you start with 150.0g of pentane and 500.0L of O2. how many grams of H2O will you make?

Answer 1

This is a limiting reagent problem. I know that because amounts for BOTH reactants are given.
C5H12 + 8O2 ==> 5CO2 + 6H2O
mols C5H12 = grams/molar mass
mols O2 = L O2/22.4 = ?

Convert mols C5H12 to mols H2O using the coefficients in the balanced equation..
Convert mols O2 to mols H2O.
It is likely these two numbers will not be the same which means one of them is wrong. The correct value in limiting reagent problems is ALWAYS the smaller value and the reagent producing that value is the limiting regent.
Now convert the smaller value mols H2O to grams. g = mols x molar mass.