hw12solution_pdf

# 1 2 4 ms 2 not enough information is given 3 3 5 ms 4

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1. 2 . 4 ms 2. Not enough information is given. 3. 3 . 5 ms 4. 1 . 8 ms correct Explanation: t 1 / 2 = [BaCO 3 ] 2 K = 1 2 (2 . 85 × 10 2 ) = 1 . 8 ms 028 3.3points The initial concentration of the reactant A in a first-order reaction is 1.2 M. After 69.3 s, the concentration has fallen to 0.3 M. What is the rate constant k ? (ln 2 = 0 . 693) 1. 0 . 02 s 1 correct 2. 0 . 2 s 1 3. 0 . 01 s 1 4. not enough information Explanation: t 1 / 2 = 69 . 3 s 2 = 34 . 7 s k = ln 2 t 1 / 2 = 0 . 693 34 . 7 s = 0 . 02 s 1

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casey (rmc2555) – Homework 12 – holcombe – (51395) 9 029 3.3points Consider the first order reaction A products where 25% of A disappears in 24 seconds. What is the half life of this reaction? 1. t 1 / 2 = 48 s 2. t 1 / 2 = 12 s 3. t 1 / 2 = 36 s 4. t 1 / 2 = 25 s 5. t 1 / 2 = 40 s 6. t 1 / 2 = 58 s correct Explanation: a = 1 t = 24 s [A] 0 = 100 [A] t = 75 ln parenleftbigg [A] 0 [A] t parenrightbigg = akt k = 1 at ln parenleftbigg [A] 0 [A] t parenrightbigg = 1 24 s ln parenleftbigg 100 75 parenrightbigg = 1 . 199 × 10 2 s 1 t 1 / 2 = ln 2 k = 58 s 030 3.3points The decomposition of dimethylether at 504 C is first order with a half-life of 1570 sec- onds. What fraction of an initial amount of dimethylether remains after 4710 seconds? 1. 1 6 2. 1 3 3. 1 32 4. 1 8 correct 5. 1 16 Explanation: t 1 / 2 = 1570 s t = 4710 s Represent dimethylether as compound D. Elapsed time: 1570 s + 1570 s + 1570 s = 4710 s. Remaining Rxn: D/2 D/4 D/8 Sample left = 1 8
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