How to find the limiting reactant given moles?
If you're given the moles present of each reactant, and asked to find the limiting reactant of a certain reaction, then the simplest way to find which is limiting is to divide each value by that substance's respective coefficient in the (balanced) chemical equation; whichever value is smallest is the limiting reactant.
As an example, let's say we have the reaction
and that we're given
#3#moles of hydrogen
#2#moles of oxygen
The limiting reactant is that whose value is smallest after dividing the mole number by their coefficient:
We see that the number for hydrogen is the lower value, so hydrogen is the limiting reagent.
Notice also how the limiting reactant isn't necessarily the reactant present in a larger quantity; there were
#3# #"mol H"_2#and #2# #"mol O"_2#, but hydrogen was limiting.