If I need 2.2 moles of CO2, and I have excess Fe2O3, how many moles of C do I need?

2Fe2O3 + C - -> Fe + 3CO2

0.733 mol.

Explanation:

From the balanced equation:

2Fe₂O₃ + C → Fe + 3CO₂,

It is clear that 1.0 moles of Fe₂O₃ react with 1.0 mole of C to produce 1.0 mole of Fe and 3.0 moles of CO₂.

Since Fe₂O₃ is in excess, C will be the limiting reactant.

Using cross multiplication:

1.0 mole of C produces → 3.0 moles of CO₂, from the stichiometry.

? mole of C produces → 2.2 moles of CO₂.

∴ The no. of moles of C needed to produce 2.2 moles of CO₂ = (1.0 mole of C) (2.2 mole of CO₂) / (3.0 mole of CO₂) = 0.733 mol.