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