Given that the energy released in the fusion of two deuterium atoms to a 3He and a neutron is 3.3 MeV, and in the fusion to tritium and a proton it is 4.0 MeV. Calculate the energy change for the process 3He + 1n-3H + 1p. Suggest an explanation for why this process occurs at much lower temperatures than either of the first two.

Nuclear fusion is a process where two light atomic nuclei combine to form a heavier nucleus, releasing energy in the process. It's the same type of reaction that powers our Sun, providing heat and light to our solar system. In the heart of the Sun, hydrogen atoms fuse to create helium, and this process is what keeps stars burning for millions to billions of years.

For nuclear fusion to occur, conditions of extremely high temperature and pressure are necessary to overcome the repulsive forces between positively charged nuclei. When these nuclei collide with enough force, they can merge, and this fusion results in a mass difference between the reactants and the products. According to Einstein’s famous equation, E=mc^2, this mass difference is converted into energy, which can be calculated and measured in mega electronvolts (MeV).

Fusion research on Earth aims to harness this energy in a controlled way to provide a powerful and sustainable source of energy. Deuterium fusion reactions are particularly appealing because deuterium is abundant in seawater, making it a potential vast reservoir of fuel.

Deuterium, or heavy hydrogen, is a stable isotope of hydrogen containing one proton and one neutron. Fusion reactions involving deuterium are of significant interest because they can potentially yield a great deal of energy with relatively manageable reaction conditions.

In deuterium fusion, two deuterium atoms collide and fuse to either form helium-3 and a neutron or tritium and a proton, depending on the interaction specifics. The process described in the original problem presents two reactions yielding different energy outputs—3.3 MeV and 4.0 MeV. These reactions illustrate the process of converting mass into energy, where the slight loss in mass results in a significant energy release.

Each deuterium fusion reaction requires a unique set of conditions, such as temperature and pressure, to succeed. Understanding these requirements is essential for developing practical fusion reactors, as they influence the reactor's design and operational parameters.

In chemistry and physics, reactions can be broadly classified as endothermic or exothermic. Endothermic processes require an input of energy to proceed, absorbing heat from their surroundings. On the contrary, exothermic processes release energy, often in the form of heat, making the surroundings hotter.

The reactions involving deuterium fusion to create helium-3 or tritium are exothermic—they release energy as the products have less mass than the reactants. This released energy is what we seek to harness for power generation. However, the process mentioned in the original problem, the conversion of helium-3 and a neutron into tritium and a proton, is an endothermic reaction. It absorbs energy, resulting in a cooler reaction environment.

The temperature difference between endothermic and exothermic reactions is an essential factor in fusion research. For fusion to become a practical energy source, we must trigger and maintain exothermic reactions efficiently, while managing or avoiding endothermic reactions that would lower the system's overall energy output.