1. Limiting Reagents Stochiometry Chapter 9 Chemical Reactions

2. Limiting Reactants Let imagine making a cheese sandwich. For each sandwich you will need 5 slices of cheese and two slices of bread. What would the chemical reaction for this recipe look like:

3. C 5 + B 2 C 5 B 2 Based on this recipe, how many sandwiches can we make if we have 11 pieces of bread and more cheese than we could ever possibly use (excess ham)?

4. Limiting and Excess A limited reactant is the reactant that limits the amount of the other reactants that can combine and the amount of product that can form in a chemical reaction. An excess reactant is the substance that is not used up completely in a reaction

5. Determine the Limiting Reactant 1. Determine the amount of product that can be produced from each reactant: the reactant that gives less product is limiting. –EX. Find the number of “sandwiches” you can make from each “ingredient” 2. For the given amount of each reactant, find the amount of the other reactant needed; if the amount of reactant actually present is less than the amount needed, that reactant is limiting –EX. Find out how much of each “ingredient” you need to completely use up the other, and check if you have this amount

6. Practice: SiO 2 + 4 HF  SiF 4 + 2 H 2 O If 2.0 mol of HF are exposed to 4.5 mol SiO 2, which is the limiting reactant? 2 mol HF X 1mol SiO 2 /4 mol HF =.50 mol SiO 2 Because.50 mol SiO 2 is less than what is given this is the excess making HF the limited.

7. Limiting Reagent Problems 2 Al + 3 I 2  2 AlI 3 Determine the limiting reagent and the theoretical yield of the product if one starts with 1.20 mol Al and 2.40 mol iodine. Determine the amount if 1.20 g Al and 2.40 g iodine is reacted? How many grams Al are left over?

8. Typical Problem 15 g aluminum sulfide and 10.00 g water react until the limiting reagent is used up. Here is the balanced equation for the reaction: Al 2 S 3 + 6 H 2 O  2 Al(OH) 3 + 3 H 2 S 1.Which is the limiting reagent? 2.What is the maximum mass of H 2 S which can be formed from these reagents? 3.How much excess reagent remain after the reaction is complete?