1. Energy: Nuclear reactions involve changes in the nucleus of an atom, and these changes can release enormous amounts of energy, as seen in nuclear power plants and atomic bombs. This energy can take various forms, including heat, light, and radiation.

2. New elements: Nuclear reactions can alter the composition of the nucleus, leading to the formation of new elements. This is the basis of nuclear fusion, where lighter elements fuse together to form heavier elements, releasing energy in the process. Examples include the creation of helium from hydrogen in the sun and the formation of heavier elements in supernova explosions.