Is nuclear fusion endothermic or exothermic?

Answer 1

Nuclear fusion can be either exothermic or endothermic. We're most familiar with the exothermic kind. Fusion in stars releases immense quantities of energy. A fusion nuclear weapon releases enormous energy. But there are situations where fusion is endothermic. We don't usually think of them because of the subtle way they occur. You're wondering what's up, and the answer is in the stars. When a star burns all its energy fusing atoms together, it "hits the wall" at iron. Iron making is the last of the exothermic nuclear fusion reactions. But in stars that have sufficent mass and makeup, those that go supernova, endothermic nuclear fusion is the mechanism by which all the elements heavier than iron are created. It's the only way that they can be created in nature. When the star collapses and that tipping point where the exothermic fusion reactions can't hold it up against its own massive gravity, then it's "go time" and endothermic fusion can occur. The "big squeeze" put on all the matter creates gigantic amounts of heat - enough to drive endothermic fusion. Then the blast distributes all that material across the universe. Including the trans-iron elements created in endothermic fusion reactions during collapse and the nova event.

Answer 2

Fusion reactions that produce nuclei lighter than iron or nickel are mostly exothermic; fusion reactions producing nuclei heavier than that are almost all endothermic. Since endothermic (actually, for fusion reactions, the preferred term seems to be "endergonic") processes require energy, they're almost by definition less common than processes which release energy.

Answer 3

Most, but not all.

Most often, when we think of nuclear fusion, the process we are thinking about is exothermic. Certainly the reactions that fuse hydrogen isotopes into helium are strongly exothermic, as are all involving light atoms.

As the atoms get heavier, the amount of energy released in fusion diminishes. We finally get to fusion reactions that take place between atoms heavier than iron, and these are mostly endothermic.

Answer 4

No, fusion of atoms larger than nickel and iron are endothermic and can only occur in supernova explosions.

Also fusion of 2 helium atoms is energetically impossible and just results in various isotopes of hydrogen. To get exothermic helium fusion you need 3 helium atoms, which requires very very high temperature and pressure and produces carbon.

Answer 5

It depends on what's being produced. Fusion that produces nuclei lighter than iron generally releases energy; fusion producing nuclei heavier than that generally requires energy.

Answer 6

That depends on what atoms are being fused. For atoms lighter than nickel & iron fusion is exothermic. For atoms heavier than nickel & iron fusion is endothermic.

Answer 7

Exothermic