Question: how many moles of water are produced when 4.5 mol of o2 fully react?
Answer: As you know, the stoichiometric coefficients attributed to each compound in the balanced chemical equation can be thought of as moles of reactants needed or moles of products formed in the reaction. Notice that the reaction requires 2 moles of hydrogen gas and 1 mole of oxygen gas to produce 2 moles of water.