Balancing Nuclear Equations and Half-life Calculations
Determine “X” in reactions 1-5 below.
1.
212
84 Po
 82208Pb + X
2. Cs-137  Ba-137 + X
3. As-78  - + X
4.
4
9
Be +   C-12 + X
5. K-38  Ar-38 + X
Half-life
6. The half-life of plutonium-239 is 24,110 years. If you have an original mass of 100 g, how much remains
after 96,440 years?
7. The half-life of polonium-218 is 3.0 minutes. If you start with 16 tons, how long will it be before only 1 ton
is left?
8. The half-life of thorium-227 is 18.72 days. How many days are required for three-fourths of a given amount
to decay?
9. Gold-198 has a half-life of 2.7 days. If you have an original mass of 50 g, how much will remain after 1
week?
10. Technetium-99 has a half-life of 6.0 hours. If an original mass contains 100 mg, how much will remain
after 2.0 days?
11. Calculate the half-life of an element having an original mass of 276 g and a final mass of 4.76 g after
decaying for 4.39 days.