key for Exam II - SP10 - Version A - michel

# key for Exam II - SP10 - Version A - michel - 1 CHEMISTRY...

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2 1. The decomposition of dinitrogen pentoxide: 2 N 2 O 5 ( g ) 4 NO 2 ( g ) + O 2 ( g ), was monitored at 50 o C. The results are shown below. Use this data to answer the questions that follow on the next page. [N 2 O 5 ] vs time 0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.0 10.0 20.0 30.0 40.0 50.0 60.0 time, hr [N 2 O 5 ], M ln[N 2 O 5 ] vs time -3.500 -3.000 -2.500 -2.000 -1.500 -1.000 -0.500 0.000 0.0 10.0 20.0 30.0 40.0 50.0 60.0 time, hr ln[N ] target
3 (a) The rate law for the reaction is: (circle your answer): [2] Rate = – t ] O N [ 5 2 Rate = k[N 2 O 5 ] Rate = k[N 2 O 5 ] 2 k = 2 5 2 2 4 2 ] O N [ ] O [ ] NO [ (b) What is the instantaneous rate of decomposition of N 2 O 5 at 24.0 hours? Show your work clearly. [4] 1) can solve from slope of target from graph 1, or 2) rate = k[N 2 O 5 ] 24 hr = .43hr -1 *0.18M = .0078Mhr -1 (see part e for calculation of k) rate = (-1/2)*( Δ [N 2 O 5 ]/ Δ t), so Δ [N 2 O 5 ]/ Δ t = -2 * rate = -0.016Mhr -1 (c) What is the instantaneous rate of formation of NO 2 at 24.0 hours? [3] rate=(1/4)* ( Δ [NO 2 ]/ Δ t);  Δ [NO 2 ]/ Δ t = 4*0.078Mhr -1  = 0.031Mhr -1 (d) What is the approximate half life of the reaction (to the nearest hour)? [3] t [ ] t 1/2  = 16hr                                              from graph

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key for Exam II - SP10 - Version A - michel - 1 CHEMISTRY...

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