Chem
posted by Valarie .
f 147 grams of FeS2 is allowed to react with 88 grams of O2 according to the following unbalanced equation, how many grams of Fe2O3 are produced?
FeS2 + O2 → Fe2O3 + SO2

This is a limiting reagent. You know that because BOTH of the reactant are given.
First, balance the equation.
Convert 147 g FeS2 to moles. moles = grams/molar mass.
Convert 88 g oxygen to moles.
Using the coefficients in the balanced equation, convert moles FeS2 to moles Fe2O3.
Same procedure, convert moles oxygen to moles Fe2O3.
It is more than likely that the two numbers for moles Fe2O3 will not agree which means one of them is wrong. In limiting reagent problems, the correct answer is ALWAYS the smaller value and the reactant providing that number is the limiting reagent.
Using the smaller value, convert to grams Fe2O3. g = moles x molar mass
Post your work if you get stuck. 
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