The balanced chemical equation that describes a particular reaction essentially tells you how many molecules of each reactant are needed in order for the reaction to take place.
More specifically, the coefficients that follow each chemical species that takes part in the reaction tells you how many molecules are involved in that reaction.
In your case, the balanced chemical equation that describes the synthesis of water looks like this
#color(red)(2)"H"_ (2(g)) + "O"_ (2(g)) -> 2"H"_ 2"O"_ ((l))#
This tells you that
Now, because molecules are so very, very small, we usually work with very large collections of molecules called moles.
A mole is simply a collection of
This means that the above reaction can be said to consume
You know that your container contains
In order to find the limiting reagent, you must determine which reactant will be completely consumed before every molecule of the other reactant gets the chance to take part in the reaction.
Since the reaction consumes twice as many moles of hydrogen gas than it does of oxygen gas, and since you have equal numbers of moles of each present in the mixture, you can say that hydrogen gas will be your limiting reagent.
More specifically, the reaction will consume all the moles of hydrogen gas and only
#8 color(red)(cancel(color(black)("moles H"_2))) * "1 mole O"_2/(color(red)(2)color(red)(cancel(color(black)("moles H"_2)))) = "4 moles O"_2#
Therefore, hydrogen gas,