Question

Carbon-14 decays as follows:

_{14 0            14}

                              C   ----> e   + N   

^{6 -1              7}

   isotopic masses are 14.00307 for nitrogen-14 and 14.00324 for carbon-14. What energy change (kJ/moles) occurs in the beta decay of C-14? NOTE: Do I use these two masses to get the mass defect or do I use the mass of protons and nuetrons to find the mass defect of each one and then subtract the two?

Answer 1

mass defect = mass of product - mass of reactant

                     = (14.00307 + 0.000548579 ) - 14.00324

                     = 0.0003785799 amu

1 amu =1.66053892 × 10^-27 kilograms

mass defect in Kg = = 0.0003785799 x 1.66053892 × 10^-27 = 6.286 x 10^-31 kilograms

binding energy = mass defect    x C^2

                        = 6.286 x 10^-31 x (3 x10^8)^2

                        = 5.6576 x 10^-14 J

                        = 5.6576 x 10^-17 kJ           ( divide by avagadro number = 6.023 x10^23 )

                        = 3.40 x 10^10 kJ /mol