Question

Define the terms 

(i) mass defect 

(ii) binding

energy for a nucleus and state the relation between the two. For a given nuclear reaction, the B.E. / nucleon of the product nucleus / nuclei is more than that for the original nucleus / nuclei. Is this nuclear reaction exothermic or endothermic in nature ?Justify your choice.

Answer 1

(i) Mass defect (ΔM), of any nucleus ^A_ZX  is the difference in the mass of the nucleus (= M and the sum of masses of its constituent nucleons (= M')

ΔM = M' - M

= [Z m_p + (A - Z)m_n] - M

where mo and m,, denote the mass of the proton and the neutron respectively.

(ii) Binding energy is the energy required to separate a nucleus into its constituent nucleons. The relation between the two is

B. E. = (mass defect)c²

(iii) There is a release of energy, i.e. the reaction is exothermic. 

Reason : Increase in B.E/nucleon implies that the more mass has been converted into energy. This would result in release of energy