In: Chemistry
What amount of energy, in kJ, is released when a mole of Co-57 undergoes electron capture? Recall that 1 J = 1 kgm2/s2.
mass of nucleus Co-57: 56.93629 amu
mass of nucleus Fe-57: 56.93539 amu
mass of electron: 0.000549 amu
The reaction involved is
Co-57 + e- ---------> Fe-57
Energy = (mass defect)*velocity of light
Mass defect = Mass of Fe-57 - (Mass of Co-57 + mass of electron)
= 56.93539 amu - (56.93629 amu - 0.000549 amu)
= -0.001449 amu
In units of kg, 1 amu = 1.66054 x 10-27 kg
Mass defect = -0.001449 amu * 1.66054 x 10-27 kg/amu
= - 2.4061 x 10-30 kg
velocity of light = 2.9979 x 108 m/s
Energy = mass defect * (velocity)2
= (- 2.4061 x 10-30 kg)*( 2.9979 x 108 m/s)2
= -21.624 x 10-14 kgm2/s2
= -21.624 x 10-14 J/atom
So, amount of energy released by electron capture of 1 atom of Co-57 = 2.16 x 10-10 kJ
For 1 mole of Co-57, the energy released will be 2.16 x 10-10 kJ * 6.022 x 1023
= 1.30 x 1014 kJ (Answer)