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There are two types of Stoichiometry. The composition part "deals with the mass relationships of elements in compounds" as stated in our chemistry text book. Another quote from the same books states that reactions stoichiometry "involves the mass relationships between reactants and products in a chemical reaction. The trick to comparing amounts of two or more substances in moles is looking at the coefficients. In the equation: 2AlO(l)-->4Al(s)+ 3o(g), you say that the relationship between Aluminum oxide and Oxygen gas is 2:3, meaning that if i have 6 moles of Aluminum oxide, I will have 9 moles of Oxygen gas. The limiting reaction in an equation is the molecule or element that will be gone in the reaction, therefore ceasing it. The way to determine the limiting reactant (only on the left side of the arrow) is to compare the specific two reactants with eachother. First, turn the gram amounts given for each molecule into moles. Then compare the discovered ratio with the given ratio in the equation. For instance, if I had 10 grams each of HCl and HO, and their coeffiecents are 2 and 3, respectively, than the limiting reactant would be hydrochloric acid. When you determine the amount of products produced, always use ratios with the limiting reactant. That way, you will know exactly the maximum amount of product possible. :)