# 19.E: Nuclear Chemistry

### Q19.1

Balance each of the following nuclear equations and indicate the type of nuclear reaction ($$\alpha$$-emission, $$\beta$$-emission, fission, fusion, or “other”).

1. $$\mathrm{\ce{^{239}_{94}Pu}+\ce{^1_0n}\rightarrow \ce{^{130}_{50}Sn}+{?}+3^1_0n}$$
2. $$\mathrm{{?} + \ce{^{6}_{3}Li} \rightarrow 2^4_2He}$$
3. $$\mathrm{\ce{^{210}_{84}Po}\rightarrow \ce{^4_2He}}+{?}$$
4. $$\mathrm{\ce{^{235}_{92}U}+{^1_0n}\rightarrow \ce{^{72}_{30}?}+{?}+4^1_0n}$$
5. $$\mathrm{\ce{^{125}_{53}I}\rightarrow \ce{^{125}_{53}I}+{?}}$$
6. $$\mathrm{\ce{^{238}_{92}U}\rightarrow {?}+\ce{^{234}_{?}Th}}$$
7. $$\mathrm{\ce{^{235}_{92}U}+{^1_0n}\rightarrow \ce{^{86}_{?}Br}+\ce{^{147}_{?}?}+{?^1_0n}}$$
8. $$\mathrm{\ce{^{234}_{90}Th}\rightarrow {?}+\ce{^{234}_{91}?}}$$

### Q19.2

The isotope $$\ce{^{137}_{55}Cs}$$ undergoes beta emission with a half-life of 30 years.

1. Write a balanced nuclear equation for this reaction.
2. What fraction of $$\textrm{Cs-137}$$ remains in a sample of the isotope after 60 years?
3. What mass of $$\textrm{Cs}$$ will be left in a 24.0 g sample of $$\ce{^{137}_{55}Cs}$$ after 90 years?
4. What fraction of $$\textrm{Cs-137}$$ has decayed after 120 years?

### Q19.3

What is the half-life of an isotope that is 75% decayed after 16 days?

### Q19.4

Explain what makes an isotope radioactive. Why do radioactive isotopes undergo radioactive decay?  How does the energy released by nuclear reactions compare to that released by ordinary chemical reactions?  Why?

### Q19.5

Write balanced nuclear equations for:

1. positron emission by $$\textrm{Sr-83}$$
2. the fusion of two $$\textrm{C-12}$$ nuclei to give another nucleus and a neutron.
3. the fission of $$\textrm{U-235}$$ to give $$\textrm{Ba-140}$$, another nucleus and an excess of two neutrons.

### Q19.6

What new element is formed when $$\textrm{K-40}$$ decays by $$\beta$$-emission?  Is the new element formed likely to be stable?  Why or why not?

### Q19.7

Why is nuclear fission considered a “chain reaction”?  What is “critical” about critical mass? Why does nuclear fission produce radioactive waste?