4Fe(s) + 3O2(g) → 2Fe2O3(s) ....... ΔH = -1.7 x 10^3 kJ
shows that 1700 kJ of heat is released when 4 moles of Fe react.
Molar mass of Fe = 56 g/mol
Molar mass of Fe2O3 = 160 g/mol.
(a) When 4 mol ( 4 x 56 = 224 g) iron reacted 1700 kJ are released,
when 9.0 g Fe reacted, the amount of energy will be
(9.0 x 1700) / (224) = 68.3 kJ
(b) According to the equation, 1700 kJ of energy released during the formation of 2 moles of Fe2O3 which is 2 x 160 = 320 g of rust.
120 kcal x (4.18 kJ / 1 kcal) = 501.6 kJ
When 1700 kJ released = 320 g rust
when 501.6 kJ released = (501.6 x 320) / 1700 = 94.4 g rust