# This is a Practice:Conservation of Mass-Energy. And I need help with 2 of them! Please Help!! ?

4.) The mass of a proton is 1.00728 atomic mass units (amu) and the mass of a neutron is 1.00867 amu. What is the mass defect (in amu) of a nucleus whose nuclear mass is 59.9338 amu? What is the mass defect in kilograms? What is the energy equivalent of this mass in kilojoules?

5.) The equation shows one mole of ethanol fuel being burned in oxygen. Convert the energy released into its equivalent mass. C2H5OH(l) + 3 O2(g) Æ 2 CO2(g) + 3 H2O (l) ΔH = -1418 kJ/mol

I'm Supposed to Use E=MC^2

### 1 Answer

- JimLv 72 months ago
Cobalt has an atomic number (Z) of 27, which means the nuclei of all its isotopes have 27 protons. Cobalt 60 has an atomic mass of 60, so it has 60-27 = 33 neutrons.

The mass of 27 isolated protons plus the mass of 33 isolated neutrons would be:

27*(1.007825 u) + 33*(1.008665 u) = 60.497220 u

The actual mass of the nucleus of 60-Co is 59.933820 u.

Mass defect: 60.497220 u - 59.933820 u = 0.563400 u

using the fact that 1 u = 931.5 MeV/c^2

(0.563400 u)*(931.5 MeV/u) = 524.807 MeV