Everyday, reactions in the world, our bodies, and chemistry labs let off energy. A chemical reaction is one in which one or more reactants transform into different products. These reactions are primarily characterized by the breaking of bonds in products and the formation of bonds in products. Then nuclear reactions (fission, fusion) emit their energy by splitting large nuclei or combining small nuclei. They are not affected by temperature, pressure, or catalysts. In comparison, chemical reactions try to attain stability through sharing or losing electrons whereas nuclear reactions reach stability through changes.
When there is a chemical change only the outer electrons are affected, but during a nuclear process there are changes amongst the protons and neutrons contained in a nucleus. The energy between these two particles is far greater than the chemical binding between atoms. Extra energy exists as the form of binding energy necessary to hold a nucleus together. However, when the nucleus splits the "excess" energy is released in a flash. Now in order to calculate how much energy is released when nuclei split during nuclear fission the equation E=MC2 is used . Einsteins’s equation exemplifys that mass (m) can be converted to energy (e) and that the conversion factor is a huge number c (the velocity of light). One can calculate that the total mass of the fission products remaining at the end of the reaction is slightly less than the mass from the beginning.
The discovery of these results essentially led to a scientific revelation. Since nuclear reactions are more powerful than chemical reactions, they release much more energy too. Scientists were eager to manipulate the energy of uranium nuclei as an efficient power source. This is why a single fission bomb has the ability to destroy an entire city, as exemplified by the atomic bomb of the 1900’s.