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Final - CHEMISTRY 13 FINAL EXAM May 1 2006 FORM A-1 14C is...

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CHEMISTRY 13 FINAL EXAM May 1, 2006 FORM A ---------------------------------------------------------------------------------------------- 1. 14 C is produced continuously in the upper atmosphere as nitrogen atoms capture cosmic-ray neutrons. The 14 C atoms react with oxygen molecules to form 14 CO 2 , and the 14 CO 2 is assimilated by photosynthesis in plants. 14 C has a half-life of 5500 years. If the 14 C in a freshly cut twig gives 16 counts per second of β - radiation, how many counts per second will it give after 11000 years? A. 8 counts per sec B. 32 counts per sec C. 3.23 counts per sec D. 2 counts per sec E. 4 counts per sec ------------------------------------------------------------------------------------------------- 2. One of the fusion reactions in the sun’s interior is shown below. 2 1 H Æ 2 H + X What is X? A. alpha particle B. beta particle C. neutron D. positron E. gamma emission ------------------------------------------------------------------------------------------------ 3. What is the mass defect for the following radioactive decay? 14 N + 1 n 14 C + 1 p The mass of 14 N = 14.003074 amu and 14 C = 14.003241amu --------------------------------------------------------------------------------------------------
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4. Consider the following reaction: 2 NO(g) + 2H 2 (g) N 2 (g) + 2H 2 O(g) The rate law for this reaction is first order in H 2 and second order in NO. What would happen to the rate if the initial concentration of NO tripled while all other factors stayed the same? ------------------------------------------------------------------------------------------------- 5. The mechanism for the gas phase reaction is given below: H 2 + I 2 Æ 2 HI I 2 2 I (fast equilibrium) I + H 2 H 2 I (fast equilibrium) H 2 I + I Æ 2 HI (slow) What are the reaction intermediates in the mechanism? A. H 2 I and HI B. I and H 2 C. I and H 2 I D. I and HI E. There are no intermediates. ------------------------------------------------------------------------------------------------- 6. The rate constant of a reaction is tripled when the temperature is increased from 298 K to 308 K. The activation energy, E a , is -------------------------------------------------------------------------------------------------
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7. The following mechanism has been proposed for the reaction between CO and H 2 to form formaldehyde, H 2 CO: H 2 2 H (fast equilibrium) H + CO Æ HCO (slow) H + HCO Æ H 2 CO (fast) The rate law for this reaction is: A. Rate = k [H 2 ] [CO] B. Rate = k [H 2 ] 1/2 [CO] C. Rate = k [H 2 ] 2 [CO] D. Rate = k [H 2 ] [CO] 2 E. Rate = k [H 2 ] [CO] 1/2 -----------------------------------------------------------------------------------------------
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