t3b - Wednesday 1:05 p.m 1:55 p.m T est#3B 3.091 Fall Term...

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3.091 Fall Term 2004 Test #3B Wednesday, November 17, 2004 1:05 p.m. - 1:55 p.m. N a m e : (please print in UPPER CASE) Recitation Instructor: A complete test consists of 4 questions. Write your answers on these pages. State your assumptions and show calculations that support your conclusions. RESOURCES PERMITTED: PERIODIC TABLE OF THE ELEMENTS, TABLE OF CONSTANTS, AN AID SHEET (ONE PAGE 8½" × 11"), AND A CALCULATOR. NO BOOKS OR OTHER NOTES ALLOWED. USE OF WIRELESS COMMUNICATIONS DEVICES STRICTLY FORBIDDEN. #1 24% #2 28% #3 28% #4 20% TOTAL 100%

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3.091 Fall Term 2004 Test #3B page 2 Problem #1 (24%) log 10 (rate) inhibited reaction slope, n = 1 intercept, k = 3.091 log 10 (concentration) The fictitious compound, administratium sulfide (Ad 2 S), decomposes readily at temperatures exceeding 365ºC. The figure above shows the kinetics of the reaction conducted at 400ºC. The reaction is first order in concentration of Ad 2 S. The value of the specific chemical rate constant, k , is 3.091 s –1 . 4% (a) On the graph above, label the slope and the intercept, indicating the numerical value of each. (b) Calculate how long it takes at 400ºC for the concentration of Ad 2 S to fall from 2.22 mole L –1 to 10% of that value. Express your answer in seconds. 14% (c) The same reaction is now conducted under the influence of an inhibitor. On the graph above, which shows the reaction as it proceeds in the absence of an inhibitor, draw the line associated with the inhibited reaction. 6%
3.091 Fall Term 2004 Test #3B page 3 Problem #2 (28%) Composition A: 25% Li 2 O – 75% B 2 O 3 ; Composition B: 5% Li 2 O – 95% B 2 O 3 (a) Two glass-forming melts, A and B as specified above, are each cooled at the same rate down to room temperature. Identify which melt, A or B, exhibits the higher glass transition temperature and explain why. 8%

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t3b - Wednesday 1:05 p.m 1:55 p.m T est#3B 3.091 Fall Term...

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