Question

How much energy is produced by a reaction of 33.5 g of iron with excess oxygen: 3Fe+2O2---->Fe3O4+1120kJ

Answer 1

Moles of iron in $33.5\ g=\frac{33.5}{55.84}=0.6$

$3Fe+2O_2\to Fe_3O_4+1120\ KJ$

$3$ moles of Iron produce $1120\ KJ$ of energy.

$0.6$ moles will produce $\frac{0.6}{3}\times 1120=224\ KJ$ of energy.