Question

if 8.6L of H2 reacted with 4.3L of O2 at STP, what is the volume of gaseous water collected (assuming none of it condenses)? 2H2(g) + O2(g) => 2H2O(g)

Answer 1

This may be a limiting reagent problem. You must determine which is the limiting reagent. To do this, I usually simply calculate how much of one reagent is needed if we start with the other. For example,
8.6 L H2 will require how much O2?
8.6 x (1 mol O2/2 mols H2) = 4.3 and we have exactly 4.3; therefore, both are limiting and we have exactly the amount of each we need. Use this same procedure to determine the amount of H2O produced.