Presentation on theme: "Chapter 9 Reaction Stoichiometry"— Presentation transcript:
1 Chapter 9 Reaction Stoichiometry 9.1 Introduction to Stoichiometry
2 (STOY-KEE-AHM-EH-TREE) Stoichiometry(STOY-KEE-AHM-EH-TREE)The study of quantities of materials consumed and produced in chemical reactions.Composition Stoichiometry - deals with mass relationships of elements in compoundsReaction Stoichiometry - Involves mass relationships between reactants and products in a chemical reaction
4 Reaction Stoichiometry Problems Use Molar Mass!Use Mole Ratio!Use Molar Mass!GivenMolesUnknownMolesUnknownMassGivenMassGiven and unknown quantities are in molesGiven is an amount in moles and the unknown is a mass (usually in grams)Given is a mass in grams and the unknown is an amount in molesGiven is a mass in grams and the unknown is a mass in grams
5 given moles → unknown moles Mole RatioA conversion factor that relates the amounts in moles of any two substances involved in a chemical reactionThe coefficients in a balanced reaction will usually serve as a molar ratio!Mole ratio is used to convert:given moles → unknown moles
6 Molar Ratios C2H5OH + 3O2 → 2CO2 + 3H2O 1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of waterC2H5OH + 3O2 → 2CO H2OThe ratio of ethanol to oxygen is:1 mol to 3 molThe ratio of oxygen to carbon dioxide is:3 mol to 2 molThe ratio of carbon to hydrogen in ethanol is:2 mol to 6 mol, or 1 mol to 3 mol
12 Problem Solving Methods Ideal Stoichiometry - All reactants are converted into productsMass-Mass ProblemsStart with a known mass of reactant or product, find an unknown mass of another reactant or productAll other stoichiometry problems are derivations (shortened versions) of this larger solution
13 Problem Solving Methods Find Moles of Given using Molar MassUse Mole Ratios of find Moles of UnknownFind Grams of Unknown using Molar MassAssume all reactants turn into products!
14 Steps to Solving Problems Start with a correctly balanced chemical equation.Use key words in the problem statement to identify substances as either reactants or products.Determine what units you've been given and what you are being asked to find.Label each step with the correct units!The units from the numerator of the first step become the units in the denominator of the next step, and so forth.Stop when you have an answer with the units that you are searching for!
15 Solving a Stoichiometry Problem 6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed.Identify reactants and products and write the balanced equation.4Al+3O22Al2O3a. Every reaction needs a yield sign!b. What are the reactants?c. What are the products?d. What are the balanced coefficients?
16 Solving a Stoichiometry Problem 6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed?4 Al O2 2Al2O36.50 g Al1 mol Al2 mol Al2O3g Al2O3XXX=? g Al2O326.98 g Al4 mol Al1 mol Al2O36.50 x 2 x ÷ ÷ 4 =12.3 g Al2O3
18 Limiting Reactant The limiting reactant is the reactant that is consumed first, limiting the amounts of products formed.
19 Limiting Reactant? cookies. I find in my kitchen: 40 lbs. of butter I want to make chocolate chipcookies. I find in my kitchen:40 lbs. of buttertwo lbs. of salt1 gallon of vanilla extract80 lbs. of chocolate chips200 lbs. of flour150 lbs. of sugar150 lbs. of brown sugarten lbs. of baking sodaTWO eggsIt should be clear that the number of cookies I make will be limited by the number of eggs!
21 Identifying the Limiting Reactant Convert grams of each reactant to moles if the problem has not already done soUse molar ratios from the balance chemical equation to determine which reactant is limiting, and which reactant is in excessExcess ReactantThe substance that is not used up completely in a reaction
22 Stoichiometry with Limiting Reactants To calculate an amount of product produced:All calculations should start with the amount of the limiting reactant (LR), not the excess reactant (XS)!
23 Percent Yield Theoretical Yield The maximum amount of product that can be produced from a given amount of reactant (from stoichiometric calculations!)Actual YieldThe measured amount of a product obtained from a reaction (from laboratory experiments)
24 Calculating Percent Yield The ratio of the actual yield to the theoretical yield, multiplied by 100Percent Actual Yield XYield Theoretical Yield=