Stoichiometry Notes Chemistry Mrs. Stoops

Stoichiometry Notes Converts grams of one substance into a different substance. Uses: Balanced chemical equations Mole ratio Mole conversions (grams  moles)

Recipe Connection Chocolate chip cookies – makes 60 cookies 2 1/4 cups all-purpose flour 1 teaspoon baking soda 1 teaspoon salt 1 cup (2 sticks) butter, softened 3/4 cup granulated sugar 3/4 cup packed brown sugar 1 teaspoon vanilla extract 2 large eggs 2 cups (12-oz. pkg.) NESTLÉ® TOLL HOUSE® Semi- Sweet Chocolate MorselsNESTLÉ® TOLL HOUSE® Semi- Sweet Chocolate Morsels

Mole ratio EX: SiO C  SiC + 2 CO 14 g C? g CO The coefficients represent the ratios of all the reactants and products to each other 1 mole SiO 2 = 3 mole C = 1 mole SiC = 2 mole CO SO we can take the parts we want out to solve our problem. MOLE RATIO 3 mole C = 2 mole CO

The process EX: SiO C  SiC + 2 CO 14 g C? g CO You can change the mole C into mole of CO using mole ratio, then... If you can change the 14 g C into mole C using the molar mass, then... You can change the mole CO into gram CO using molar mass!

Solve the problem EX: SiO C  SiC + 2 CO 14 g C ? g CO The set-up:

Example #2 EX:2 C 2 H O 2  4 CO 2 + 2H 2 O 23 g CO 2 ? gH 2 O

Part 2 A + B  C 10 g A ? g C 10 g A x 1 mol A x 1 mol C x ~ g C = g C ~ g A 1 mol A 1 mol C gA mol A mol C g C molar mole molar mass ratio mass The basic set-up ROAD MAP

Other versions #1 EX: 2H 2 + O 2  2H 2 O 2.1 mol O 2 ? gH 2 O The set-up:Moles A to grams C2 fractions Mole Ratio Molar Mass

Other versions #2 EX: 2H 2 + O 2  2H 2 O 3.1 mol H 2 O ? mol H 2 The set-up:Moles A to moles C1 fraction Mole Ratio

You have the following materials: 19 slices of bread 10 slices of cheese 12 slices of lunch meat 10 slices of tomato Each sandwich needs: 2 slices of bread 1 slices of cheese 1 slices of lunch meat 1 slices of tomato What runs out first? How many sandwiches do you make?

Limiting Reactant Pt3 Limiting Reactant – “Which runs out first?” EX: Ca(OH) 2 + 2HCl  CaCl 2 + 2H 2 O If you have 6.3 mol HCl and 2.8 mol Ca(OH) 2 which will be completely used up? 2 reactants; pick one! Start with one number given in the problem And change it to the other number given Moles to moles1 fraction

Continued OR NEEDED Which limits? HAVE Ca(OH) 2 Limits

Limiting example EX:2 KBr + Cl 2  2KCl + Br g KBr g Cl 2 OR Limiting Reactant = Cl g Cl g KBr Which limits?

A little twist... The question may ask you how much you actually produce. First you find the limiting reactant, then... Take the limiting reactant and do stoichiometry on it to find the product they ask for.

If you follow the recipe from the sandwiches and you have enough ingredients to make 15 sandwiches. BUT, the tomato is bad in spots, so only make 11 sandwiches. What is your percent yield? 73 % Percent Yield Pt 4

Percent Yield = How much we made compared to how much we could have made. In real words... Will NEVER be more than 100% If you were perfect! Always start with the reactant

EX: C 6 H 6 + Cl 2  C 6 H 5 Cl + HCl When 36.8 g C 6 H 6 reacts, the actual yield is 38.8 g C 6 H 5 Cl. What is the percent yield? 52.8 g C 6 H 5 Cl 73.4 %