Example
Consider the nuclear fission of 236U into 92Kr, 141Ba, and three neutrons.
236U → 92Kr + 141Ba + 3 n
The mass number of 236U is 236. Because the actual mass is u, the mass excess is u. Calculated in the same manner, the mass excess for 92Kr, 141Ba, and a neutron are u, u and u, respectively. The mass excess of the reactant is u, and the mass excess of the products is The difference between reactants and products is u, which shows that the mass excess of the products is less than that of the reactants, and so the fission can occur – a calculation which could have been done also with only the masses of the reactants.
The resulting difference in mass (excess) can be converted into energy using 1 u = 931.494 MeV/c², yielding 166 MeV.
Read more about this topic: Mass Excess
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