How much energy is lost or gained when 1 mol of cobalt-60 undergoes beta-decay,

Question

How much energy is lost or gained when 1 mol of cobalt-60 undergoes beta-decay, 60/27Co -> 60/28Ni + 0/-1e? The mass of a 60/27Co atom is 59.933819 amu, and that of a 60/28Ni atom is 59.930788. * the mass of an electron is 5.4858x10-4. ---- > In the textbook, they subtract the mass of the electrons from the atoms to get the mass of the nucleus. They then use the mass of each nucleus and the mass of an electron to find delta m. I do not understand why they have to subtract the electrons from the cobalt and nickel atoms?

Explanation / Answer

First just substract the total mass of products from total mass of reactants,

Mass change = 59.933819 - 59.930788 - 0.00054858

mass change = 0.00248242 = 0.00248242 * 1.6606*10-27 kg = 4.1223*10-30 kg

Energy, E = m c2 = 4.1223*10-30*(2.9979*108)2 = 3.7049*10-13 J

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