Nuclear Fusion

Nuclear fusion occurs when  two or more light and small nuclei come together to perform a heavier nucleus.
This process is accompanied by the release of a huge amount of energy.

For example

Deuterium + Tritium = Helium + neutron + (Energy)
(2H1) + (3H1) = (4He2) + (1n0) + Energy



It is far more difficult to achieve fusion than fission due to the nature of the hydrogen nuclei that repel each other. In order to let this happen, the nuclei should be heated up to 10^8 K or more so that the nuclei will have enough kinetic energy to overcome the electrical repulsion between the nuclei.

The Sun acquires its energy from the fusion of hydrogen nuclei.

- Deuterium clashes with tritium to form a helium nucleus at a high temperature. This is accompanied by the release of a neutron and mass defect. The mass defect produces a massive amount of energy.

A hydrogen bomb also uses the principle of nuclear fusion for its design.

Nuclear Fission

Nuclear fission is a process involving the splitting of heavy nucleus into two or more nuclei of roughly equal mass with the release of several neutrons at the same time.

Nuclear fission seldom occurs spontaneously. Usually it occurs when the heavy nucleus is bombarded by a neutron.

Induced fission occurs when reaction caused by neutrons absorption.

Spontaneous fission occurs when nuclei undergo fission without initial neutron absorption.

The reaction causes large mass defect which appears mostly as kinetic energy of the fission fragments. They fly apart at great speed and colliding with the atoms in the vicinity and increasing their average kinetic energy. This causes them to have higher temperature and give out heat. Thus, nuclear fission is one of the source of heat energy.

Example of nuclear fission are:

Source: http://www.green-planet-solar-energy.com/images/nuclear_fission_good_1a.jpg




Source: chem-guide.blogspot.com