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Nuclear Fission and Fusion - Part V

6. Difference between nuclear reactions and chemical reactions
The term reaction is used when compounds or elements convert to another form. Chemical reactions are common reactions that we encounter often. Similar to chemical reactions, nuclear reactions also take place; here nuclei transmute and change from becoming nuclei of one element to another element. But there are vast differences between chemical and nuclear reactions. Let us see what these differences are.

Whenever the term chemical reaction is used, it means converting one compound into a new one. We have seen in detail how chemical reactions occur. Compounds are formed by bonds between its constituent elements. When chemical reactions between compounds or elements take place, only the outermost electrons are rearranged. The elements remain unchanged. The energies involved are very small and the reactions can be endothermic or exothermic.

When Na atom reacts with a Cl atom, a compound NaCl is formed. The reaction is shown below.

The electrons in Na and Cl rearrange to form NaCl and a very small amount of energy is released in this reaction.

In the chemical reaction shown below, the electronic structures of the reacting chemicals rearrange to make new products.

It has to be noted that the chemical elements of the reactants and products are a conserved quantity. A Ca atom, for example, does not become another atom say a carbon C atom!!

Similar to chemical reactions, nuclear reactions also produce new products, but here a new element is made. This means that a new element with different proton and neutron numbers is formed in a nuclear reaction. These processes release a very large amount of energy. Sometimes to start nuclear reactions, the reacting nuclei have to be bombarded at very high energies; this is necessary because the nuclei have to overcome their positive electrostatic repulsion between each other.

Some examples of nuclear reactions are given below.

There are two types of nuclear reactions : nuclear fusion reactions and nuclear fission reactions. We have seen these reactions in the earlier section. All nuclear reactions are exothermic reactions and release a lot of heat and light energies.

Let us look at the differences between chemical and nuclear reactions:

In a chemical reaction, atoms undergo changes and the products are new chemicals.		In a nuclear reaction, nucleus of an atom undergoes changes and the products are new nuclei.
In a chemical reaction, electrons participate in the reaction. The nuclei are not affected.		In nuclear reactions, the nuclei undergo changes. A nuclear reaction alters the composition of the parent nuclei.
In a chemical reaction, the elements do not change. The amount of elements in the reaction and the products is conserved.		In a nuclear reaction, the identity of the element changes because the nuclei undergo changes. But the number of total nucleons is conserved in nuclear reactions.
In a chemical reaction, usually a very small amount of energy is liberated or absorbed.		In a nuclear reaction, very large amounts of energy is liberated. Endothermic nuclear reactions are not seen.
In a chemical reaction, there is no radioactivity given off.		All nuclear reactions are accompanied by strong radioactive emissions.
In a chemical reaction, all isotopes give the same chemical reactivity.		The same is not true for nuclear reactions. Each isotope can have its own reactions.
Chemical reactions are affected by changes in temperature and pressure of reacting compounds.		Nuclear reactions are not affected by temperature or pressure applied on reacting nuclei.
Chemical reactions can be reversed.		Nuclear reactions cannot be reversed. In some rare reactions the reactions can be reversed under very hard experimental conditions.

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