A hypothetical atom with negligible kinetic energy has a mass of 161 amu. It undergoes an alpha decay. The remaining atom has atomic mass 156.995 amu. What is the kinetic energy and/or wavelength (whichever is more appropriate) of the emitted particle, assuming that the kinetic energy of the remaining atom is negligible? How much energy would be released by the decay of a mole of these atoms? Note that the mass of a helium nucleus is about 4.001 amu and the mass of an electron about .00055 amu, where an amu is approximately 1.66 * 10^-27 kg.
The change in atomic mass is approximately 161 amu - ( 156.995 amu + 4.001 amu) = 4.00495E-03 amu, or about 6.64821E-03 * 10^-27 kg.
This corresponds to an energy of E = m c^2 = 6.64821E-03 * 10^-27 kg ( 3 * 10^8 m/s) ^ 2 = 3.60445 * 10^-13 Joules.
A mole of these nuclei would constitute 6.02 * 10^23 nuclei, each releasing 3.60445 * 10^-13 Joules. The total energy released would therefore be