# LIMITING REACTANT LIMITING REACTANT Limiting Reagent The reactant

• Slides: 8

LIMITING REACTANT

LIMITING REACTANT • Limiting Reagent • The reactant that is totally used up during the chemical reaction • Limits the amount of product produced

EXCESS REACTANT • Excess Reagent • The reactant present in a quantity that is greater than what is needed to react with the limiting reactant • Remains after the limiting reactant has been used up

#1 Item Count #2 Projected # of S’mores Left over #3 Graham crackers 6 Marshmallows 2 Chocolate rectangle 3 3 2 1 0 0 0 1. Why don’t all of your projected # of S’mores in line #2 match the actual number of S’mores you can make? 2. What limited the total number of S’mores you can make? 3. What is another word for left over?

STEPS 1. Use stoichiometry to convert any reactants given into the specified product (if no product specified choose one) 2. Identify limiting reactant (LR), excess reactant (ER), and max amount of product 3. To calculate how much in excess, subtract the max amount of product and use stoichiometry to convert back to grams of reactant

EXAMPLE 1 How many grams of silver bromide can be formed when solutions containing 50. 0 g of magnesium bromide and 100. 0 g of silver nitrate are mixed together? What is the limiting reactant? What is in excess? 1 Mg. Br 2 + 2 Ag. NO 3 50. 0 g Mg. Br 2 1 mol Mg. Br 2 184. 11 g Mg. Br 2 100. 0 g Ag. NO 3 1 mol Ag. NO 3 169. 88 g Ag. NO 3 2 Ag. Br + 1 Mg(NO 3)2 2 mol Ag. Br 187. 77 g Ag. Br 1 mol Mg. Br 2 1 mol Ag. Br 2 mol Ag. Br 187. 77 g Ag. Br 2 mol Ag. NO 3 Limiting Reactant (LR) = Mg. Br 2 = 102 g Ag. Br = 110. 5 g Ag. Br 1 mol Ag. Br Excess Reactant (ER) = Ag. NO 3

EXAMPLE 2 How many grams of hydrogen chloride can be produced from 1. 00 g of hydrogen and 55. 0 g of chlorine? What is the limiting reactant? What is in excess? H 2 + Cl 2 2 HCl 1. 00 g H 2 55. 0 g Cl 2 1 mol H 2 2 mol HCl 36. 46 g HCl 2. 02 g H 2 1 mol HCl 1 mol Cl 2 2 mol HCl 36. 46 g HCl 70. 90 g Cl 2 1 mol HCl Limiting Reactant (LR) = H 2 = 36. 1 g HCl = 56. 6 g HCl Excess Reactant (ER) = Cl 2

EXAMPLE 3 How many grams of barium sulfate will be formed from 200. 0 g of barium nitrate and 150. 0 g of sodium sulfate? What is the limiting reactant? What is in excess? Ba(NO 3)2 + Na 2 SO 4 200. 0 g Ba(NO 3)2 1 mol Ba(NO 3)2 Ba. SO 4 + 2 Na. NO 3 1 mol Ba. SO 4 233. 40 g Ba. SO 4 261. 35 g Ba(NO 3)2 1 mol Ba. SO 4 = 178. 6 g Ba. SO 4 150. 0 g Na 2 SO 4 1 mol Na 2 SO 4 142. 05 g Na 2 SO 4 1 mol Ba. SO 4 1 mol Na 2 SO 4 233. 40 g Ba. SO 4 1 mol Ba. SO 4 = 246. 5 g Ba. SO 4 Limiting Reactant (LR) = Ba(NO 3)2 Excess Reactant (ER) = Na 2 SO 4