Identifying the Limiting Reactant Convert each reactant to grams of a product using stoichiometry The reactant that makes the least amount of products is the limiting reactant
Sample Problem Which is the limiting reactant if 25.0 grams of phosphorus reacts with 50.0 grams of oxygen? P 4 + 5O 2 P 4 O 10 P 4 is limiting
Sample Problem A 2.00 g sample of ammonia is mixed with 4.00 g of oxygen. How much NO is produced and which is the limiting reactant? 4 NH 3(g) + 5 O 2(g) 4 NO (g) + 6 H 2 O (g)
Sample Problem An alkaline battery produces energy according to the following reaction. Determine the limiting reactant if 25.0 g of Zn and 30.0 g of MnO 2 are used. What mass of Zn(OH) 2 is produced? Zn + 2MnO 2 + H 2 O Zn(OH) 2 + Mn 2 O 3 MnO 2 is limiting
Excess Reactants The amount of excess reactants can be determined by using stoichiometry to find the amount of reactants that is needed to react with the limiting reactant.
We're not finished yet though. 1.70 g is the amount of ammonia that reacted, not what is left over. To find the amount of excess reactant remaining, subtract the amount that reacted from the amount in the original sample.
Yield The theoretical yield represents the maximum amount of product that can be formed from given amounts of reactants The actual yield is the amount of product that actually forms when the reaction is carried out (in the laboratory). It is considered as an experimental value.
Percent Yield A ratio of actual yield to theoretical yield
Sample Problem Aluminum hydroxide is often present in antacids to neutralize stomach acid (HCl). If 14.0 g of aluminum hydroxide is present in an antacid tablet, determine the theoretical yield of aluminum chloride produced when the tablet reacts with stomach acid. If the actual yield of aluminum chloride is 22 g, what is the percent yield? Al(OH) 3 + 3HCl AlCl 3 + 3H 2 O