What do you mean by Q values of Nuclear Reactions?

For the complete equation of nuclear reaction, it must include the change in energy of the reaction also. The energy change in the nuclear reaction is represented by Q. Hence the Rutherford’s Transmutation reaction would be mentioned completely as follows:

7N14 + 2He4 ——-> 8O17 + 1H1 + Q

Where Q is known as Nuclear reaction energy.

The value of Q depends on the type of reaction. If the reaction is exoergic i.e. Energy is released then the value of Q will be positive. On the other hand if the reaction is endoergic i.e. Energy is absorbed then the value of Q will be negative.

The value of Q can be calculated from the masses of the products and reactants of the equation.

Hence
Sum of the masses of reactants = 14.0031 + 4.0026 = 18.0057 a.m.u.
Sum of the masses of products = 16.9991 + 1.0078 = 18.0069 a.m.u.
Therefore, ΔM = Sum of the masses of products – Sum of the masses of reactants = 18.0069 – 18.0057 = + 0.002 a.m.u.

As the above reaction involves increase of mass by 0.002 a.m.u. hence equivalent amount of energy is being absorbed. Therefore the value of Q is negative as the reaction is endoergic.

Since
1 a.m.u. Ξ 931.5 MeV of energy
Therefore, Q=-0.0012 a.m.u. x 931.5 MeV/a.m.u. = -1.118 MeV

Hence the reaction is endoergic.

Category: Nuclear And Radiation Chemistry

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