A hypothetical atom with negligible kinetic energy has a mass of 216 amu. It undergoes an alpha decay. The remaining atom has atomic mass 211.994 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 216 amu - ( 211.994 amu + 4.001 amu) = 4.99677E-03 amu, or about 8.29463E-03 * 10^-27 kg.
This corresponds to an energy of E = m c^2 = 8.29463E-03 * 10^-27 kg ( 3 * 10^8 m/s) ^ 2 = 4.49709 * 10^-13 Joules.
A mole of these nuclei would constitute 6.02 * 10^23 nuclei, each releasing 4.49709 * 10^-13 Joules. The total energy released would therefore be