Question

Fusion and fission reactions are both nuclear reactions that can be used to produce energy. However, while fission reactions are observed as a natural decay route for some nuclei on Earth, fusion is not seen under typical ambient planetary conditions. More extreme conditions, like are present in stars, are typically necessary for fusion to occur on a large scale.1. Which of the answers below correctly describes the reasoning for this difference?A) Both fusion and fission reactions are initiated by neutron addition to the nuclei involved in the reaction. However, fusion reactions, unlike fission reactions, do not produce large amounts of extra neutrons to propagate the chain reaction needed to sustain a reaction at a high rate.B) Both fusion and fission reactions require nuclear collisions. Fusion reactions involve smaller nuclei which collide less frequently with each other, causing a slower reaction. Fission reactions involve larger nuclei, making collisions more frequent, leading to faster reaction rates.C) Fusion reactions result in less energy released as heat than is seen in fission reactions. Because less heat is released there is less energy present in the reactants to overcome the large activation energy for these reactions. Fission reactions also have a large activation barrier, but the heat produced by these reactions is much greater, giving the nuclei the energy they need to complete the reaction.D) Fusion reactions have a larger barrier to reaction due to the repulsion forces required for two nuclei to come together. Because the nuclei are both positively charged, the repulsive force between the two has to be overcome for fusion to occur. Fission reactions do not involve nuclear collisions and therefore have a lower barrier to reaction.E. The binding energy per nucleon is much lower, on average, for atoms involved in fusion reactions. This means that the reactions are less energetically favorable, as binding energy per nucleon is a measure of stability. Because there is much less energetic driving force, the reaction rate is much slower overall, meaning that it is more difficult to observe under ambient conditions.

Answer 1

Nuclear fission reactions can naturally occur on Earth due to the lower energy required to initiate them, whereas nuclear fusion requires extremely high temperatures and pressures to overcome the electrostatic repulsion between light nuclei, conditions that are not naturally found on Earth but are present in stars.

Step-by-step explanation:

The difference in observation of nuclear fission and nuclear fusion under Earth's conditions can be explained by the inherent properties of these reactions. Fission can occur naturally when large, unstable nuclei, like uranium-235, capture a neutron and are split into smaller nuclei, releasing energy and more neutrons. This neutron-induced chain reaction can occur at lower energies compared to fusion. In contrast, fusion requires the combination of two light nuclei, such as those of hydrogen, to form a heavier nucleus, like helium. This process is hindered by the electrostatic repulsion between the positively charged nuclei, necessitating extremely high temperatures and pressures to overcome this barrier, akin to conditions found in stars.

Fusion is more efficient and can produce more energy per reactant mass, but the activation energy is very high due to the need to overcome the Coulomb barrier, which is the repulsion between nuclear particles. The gravitational pressure in stars provides the necessary environment for fusion, but achieving this on Earth requires sophisticated technology to replicate such extreme conditions.