# Limiting Reactant Percent Yield Ms. M. Mack May 13-14, 2009.

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Limiting Reactant Percent Yield Ms. M. Mack May 13-14, 2009

Bell Ringer Determine the percent composition of phosphoric acid.

Stoichiometry Overview Stoichiometry is the study of the quantitative relationships between amount of reactants used and products formed in a chemical reaction. It is based on the law of conservation of mass. In a chemical reaction, the mass of the reactants must equal the mass of the products.

Try this on for size… An automotive shop has 8 car bodies. There are 50 tires available. How many cars can the automotive shop manufacture? How many tires (if any) will remain?

What determines how much product will be formed in a reaction?

Let’s find out! Turn in your textbook to pg. 364 in your textbook. We will read the subheading: “Why do reactions stop?” When you discover the answer to the question on the previous slide, raise your hand!

Limiting Reactant The limiting reactant in a chemical reaction is the reactant that limits the amount of product formed. The reaction will stop when the limiting reactant is completely consumed.

How do we identify the limiting reactant?

Steps 1. Balance the equation and identify the mass of each reactant present. 2. Use stoichiometric calculations to find out how much product is formed by each reactant. (choose one product for comparison) 3. The reactant that produces the lesser amount of product is the limiting reactant!

Practice NaOH (aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + H 2 O (g) In the reaction above, 40.0 g of sodium hydroxide reacts with 60.0 g of sulfuric acid. Balance the equation. Choose one product for comparison. Identify the limiting reactant!

Why use excess reactants? In nature, chemical reactions rarely occur in the exact amounts specified by the balanced equation. One reactant is limiting and the other is excess. Let’s read pgs. 368-369 to find out why it is important to use excess reactant. When you discover the answer, please raise your hand!

Please complete: Pg. 369 # 22-24 Pg. 368 # 20 in the yellow box (a, b only)

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