Warm-up 5.11 S’MORES FACTORY One afternoon you return home and decide to make s’mores for yourself and friends. To make 1 s’more you need 4 graham crackers, 1 marshmallow, & 2 chocolate squares. In the pantry you find 20 whole graham cracker (4 squares each), an entire bag of marshmallows (100+) and 3 chocolate bars (8 pieces each). How many s’mores can you make? Why can’t you make more? Which part limited how many you could make?   Relationships

Limiting Reactant LIMITING REACTANTS A. The reactant that produces the least amount of product is the- Limiting Reactant B. The reactant that is not completely used up is in- Excess C. Determining the limiting reactant: Step 1- Write the Balanced equation Step 2- Calculate the mass of one of the products using the masses given for each reactant (2 problems) Step 3- Determine which produces the smaller amount of product= Limiting Reactant

Example 1 Some rocket engines use a mixture of hydrazine, N2H4 and hydrogen peroxide H202 as the propellant. The products are nitrogen gas and water vapor. What is the limiting reactant if 0.750 moles of hydrazine is mixed with 0.500 moles of hydrogen peroxide? Step 1- Write the balance equation  

Step 2- Calculate mass of one of the products (pick the simplest) 2 problems Which is the limiting reactant? ______________________ Which is in excess?_______________________________ How much product will be produced?___________________

Example 2 Aspirin (C9H8O4) is synthesized by the reaction of salicylic acid (C7H6O3) with acetic anhydride (C4H6O3). Water is the other product. When 20.0 grams of salicylic acid and 20.0 grams of the anhydride react which is the limiting reactant?

Which is the limiting reactant? ______________________ Which is in excess?_______________________________ How much product will be produced?___________________

Percent Yield Rarely in a chemical reaction will you get 100% of your product(s). Things often “go wrong” or get messed up. Even without errors product often “get lost” in equipment or evaporates before it can be collected.   Theoretical Yield - When Stoichiometry is used to calculate the amount of products that should be formed from the reactants. Actual Yield- The amount of product that is actually formed in the lab. Usually less

Percent Yield- what percentage of the actual amount obtained compared to the theoretical amount   Actual Yield x 100 = % Yeild Theoretical Yield ***Memorize this formula!!!!!!!!!!!

Example: A piece of Copper with a mass of 5 Example: A piece of Copper with a mass of 5.00 g is placed in a AgNO3 solution in excess. The silver metal produced has a mass of 15.2 g. What is the percent yield?   Step 1- Write Balance Equation Step 2- Calculate the Theoretical Yield Step 3- Calculate % Yield