Thermite Reaction

Question

Over the years, the thermite reaction has been used for welding railroad rails, in incendiary bombs, and to ignite solid fuel rocket motors. The reaction is

Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s)

 

What mass of iron(III) oxide must be used to produce 18.71 g of iron?

Answer 1

Replace 82.37 g Fe with 18.71 g Fe

Fe₂O₃(s) + 2Al(s) ==> 2Fe(l) + Al₂O₃(s)

Find moles of Fe and then from the stoichiometry, find moles of Fe₂O₃ needed. Finally, convert moles to g.

(1) moles Fe = 82.37 g Fe x 1 mol Fe/55.85 g = 1.4748 moles Fe

(2) moles Fe₂O₃ needed = 1.4748 mol Fe x 1 mol Fe₂O₃/2 mol Fe = 0.7374 moles Fe₂O₃ needed

(3) g Fe₂O₃ needed = 0.7374 mol Fe₂O₃ x 159.7 g/mol = 79.85 g Fe₂O₃ needed