Ch. 19  nuclear chem test                                45 points                                                          chem

Show your work in an organized manner, including equation / formula, proper conversion factor(s), equation or formula, and units in your work / answer and the proper number of significant figures in your answer.

1. Write the nuclear equation describing the following (hypothetical ?) nuclear reactions.  (10 points)

a.  Alpha decay of 235-thorium:  _________________________________

b.  Positron emission from 81-selinium:  ______________________________

c. 241U undergoes spontaneous fission to form 135Cs and ?:  _________________

2.  A sample currently contains 25 mmoles of a (hypothetical ?) radioactive isotope with a half-life of 125 years, which originally contained 75 mmoles of this isotope.  Based on the preceding information, what is the “age” of the sample ?  (10 points)

3.  What does the equation, E = m c2, mean ?  [5 points]


4. Sketch / label a graph of the number of radioactive isotopes versus time to illustrate the concept of half-life.  [10 points]

 

5. If it takes 5.0 years for a (hypothetical) radioactive isotope to decay to 5.0 mg from 25 mg, what is the isotope’s ___.  [10 points]

a. decay constant

b. half-life