Notes Unit 8 KEY

1 1 Unit 8 Stoichiometry Notes Stoichiometry is a big word for a process that chemist s use to calculate amounts in reactions. It makes use of the coefficient ratio set up by balanced reaction equations to make connections between the reactants and products in reactions. Stoichiometry calculates the quantities of reactants and products in a chemical reaction. The equation must be balanced! Questions that deal with amounts in reactions are examples of reaction stoichiometry. We already have the tools necessary to solve this question. We just need to learn a new way to apply skills such as writing chemical formulas, calculating formula masses, and converting from mass to moles , particles to moles , and volume of gases to moles .

2 Mole to Mole Conversions- you must have the Mole Ratio. Illustration: Let s use an analogy that we can understand to begin to understand the process. The KEY to any mole conversion is the ratio of coefficients in the reaction equation. Say I want to make a bacon double cheeseburger. Let s get our recipe together. 1 hamburger bun + 2 hamburger patties + 2 slices of cheese + 4 strips of bacon 1 bacon double cheeseburger Based on this recipe: 1) If I have five bacon double cheeseburgers: a. How many hamburger buns did you use? 5 hamburger bun b. How many hamburger patties did you use? 10 hamburger patties c.

3 How many slices of cheese did you use? 10 slices of cheese d. How many strips of bacon did you use? 20 strips of bacon 2) How many bacon double cheeseburgers can you make if you start with: a. 2 buns, 4 patties, 4 slices of cheese, 8 strips of bacon 2 bacon double cheese burgers b. 1 dozen buns, 2 dozen patties, 2 dozen slices of cheese, 4 dozen strips of bacon 1 dozen bacon double cheese burgers 2 c. 1 mole of buns, 2 mol of patties, 2 mol of cheese slices, 4 mol of bacon strips 1 mole of bacon double cheese burgers d. 10 buns, 20 patties, 2 slices of cheese, 40 strips of bacon 1 bacon double cheese burger To think through these questions we were using the ratios set up by the reaction equation ( recipe) We understood that to produce one complete bacon double cheeseburger we needed to have each of the above ingredients in a 1 bun to 2 patties to 2 slices of cheese to 4 slices of bacon.

4 This ratio is called the coefficient ratio. If we want to make 3 sandwiches then we would just triple all of the coefficients. THIS COEFFICIENT RATIO IS KEY TO DOING STOICHIOMETRY. Let s apply the above logic to a chemical recipe ( chemical reaction equation). 1 H2SO4 + 2 NaOH 1 Na2SO4 + 2 H2O If I use 1 mole of H2SO4 How many moles of sodium hydroxide do I need? 2 moles of NaOH How many moles of sodium sulfate do I make? 1 Mole of Na2SO4 Consider: Consider the reaction 2H2 + O2 2H2O. How many moles of water will be produced if there are moles of oxygen? pathway: mol of O2 mol of H2O moles O2 2 moles H2O = mol H2O 1 moles O2 Mole to mass .

5 How many grams of water will be produced if there are moles of oxygen? pathway: mol of O2 mol of H2O grams of H2O mol O2 2 mol H2O 18 g H2O = 130 g H2O 1 mol O2 1 mol H2O 3 mass to mass . What mass of barium phosphate can be produced from g of potassium phosphate reacting with barium nitrate? 2K3PO4 + 3Ba(NO3)2 Ba3(PO4)2 + 6 KNO3 pathway: grams of K3PO4 mol of K3PO4 mol of Ba3(PO4)2 grams of Ba3(PO4)2 g K3PO4 1 mol K3PO4 1 mol Ba3(PO4)2 g Ba3(PO4)2 = g Ba3(PO4)2 g K3PO4 2 mol K3PO4 1 mol Ba3(PO4)2 What mass of bromine gas can be produced from the complete reaction of potassium bromide and g of fluorine gas?

6 2 KBr + F2 Br2 + 2KF g F2 1 mol F2 1 mol Br2 g Br2 = 145 g Br2 38 g F2 1 mol F2 1 mol Br2 4 Mole to Mole Practice Consider the equation: aA bB moles of A b moles of B = moles of B a moles of A 1) N2 + 3 H2 2 NH3 How many moles of hydrogen are needed to completely react with two moles of nitrogen? 2 moles N2 3 moles H2 = 6 moles H2 1 moles N2 2) 2 KClO3 2 KCl + 3 O2 How many moles of oxygen are produced by the decomposition of six moles of potassium chlorate? 6 moles KClO3 3 moles O2 = 9 moles of O2 2 moles KClO3 3) Zn + 2 HCl ZnCl2 + H2 How many moles of hydrogen are produced from the reaction of three moles of zinc with an excess of HCl?

7 3 moles Zn 1 moles H2 = 3 moles of H2 1 moles Zn 4) C3H8 + 5O2 3CO2 + 4H2O How many moles of oxygen are necessary to react completely with four moles of propane (C3H8)? 4 moles C3H8 5 moles O2 = 20 moles of O2 1 moles C3H8 5) K3PO4 + Al(NO3)3 3 KNO3 + AlPO4 How many moles of potassium nitrate are produced when two moles of potassium phosphate react with two moles of aluminum nitrate? 2 moles K3PO4 3 moles KNO3 = 6 moles of KNO3 1 moles K3PO4 5 mass to Mole Practice Consider the equation: aA bB mass of A 1 mol A b mol B = moles of B Molar mass A a mol A Consider the following balanced equation to answer 1 3.

8 2 AgNO3(aq) + MgBr2(aq) 2 AgBr(s) + Mg(NO3)2(aq) 1) Calculate the mass of silver bromide produced from moles of silver nitrate. mol AgNO3 2 mol AgBr g AgBr =2 g AgBr 2 mol AgNO3 1 mol AgBr 2) Calculate the number of moles of magnesium nitrate formed from grams of silver nitrate. g AgNO3 1 mol AgNO3 1 mol Mg(NO3)2 = mol Mg(NO3) g AgNO3 2 mol AgNO3 3) Calculate the number of moles of silver bromide produced from 212 g of magnesium bromide. 212 g MgBr2 1 mol MgBr2 2 mol AgBr = mol AgBr g MgBr2 1 mol MgBr2 Consider the following balanced equation to answer 4 - 5. MnO2(s) + 4 HCl(aq) MnCl2 + 2 H2O(l) + Cl2(g) 4) Calculate the mass of MnO2 required to completely react with moles of water.

9 Mol H2O 1 mol MnO2 g MnO2 = 110 g MnO2 2 mol H2O 1 mol MnO2 5) What amount of chlorine gas is produced from 72 grams of HCl? 72 g HCl 1 mol HCl 1 mol Cl2 g Cl2 = 35 g Cl2 g HCl 4 mol HCl 1 mol Cl2 6 mass to mass Practice Consider the equation: aA bB Grams A 1 mol A b mol B Molar mass B = mass B Molar mass A a mol A 1 mol B 1) N2 + 3 H2 2 NH3 How many grams of hydrogen are necessary to completely react with g of nitrogen in the above reaction? 50 g N2 1 mol N2 3 mol H2 g H2 = g H2 g N2 1 mol N2 1 mol H2 2) 2 KClO3 2 KCl + 3 O2 a) How many grams of potassium chloride are produced if 25 grams of potassium chlorate decompose?

10 25 g KClO3 1 mol KClO3 2 mol KCl g KCl = 15 g KCl g KClO3 2 mol KClO3 1 mol KCl b) How many grams of oxygen are produced from 25 grams of potassium chlorate? 25 g KClO3 1 mol KClO3 3 mol O2 g O2 = g O2 g KClO3 2 mol KClO3 1 mol O2 3) Zn + 2 HCl ZnCl2 + H2 How many grams of hydrogen gas are produced from the reaction of 221 grams of zinc with an excess of HCl? 221 g Zn 1 mol Zn 1 mol H2 g H2 = g H2 g Zn 1 mol Zn 1 mol H2 4) Iron will react with oxygen to produce Fe2O3.