Chemistry: Nuclear Chemistry: Fission, Fusion, and Decay
Balancing nuclear reactions and understanding radioactive processes
Chemistry: Nuclear Chemistry: Fission, Fusion, and Decay
Balancing nuclear reactions and understanding radioactive processes
Chemistry - Grade 9-12
- 1
In alpha decay, uranium-238 becomes thorium-234 and releases an alpha particle. Write the balanced nuclear equation using isotope notation.
An alpha particle is the same as a helium-4 nucleus with atomic number 2.
The balanced nuclear equation is U-238 -> Th-234 + He-4. The mass numbers balance because 238 = 234 + 4, and the atomic numbers balance because 92 = 90 + 2. - 2
Carbon-14 undergoes beta-minus decay to form nitrogen-14. Write the balanced nuclear equation and explain what happens to the atomic number.
The balanced nuclear equation is C-14 -> N-14 + beta particle. In beta-minus decay, the mass number stays the same and the atomic number increases by 1, changing carbon with atomic number 6 into nitrogen with atomic number 7. - 3
A radioactive isotope has a half-life of 8 days. If a sample starts with 80 grams, how many grams remain after 24 days?
Divide the mass by 2 once for each half-life.
After 24 days, 10 grams remain. Since 24 days is 3 half-lives, the sample changes from 80 grams to 40 grams to 20 grams to 10 grams. - 4
Compare nuclear fission and nuclear fusion in terms of what happens to atomic nuclei.
Nuclear fission is the splitting of a large nucleus into smaller nuclei, often releasing neutrons and energy. Nuclear fusion is the combining of small nuclei into a larger nucleus, also releasing energy. - 5
Complete and balance this nuclear equation: U-235 + n-1 -> Ba-141 + Kr-92 + ___ n-1.
Add the mass numbers on both sides of the equation.
The missing coefficient is 3, so the equation is U-235 + n-1 -> Ba-141 + Kr-92 + 3 n-1. The mass numbers balance because 235 + 1 = 141 + 92 + 3. - 6
A nucleus emits a gamma ray. Describe how the mass number and atomic number of the nucleus change.
The mass number and atomic number do not change during gamma emission. Gamma radiation is high-energy electromagnetic radiation released when the nucleus loses energy. - 7
Radium-226 decays by alpha emission. Identify the daughter isotope by mass number and element name.
Subtract 4 from the mass number and 2 from the atomic number.
The daughter isotope is radon-222. Alpha decay lowers the mass number by 4 and the atomic number by 2, so radium-226 with atomic number 88 becomes radon-222 with atomic number 86. - 8
A 200 gram sample of iodine-131 decays to 25 grams in 24 days. How many half-lives have passed, and what is the half-life of iodine-131 in this situation?
Three half-lives have passed because 200 grams becomes 100 grams, then 50 grams, then 25 grams. The half-life is 8 days because 24 days divided by 3 half-lives equals 8 days per half-life. - 9
Explain why a nuclear chain reaction can occur during fission of uranium-235.
Focus on the role of neutrons released during each fission event.
A nuclear chain reaction can occur because fission of uranium-235 releases neutrons. Those neutrons can strike other uranium-235 nuclei, causing more fission reactions and releasing more neutrons. - 10
Hydrogen isotopes can fuse in stars to form helium. Explain why fusion requires extremely high temperature and pressure.
Fusion requires extremely high temperature and pressure because positively charged nuclei repel each other. High temperature and pressure give the nuclei enough energy and collisions to get very close and combine. - 11
Identify the type of decay represented by this change: P-32 -> S-32 + beta particle.
In beta-minus decay, a neutron changes into a proton and an electron is emitted.
This is beta-minus decay. The mass number stays 32, and the atomic number increases from 15 for phosphorus to 16 for sulfur. - 12
A medical tracer has a half-life of 6 hours. A patient receives a dose with an activity of 64 units. How much activity remains after 18 hours?
Count how many 6 hour half-lives fit into 18 hours.
After 18 hours, 8 units of activity remain. Since 18 hours is 3 half-lives, the activity changes from 64 units to 32 units to 16 units to 8 units.