2 TOPICS Everyday Stoichiometry Simple Stoichiometry Calculating Amount of Product or ReactantLimiting ReagentPercent Yield
3 Standards Addressed: Conservation of Matter and Stoichiometry 3a. Students know how to describe chemical reactions by writing balanced chemical equations3d. Students know how to determine the molar mass of a molecule from its chemical formula and a table of atomic masses an how to convert the mass of a molecular substance to moles, number of particles, or volume of gas at STP.3e. Students know how to calculate the masses of reactants and products in a chemical reaction from the mass of one of the reactants or products and the relevant atomic masses.
4 DefinitionsStoichiometry: the study of mass relationships on chemical equations.Excess: more than enough available; won’t run out of that reactantMole-mole ratio: how two substances are numerically related to each other in units of moles; you get these numbers from the balanced chemical equation.
5 Everyday Stoichiometry: 2 wheels + 1 frame → 1 bikeHow many wheels and frames do you need to make 5 bikes?If you have 6 wheels and 4 frames, how many bikes can you make?If you have 11 wheels and 3 frames, how many bikes can you make?
6 TOPICS Everyday Stoichiometry Simple Stoichiometry Calculating Amount of Product or ReactantLimiting ReagentPercent Yield
7 Simple Stoichiometry: Here is the “recipe” for water:2 H2 + O2 → 2 H2O*This recipe says:2 molecules of H2 react with 1 molecule of O2 to produce 2 molecules of water2 moles of H2 react with 1 mole of O2 to produce 2 moles of water
8 Question How many hydrogens and oxygens do you need to make 8 waters? How many waters can you make from:10 H2 and 4 O25 H2 and 3 O225 H2 and 16 O2Which of each is in excess?
9 Question Here is the “recipe” for diphosphorus pentoxide: 4 P + 5 O2 →2 P2O5How many phosphorus and oxygens do you need to make 4 diphosphorus pentoxide?How many diphosphorus pentoxide can you make from:12 P and 20 O221 P and 21 O2
10 TOPICS Everyday Stoichiometry Simple Stoichiometry Calculating Amount of Product or ReactantLimiting ReagentPercent Yield
11 Mole-Mole Ratios Come from the balanced chemical equation Ratio made between the “given” substance and the “get” substanceUse the coefficients of the “given” and “get” from the balanced chemical equationRatios can be between any 2 substancesReactant-reactantReactant-productProduct-product
12 Mole-Mole Ratio Examples 2 H2 + O2 → 2 H2O2 mole H2 2 mole H2O1 mole O mole H2
13 Mole-Mole Ratio Examples Fe2O3 (s) + 3 CO (g)→ 2 Fe (s) + 3 CO2 (g)Write a mol-mol ratio between the reactants…Write a mol-mol ratio between a product and a reactant…Write a mol-mol ratio between a product and a product
14 Calculating Amount of Reactant Needed 2 P + 3Cl2 → 2 PCl3How many moles of phosphorus are consumed if 12 moles of phosphorus trichloride are produced?
15 How Much Product is Produced? 2 P + 3Cl2 → 2 PCl3How many moles of PCl3 can be formed from 5 moles chlorine and excess phosphorus?
16 Question2 H2 + O2 → 2 H2OHow many moles of water are produced by burning 2.72 mol H2 in an excess of O2?
17 Question2 H2 + O2 → 2 H2OWhat mass of O2 is consumed in the complete combustion of 6.86g H2 ?
18 Question 2 Ag2CO3 (s) → 4 Ag(s) + 2CO2(g) + O2(g) How many grams of Ag2CO3 must have decomposed if 75.1 grams of Ag were obtained in the reaction?
19 Question 2 Ag2CO3 (s) → 4 Ag(s) + 2CO2(g) + O2(g) How many grams of carbon dioxide were produced if 25.0 g of oxygen were produced?
20 Let’s Summarize the Steps Is there a balanced chemical equation?Write down the “given” and the “get”Mini road map…g-mol-mol-gSet-up a dimensional analysis equationCancel units and calculateReport answer to correct # of sig. figs.
21 THE LONGEST “MINI ROAD MAP” YOU WILL HAVE TO FOLLOW GRAMS-MOLES-MOLES-GRAMS
22 Question KClO3 + 5 KCl + 6 HNO3 → 6KNO3 + 3Cl2 + 3 H2O How many grams of KClO3 are required to prepare 10.0g of Cl2 ?
23 Iron (II) oxide decomposes into iron and oxygen gas. 2 FeO → 2 Fe + O2How many grams of FeO are needed to produce 140g of Fe?
24 Hydrochloric acid reacts with zinc metal to produce zinc chloride and hydrogen gas 2 HCl + 2 Zn → ZnCl2 + H2How many grams of hydrochloric acid are required to react completely with 1.00g of zinc?
25 Topics Everyday Stoichiometry Simple Stoichiometry Calculating Amount of Product or ReactantLimiting ReagentPercent Yield
26 Anticipatory Set3 cups flour + 2 cups sugar + 1 cup butter + 3 eggs = 1 batchFlour Sugar Butter Eggs13 cups cups cupsHow many batches of cookies can we make? How did you figure it out?Flour-4 Sugar-5 Butter-3 Eggs-7, so we can only make 3 batches. The butter yields the smallest amount possible that can be produced. The butter tells how many bathes we can make; therefore the butter is the limiting ingredient.
27 SummarizeHere, we did multiple calculations side by side and then chose the correct result.We can use this same type of reasoning/procedure to calculate the limiting reagent in a given chemical reaction.
28 DefinitionLimiting reagent: the reactant that is completely used up in the chemical reaction. The limiting reagent determines how much product can be formed.Calculating Limiting ReactantWhich reactant will run out first? You can’t tell just by looking at it, so you need to do some calculations.NOTE: In limiting reagent problems, BOTH REACTANTS are converted to the same PRODUCT
29 Calculating the Limiting Reagent P4 + 6 Cl2 → 4 PCl3What mass of PCl3 forms in the rxn of 125g P4 with 323 g Cl2?
30 Limiting Reagent CH4 + 2 O2 → CO2 + 2 H2O If 12.0g CH4 and 30.0g O2 react to form CO2 and H2O, how many grams of CO2 will be formed?
31 Summarize the Steps we followed 1. Is there a balanced chemical equation?2. Write down the 2 “givens” (both reactants) and the “get” (the product)3. Set-up Dimensional Analysis equations; 1 for each giveng-mol-mol-g4. Whichever reactant produced the smaller amount of product, that reactant is the limiting reagent5. Make your concluding statement
32 Topics Everyday Stoichiometry Simple Stoichiometry Calculating Amount of Product or ReactantLimiting ReagentPercent Yield
33 DefinitionsTheoretical Yield: How much product you expect to get based on your calculationActual Yield: Amount of product actually produced when the reaction is conducted… this amount is always stated in the problemPercent Yield: the percentage of theoretical yield obtained from the reaction
34 Calculating Percent Yield % Yield = actual yield X 100%theoretical yield
35 Calculating Percent Yield Determine the percent yield for the reaction between 98.7g of Sb2S3 and excess oxygen if 72.4 g of Sb4O6 are recovered along with an unknown amount of sulfur dioxide gas.