2StoichiometryThe quantitative study of reactants and products in a chemical reactionChemical reactions give info about how molecules combine, and can be used to determine amounts of substances that form
3Mole to Mole Calculations When using a chemical equation to determine the amount of the substance, you must relate them by their mole ratiosExample #1:____ H2 + ____ O2 → ____ H2OIf you start with 4 moles of O2 how many moles of H2O would form?
4Mole to Mole Calculations Example #2:___ Fe + ____ S → ___Fe2S3How many moles of iron (III) sulfide, Fe2S3, forms if the reaction initially starts with 8 moles of iron, Fe?
5Mass to Mass Calculations Example #1:___ H2 + ___ O2 → ___ H2OIf 2.4 g of O2 are reacted with excess H2 gas, how many moles of H2O would form?0.15 mol H2O
6Mass to Mass Calculations Example #2:___ H2 + ___ O2 → ___ H2OIn the above equation, if I started with 3 grams of H2, how many grams of H2O would form?26.8 g H2O
7Mass to Mass Calculations Example #3:_ NH3 (g) + _ CO2 (g) → _ (NH2)2CO(aq) + _H2O(l)When 2.00 grams of ammonia, NH3, react with excess CO2, what mass of water (in grams) is formed?1.06 g H2O
8Limiting Reactant The reactant used up first in a chemical reaction Also called limiting reagentAfter a reaction, excess reactants are leftThese are reactants present in greater quantities that remain after a reaction takes place
94 legs + 1 seat + 10 screws → 1 chair Limiting ReactantChair analogy:It’s your lucky day! Mr. Nelson has hired you to make chairs! The chairs follow the “reaction”:4 legs + 1 seat + 10 screws → 1 chairHere are the supplies you have: 10 legs, 5 seats, and 100 screws. How many chairs be made? What is the limiting reactant?
11Limiting ReactantThe limiting reactant can be found by determining which of the starting amounts yields the least amount of product
12Limiting Reactant Example Problem Sodium chloride can be prepared by the reaction of sodium with chlorine gas:2Na (s) + Cl2 (g) ® 2NaCl (s)Suppose that 6.70 mol Na reacts with 3.2 mol Cl2How many moles of NaCl will be formed in this reaction?What is the limiting reactant? Cl26.4 mol NaCl
13Limiting Reactant Practice Problem 2.70 mol C2H4 is reacted with 6.30 mol of O2. Calculate the amount in moles of water that forms, and identify the limiting reactant.C2H4 (g) + 3O2 (g) ® 2CO2 (g) + 2H2O (g)4.2 mol H2O
14Limiting Reactant Example Problem Urea is prepared by reacting ammonia with carbon dioxide:2 NH3 (g) + CO2 (g) → (NH2)2CO(aq) + H2O(l)In one process, g of NH3 are treated with 1142 g of CO2. Calculate the mass of urea, (NH2)2CO, formed.1122 g urea
15Limiting Reactant Practice Problem Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with 8.25 g of nitrogen. The balanced equation is:N2 + 3 H2 ® 2 NH39.97 g NH3
16Percent YieldTheoretical yield is the amount of product that would result if all the limiting reagent reactedActual yield is the amount actually obtained in lab from a reactionActual yield is almost always less than theoretical
17Percent YieldPercent yield describes proportion of actual yield to theoretical yield.
18Percent Yield Example Problem When 84.8 g of iron (III) oxide reacts with an excess of carbon monoxide, 54.3 g of iron is produced. What is the percent yield of this reaction?Fe2O3 (s) + 3CO (g) ® 2 Fe (s) + 3CO2 (g)91.6%
19Percent Yield Practice Problem If 25 grams of carbon dioxide gas can be produced in the following reaction, how many grams of sodium hydroxide should be produced? If 10.7 grams of sodium hydroxide are actually produced, what is the percent yield?NaHCO3 ® NaOH + CO222.7 g NaOH / 41.1%