 kg 18 kg d 116 kg 939 0 Buddy Question 2 The halflife of 239Pu is 24000 years How much 239Pu remains in a sample that initially contained 10 kg of plutonium after 96000 years 3 2 kg Time halflife halflives b 14 kg 96000 V 24000 y 4 gt 4 halflives 1 2 c 18 kg 1 kg gt 05 kg gt 025 kg d makg gt 0125 kg gt 00525 kg116 kg Nuclear Reactions Kinetics N decaying nuclei dN dt change in of nuclei per 3 or min hr First order rate equation dN dt k N F k rate constant with a value depending on the nucleus Integrated rate equation ln NN kt Reaction rate is 0 independent of the N0 initial N at time t concentration ofN Detecting Radiation Geiger Counter Counting the number of disintegrations per second dps or disintegrations per minute dpm for elements emitting or or 3 particles both charged space filled with a suitable gas eg Argon Pulse of electric current voltage wire at about 1000 volts relative to the tube 9 Nuclear Reactions Kinetics N decaying nuclei dN dt change in nuclei per 3 ln countss 1 counts per 3 or min hr Integrated rate equation In NNO kt time Rates Are Often Given as Halflives Halflife time required for onehalf of nuclei to decay nNNokt In12oNQIn12 n2 kn2lt12 ort12n2lk The Nuclear Halflife Halflives vary dramatically 31H t12 1226 y 1460 t12 5730 y 6027CO t12 53 y 23994Pu t12 24 x 104 y 26310689 t12 08 S Question 3 How long will a 6000 source be useful if it can be used until the vrays it produces reach 70 Eercent of the original intensity 602700 decays with a half life of 530 years to produce 6028Ni 1 Calculate k from halflife 2 Use the integrated form of the rate equation to find t Question 3 How long will a 6000 source be useful if it can be used until the vrays it produces reach 70 Eercent of the original intensity 602700 decays with a half life of 530 years to produce 6028Ni 1 Calculate k from halflife 2 Use the integrated form of the rate equation to find t knzt1m n0UNQkt Question 3 How long will a 6000 source be useful if it can be used until the vrays it produces reach 70 Eercent of the original intensity 602700 decays with a half life of 530 years to produce 6028Ni 1 Calculate k from halflife 2 Use the integrated form of the rate equation to find t k In 2 t12 0693 I 530 y 0131 V1 In NNo kt gt t In NN0 k In 70100 0131y 272 y In upper atmosphere 14 1 14 1 7N on GC quot39 1P keeps 14C12C ratio constant Plants and animals take in 12CO2 and 14CO2 Once a plant or animal dies its ratio of 14Cl12C goes down 146C 147N B t12 5730 y 1 C Dating Number Initial Number of of nuclei number halflives at time t of nuclei n M 9 60 X After 1st 90 halflife 5730 yr After 2nd halflife 11460 yr YMO 7 After 3rd halfI39fe 17190 r MO J I i v r 0 I I I I 10000 20000 Time yr Nhglx 39hm39coill fiquczIrqusI Pulyncs n gulluw Irrmiuimu likamuarcriiiiir erirri main or I luk39nmu 1 9d Ezypl 222m Igt392I 4mm 39de Imamship tomb arScsoxui iii Egypr 3730 39 rcoal rarlict IIII ui Slonchcngc Lalr Nmirniir armzi mm w 5 wulcmcnl in japan 4302 410 CVprEiS beam lamb nrsiirrcrri in Egypr 4575 unch rm from rrupriuri rhar rmrui 1crLakgOrcgon 3945 11m Ruuf Ix In ham new in xippm In u lt39Ix139un llnmmumbi 3744 um mime I Iwh Human hair Imm is Period ngi 5707 22 Land mii shells Imm Xcolhhic vilL gt of Jzu m i Iraq anI MD 0mm Indian mumuuu Icvcl 7n liarbcau Crl d Rock sham lllinok 9mm A35 IIurImi Imn bong amimri irii Folsom Man ound at Lubbock TIan 853 450 Burned bones of dam hoist in 395th mar Swain a Magdlan Chilr zl mullltm up or 0th Amerira 10360 61 MmhIIumroIirhir ransi on me MI 2m 1m 5515 900 Charruxl rmquot Luarrx Caves France sim or cxlunm c cave paintings I I I i l I I II 2000 4000 woo woo mooo 12000 H000 lama I Age years Plot of carbon 14 decay rate in counts per minute per gram of carbon Irom the sample against the age of the sample in years Buddy Question 4 What percent of the original 14C remains in the heartwood of a bristle cone pine that is 3000 y old 146C gt 147N 046 t12 5730 y nNolNkt Inxy yeX Inzkt1m Buddy Question 4 What percent of the original 1 C remains in the he rtwood of a bristle cone pine that is 3 00 old nNNo nxy yeX n2kt12 Buddy Question 4 What percent of the original 14C remains in the heartwood of a bristle cone pine that is 3000 2 old 1460 gt 1 W 016 t125730y nNNokt lnxy Xey n2kt12 gt knzt1l2 N N0 e kt e 3000 y In 25730 y e 0363 0695 695 Nuclear Power Station Generating Electricity Nuclear h r U a 8 iiiHJ iW e em Era mmmmmmsmmmmm mapWm Wm MEWS mm W mm Generating Electricity Combustion 39 i 39 mums i 7 astMran mum JWHCMVAAD ciacuurmu 39 739 pun quot r gm 5 6 age wci gt lt can ms an on Is mam 10 ms smu mm mm mi quotmam wmcu srms ms mum mum mouuczs mcmcm Artificial Nuclear Reactions Fission Neutron capture Fusion Nuclear reaction fission ENERGY 235 92 U 236 U Flselonable 92 nucleus Unstable 141 intermediate 55 Ba Fission products Nuclear Reactions Fission Production of lighter nuclei by the decomposition of a heavier nucleus Often but not always occurs when a heavier nucleus captures a neutron One of many examples in a nuclear reactor 235 1 87 146 1 Manufacture of tritium 639 1 4 3 3LI On gt 2He1H Nuclear Reactions Neutron Capture Neutron capture by a nucleus gives a heavier isotope with a one unit greater mass number Stable plutonium forms in a series of reactions several of which involve neutron capture 23892U 10 gt 23992U 23992U gt 23993Np 0 16 23993Np gt 23994Pu 0 16 23994Pu 10 gt 24094Pu 24094Pu 10 24194Pu Question 5 Is energy produced or required in this nuclear reac on 1 1 2 1H on 1H 11H 1007825 amu 21H 201410 amu 10n 1008665 amu c 300 x108 ms Question 5 Is energy produced or required in this nuclear reac on 11H 10n 21H For one mol 11H 1007825 9 21H 201410 9 10n 1008665 9 c 300 x108 ms Question 5 11H 10n 21H Am 201410 9 1007825 9 1008665 9 000239 9 per mol AE Am x c2 000239 gmol x 1 kg10009 x 300 x108 ms2 215 x1011 kg m2 2 215x1011Jmo A lot of energy is produced Nuclear Reactions Fusion Production of a heavier nucleus by combination of lighter nuclei 2 3 4 1 1H1H gt 2He On Deuterium Helium o 9 Q 39 quot 9 Energy Tritium Neutron Mu HWJr EiL quotLlE l Nuclear fusion is the energyproducing process which takes place continuously in the sun and stars In the core of the sun at temperatures of 1015 million K hydrogen is converted to helium providing enough energy to sustain life on earth Why doesn t heavy water fuse Why doesn t the heavy water in the ocean undergo spontaneous fusion 21H 21H gt 42He 402820 amu 400260 amu Low collision frequency Huge activation energy T m 10000000 K required to ignite deuterium fusion Summary Radioactive decay follows 1St order kinetics Decay rate is characterized by halflife The BE per nucleon provides a guide to predicting whether fusion or fission will occur

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