Step 1
The reaction must be completed and balanced as follows:
4 FeS2 + 11 O2 => 2 Fe2O3 + 8 SO2
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Step 2
Information provided:
26.62 moles of FeS2
59.44 moles of O2
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Step 3
The limiting and the excess reactant
Procedure: by stoichiometry,
4 FeS2 + 11 O2 => 2 Fe2O3 + 8 SO2
4 moles FeS2 ------------ 11 moles O2
26.62 moles FeS2 ------------ X
X = 26.62 moles FeS2 x 11 moles O2/4 moles FeS2
X = 73.20 moles
For 26.62 moles of FeS2, 73.20 moles of O2 are needed, but there are only 59.44 moles so the limiting reactant is O2, and the excess reactant is FeS2.
Answer:
The limiting reactant = O2
The excess reactant = FeS2