Nuclear versus Chemical Reactions

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There is a fundamental difference between chemical reactions (such as the burning of coal or natural gas) and nuclear reactions. Consider the chemical reaction:

CH4 + 2O2 -> CO2 + 2H2O + DE

Methane + Oxygen Carbon dioxide + Water vapor + Heat Note that after the reaction is completed, we still have one atom of carbon, four atoms of oxygen, and four atoms of hydrogen. The number of molecules, however, is not the same in a chemical reaction since atoms are rearranged to form new molecules. In this reaction, one molecule (or one mole) of methane reacts with two molecules (or two moles) of oxygen, and results in one molecule (or one mole) of carbon dioxide and two molecules (or two moles) of water. The total mass of reactants (methane and oxygen in our example) and products (in this case carbon dioxide and water vapor) also remain the same. Chemical energy appears because of the reconfiguration of atoms and the lower energies in newly created bonds, as compared to that in bonds which have been broken.

In chemical reactions, atoms are conserved - the total number of atoms of each element remains constant.

Question: Why do elements making up a chemical compound combine in definite proportions?

Answer: John Dalton, an English scientist, pointed out that all elements are made of atoms that look like billiard balls and that these atoms must bind with each other in full or not bind at all. Although the description of atoms as rigid balls is not quite right, the explanation was a great step forward in understanding the nature of atoms.

In a nuclear reaction, atoms lose their identity. For example, when uranium-235 is hit with a neutron, two lighter elements such as krypton and barium are formed and two or three neutrons are released. In this case, the total number of elementary particles (electrons, protons, and neutrons) is conserved. The mass of the product is slightly smaller than the mass of the reactants. Energy is released because the configuration of elementary particles forming the nucleus of the fragments has a lower binding energy (mass) than that of the nucleus of the atom undergoing fission.

In nuclear reactions, the total number of nucleons is conserved - the total number of neutrons and protons remains constant. Another notable distinction between chemical and nuclear reactions is the huge difference in the amount of energy each releases. This is because the binding energy that holds a nucleus together is far greater than the energy that holds electrons to a nucleus. For example, the fission of one kilogram of uranium provides as much energy as 2.4 million kilograms of the best quality coal. Even though nuclear fuel contains only 3-5% fissionable material, the tremendous energy released from a nuclear reaction is apparent.

Question: Throughout history, alchemists have tried to transform copper, mercury, and other metals into gold, only to experience disappointment. To what do you attribute the cause of their failures?

Answer: Alchemists mistakenly tried to perform this task by means of chemical reactions. As we now know, the process requires the deconstruction of the nucleus and rearrangement of the elementary particles (protons and neutrons) into new elements. This is only possible using nuclear reactions that were unknown to them at the time!


(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Bodansky, Nuclear Energy Principles, Practices, and Prospects, Second Ed., Springer, 2004.

Seaborg, G., T., Peaceful Uses of Nuclear Energy, University Press of the Pacific, 2005.

International Journal of Nuclear Engineering and Design, Direct Science Elsevier Publishing Company, devoted to the Thermal, Mechanical, Material and Structural Aspects of Nuclear Fission.

Journal of Fusion Energy, Springer Netherlands. It features articles pertinent to development of thermonuclear fusion.

External Links

Federation of American Scientists (

International Atomic Energy Agency (

DoE Office of Nuclear Energy, Science & Technology (

American Nuclear Society, (

World Association of Nuclear Operator (WANO) (