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Chapter: 11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes

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Difference between chemical reactions and nuclear reactions

In ordinary chemical reactions, the nuclei of the atoms taking part in a chemical reaction remain unaffected. Only the electrons in the extranuclear part of atoms take part in the chemical process.


Difference between chemical reactions and nuclear reactions


In ordinary chemical reactions, the nuclei of the atoms taking part in a  chemical reaction remain unaffected. Only the electrons in the extranuclear part of atoms take part in the chemical process.

However, during disintegration of atoms (naturally or artificially), the nuclei of atoms are affected resulting in the formation of new nuclei. Such reactions in which the nuclei of the atoms interact with other nuclei or lighter particles or photons resulting in the formation of new nuclei and one or more lighter particles are called nuclear reactions.

 

Chemical reactions

1.     These reaction involve some loss, gain or overlap of outer orbital electrons of the reactant atoms.

2.     A chemical reaction is balanced in terms of mass only

3.     The energy changes in any chemical reaction is very much less when compared with nuclear reaction.

4.     In chemical reactions, the energy is expressed in terms of kilojoules per mole.

5.     No new element is produced since nucleus is unaffected.

 

Nuclear reactions

1.     Nuclear reactions involve emission of alpha, beta and gamma particles from the nucleus.

2.     Nuclear reaction is balanced in terms of both mass and energy.

3.     The energy changes are far exceed than the energy changes in chemical reactions.

4.     In nuclear reactions, the energy involved is expressed in MeV (Million electron volts) per individual nucleus.

New element / isotope may be produced during the nuclear reaction.



The following facts are taken into account while expressing a nuclear reaction:

 

       i.            Reactions are written like a chemical equation. Reactants are written on the left hand side and products on the right hand side with an arrow in between.

     ii.            Mass number is written as super script on the symbol of the element. For example 7N14 stands for an atom of nitrogen with mass number 14 and atomic number 7.

    iii.            In a chemical reaction the total number of atoms of various elements are balanced on the two sides. Similarly in nuclear reaction , the total mass number and atomic number are balanced on the two sides.

  iv.            Symbols used for projectiles:

The bombarding particles are called projectiles. These projectiles are represented by the following symbols.

0n1   - neutron

1H1or p  -  proton

2H4  -  proton

1H2or D2  -  proton

1e0 or e - electron or β-particle

+1e0 - positron

The nucleus to be attacked is called as target nucleus or parent. The new nuclide is called as recoil nucleus or daughter. The particle ejected during a nuclear reaction is called as ejected particle.

7N14 + 2He4  -- > 8O17 + 1H1

This reaction can be represented as (a, p) type reaction .Hence the above reaction is represented as 7N14 (a,p) 8O17.

 

Q value of a nuclear reaction

The amount of energy absorbed or released during nuclear reaction is called

Q-value of nuclear reaction.

Qvalue  =   (mp-mr) 931 MeV

where    mr   - Sum of the masses of reactants

mp   - Sum of the masses of products

In the case of energy absorbed then mp>mr, then Q value will be positive. Q value of a nuclear reaction in the case of energy released = (mp-mr) 931 MeV. In the case of energy released, mr>mp, and hence Q value will be negative.


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