Ch. 14 & 21 nuclear chem. & kinetics test 85 points AP chem

**Academic Honesty**: The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus. I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam. If you violate any of the preceding items or do not sign, your semester grade is a F.

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For problems involving calculations, show your work in an organized manner, include any relevant equation (or formula and conversion factor(s)), put the proper units in your calculations / answer, and have the proper number of significant figures in your answer.

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1. A sample containing 2.5 * 10^{15} radioactive isotope has a radioactivity of 25 μCi; Ci = 3.7 * 10^{10} disintegration / second. [10 points]

a. what is the decay constant of this isotope ?

b. what is the half-life of the isotope ?

2. fill-in the blank for the following hypothetical nuclear reactions. [10 points]

a. ^{81}Rb undergoing electron capture: ______________________

b. alpha decay of ^{122}Sn: ______________________________

c. ^{190}W à ^{90}Sr + ____ & type of reaction = ____________

3. A sample containing a hypothetical radioactive isotope with a half-life of 225 years currently has 375 mg, while there was originally 1.2 g. What is the “age” of the sample ? [10 points]

4. It took 25.0 years for a hypothetical radioactive isotope to decay from 275 Bq to 125 Bq. What is the half-life of the isotope ? [10 points]

5. Describe the graphical analysis to determine the activation energy of a reaction; include the basis / rationale of your analysis. [10 points]

6. Describe the graphical analysis to determine if a reaction: A + B à AB

is 0^{th}, 1^{st}, or 2^{nd} order with respect to A and briefly describe the necessary experimental condition(s). [hint: your kinetics lab; 15 points]

7. Determine the rate law for the synthesis of ammonia from hydrogen and nitrogen based on the following hypothetical experimental data; include the value & units of the rate constant. [20 points]

expt |
[N |
[H |
Initial (mM / s) |

1 |
2.0 |
1.0 |
1.0 |

2 |
2.0 |
4.0 |
2.0 |

3 |
3.0 |
9.0 |
4.5 |