1. Stoichiometry Limiting Reactants

2. Stoichiometry Stoichiometry enables us to compare amounts of two substances in a balanced chemical reaction.

3. Simple Example If you have 6 slices of bread, how many ham sandwiches could you make? 2 Bread + 1 Ham → 1 Sandwich

4. Mole Ratios A mole ratio is a whole number relationship between two substances in a balanced chemical equation.

5. Converting Substances 2Na(s) + Cl 2 (g) → 2 NaCl(s) How many moles of salt could be made if you had 5.00 moles of chlorine gas? ANALYZE (have/need, conv. factor) PLAN (setup dimensional analysis) EVALUATE (crunch numbers) 5.00 mol Cl 2 1 mol Cl 2 2 mol NaCl 10 mol NaCl

6. Converting Mass to Mass 2H 2 (g) + O 2 (g) → 2H 2 O(l) How many grams of water could be made if you had 75.0 grams of oxygen? ANALYZE (have/need, conv. factors) PLAN (setup dimensional analysis) EVALUATE (crunch numbers) g O 2  mol O 2  mol H 2 O  g H 2 O 75.0 g O 2 32.00 1 mol O 2 1 2 mol H 2 O 1 mol H 2 O 18.02 g H 2 O 84.5

7. Limiting Reactants The first species that runs out in a reaction prevents the reaction from continuing. It is the limiting reactant. 1 body + 4 tires → 1 car

8. Excess Reactants The species that are left over from the beginning are excess reactants. 1 body + 4 tires → 1 car 8 bodies 1 body 4 tires 32 tires 48 tires – 32 tires = 16 excess tires

9. Percentage Yield We use percentage yield to determine how efficient a chemical reaction is. This can be done with grams or moles. Reactions cannot exceed 100% yield.

10. Percentage Yield Example If 152 grams of CO 2 are produced in a reaction, but the theoretical yield was calculated to be 175 grams of CO 2, what is the percentage yield?

11. Percentage Yield Practice Find the percentage yield if 5.50 moles of NaCl are produced from the reaction of 6.00 moles of sodium with excess chlorine gas. __Na + __Cl 2 → __NaCl

12. Percent Composition The percent composition of a substance indicates what percent of each atom is present in the compound (by mass). The sum of the percent compositions must be 100%

13. Percent Composition Example Find the percent composition of carbon in a sample of CO 2.