Nuclear Chemistry and Radioactivity Flashcards

Einstein's equation E = mc² relates mass and energy in nuclear reactions. What does 'c' represent?

Answer: The speed of light in a vacuum

In E = mc², c is the speed of light (~3 × 10⁸ m/s); because c² is enormous, even tiny mass losses produce vast amounts of energy.

Nuclear fusion requires extremely high temperatures primarily because:

Answer: High temperature provides energy to overcome the electrostatic repulsion between positively charged nuclei

Positively charged nuclei repel each other (Coulomb repulsion); extremely high kinetic energy (temperature) is needed for them to get close enough for the strong nuclear force to fuse them.

Which type of radiation is stopped most easily and cannot penetrate human skin?

Answer: Alpha particles

Alpha particles are large, heavy, and doubly charged; they lose energy quickly and are stopped by a few centimeters of air or a sheet of paper.

The nuclear binding energy of a nucleus represents:

Answer: The energy required to completely separate a nucleus into its individual protons and neutrons

Nuclear binding energy is the minimum energy needed to disassemble a nucleus into its constituent free protons and neutrons; it reflects nuclear stability.

Positron emission (beta-plus decay) results in:

Answer: A decrease in atomic number by 1

In positron emission, a proton converts to a neutron, so the atomic number decreases by 1 while the mass number stays the same.

Which factor most directly determines whether a nucleus is stable or radioactive?

Answer: The ratio of neutrons to protons in the nucleus

Nuclear stability is primarily governed by the neutron-to-proton (n/p) ratio; nuclei with ratios too high or too low tend to be radioactive.

In the nuclear equation ²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ?₃₆Kr + 3¹₀n, what is the mass number of the krypton product?

Answer: 92

Mass numbers must balance: 235 + 1 = 141 + ? + 3(1), so ? = 236 − 141 − 3 = 92; the krypton isotope has mass number 92.