The balanced chemical equation for the reaction of iron with steam is:
3Fe+4H2O→Fe3O4+4H2
Molar mass of H2O=2×1+16=18 g mol−1
Number of moles of steam (H2O) given = 1818=1 mol
From the balanced equation, 4 moles of H2O react with 3 moles of Fe.
Therefore, 1 mole of H2O will react with 43 moles of Fe.
Mass of iron reacted = Moles of Fe× Molar mass of Fe
Mass of iron = 43×56=3×14=42 g
Answer: 42 g