The reaction of 2.5 mol of O2 with 4.6 mol of C3H8 will produce ________ mol of H2O.

Answer 1

This is a limiting reagent (LR) problem and we know that because amounts are given for BOTH reactants.

C3H8 + 5O2 ==> 3CO2 + 4H2O
mols H2O formed if we used 2.5 mol O2 and all of the propane we needed is 2.5 mol O2 x (4 mol H2O/5 mol O2) = 2.5 x 4/5 = 2 mol H2O formed.

mols H2O formed if we used 4.6 mol C3H8 and all of the O2 we needed That's 4.6 mol C3H8 x (4 mols H2O/1 mol C3H8) = 4.6 x 4/1 = 18.4

We have two answers for mols H2O formed and both of them can't be right. The correct answer in LR problems is ALWAYS the smaller value and the reagent providing that number is the LR. So 2 mols H2O will be formed.