Answer to Question #198786 in General Chemistry for Jerry

Question

For Al-28, calculate a) the mass defect (use Table 18.4) and b) the binding energy in 

kJ/mol.

Answer 1

Solution

Al-28 =27.981910 amu

Al has 13 protons

28-13=15

15 neutrons

proton=1.00727647 amu

Neutron=1.00866490 amu

predicted mass =13(1.00727647)+15(1.00866490)

=28.22456761 amu

Mass defect= Predicted mass - Actual mass

28.22457-27.98191= 0.24266 amu

b) Binding energy

E=mc²

1 amu = 1.66054 x 10^-27kg

c= 2.99792 x10⁸

(0.24266 x 1.66054 x 10^-27) x (2.99792 x 10⁸)

= 3.62149 x10^-11 J

convert to KJ/mole

$\frac{3.62149 \times 10^-11}{6.022 \times 10^20}$

=6.01377 x 10^-32KJ/mol