STOICHIOMETRY Chapter 9 Stoichiometry Mole-Mole Mass-Mole Mass-Mass Volume Chapter 9 Mixed mole

Stoichiometry Calculation of quantities in chemical equations From Greek words Stoichion = element Metron = measure

Two types of Stoichiometry The mole relationships of elements in compounds (empirical formulas) H3PO4 The mole relationships of reactants and products in a chemical equations (balanced equations) 2 H2 + O2  2H2O

Chemical Equations All balanced equations are always based on the units of the mole N2 + 3 H2  2 NH3 Translated: 1 mol N2 + 3 mol H2  2 mol NH3

Mole Ratio A conversion factor that relates the # of moles of any two substances involved in a chemical reaction Comes from a balanced equation

5 Types of Stoichiometry problems Mole-mole Mass-mass Volume-volume Particle-particle Mixed problems

1. mole-mole problems Moles of A  moles of B Mole ratio…

1. mole-mole problems – EX H2 + O2  H2O Balance it first! How many moles of hydrogen do you need to make 17 moles of water?

1. mole-mole problems – EX 2H2 + O2  2H2O Given: 17 moles water Unk: moles hydrogen? CF: Solve:

1. mole-mole problems – EX 2H2 + O2  2H2O How many moles of oxygen will you need to react with 334 moles of hydrogen? Blank Active Inspire for more practice

2. Mass – mass problems Mass A  Moles of A  moles of B  mass B Mole ratio…

mass-mass problems – EX Al + O2  Al2O3 Balance first!!! How many grams of aluminum do you need to make 15 grams of aluminum oxide?

mass-mass problems – EX 4Al + 3O2  2Al2O3 Given: 15 g Al2O3 Unk: ? g Al CF: 2 mol Al2O3 : 4 mol Al molar mass Al2O3 = 101.96 g/mol molar mass Al = 26.98 g/mol Blank Active Inspire for more practice

3. volume-volume problems Volume A  moles A  moles B  volume B

3. Volume-Volume Equations N2 + H2  NH3 How many liters of hydrogen do you need to make 25 liters of ammonia?

3. Volume-Volume Eqns N2 + 3H2  2NH3 Given: 25 L NH3 Unk: ? L H2 CF: 2 mol NH3 : 3 mol H2 STP conversion = 22.4 L / 1 mol Volume –p6

4. particle-particle problems Particles A  moles A  Moles B --. Particles B Mole ratio…

4. Particle-Particle Equations N2 + H2  NH3 How many molecules of hydrogen are needed to react with 3.784x1025 molecules of ammonia?

4. Particle-Particle Eqns N2 + 3H2  2NH3 Given: 3.784x1025 mo NH3 Unk: ? mo H2 CF: 2 mol NH3 : 3 mol H2 Avo’s Number = 6.02x1023/1 mol

5. Mixed mole problems ? unit A  moles A  Moles B  ? Unit B Mole ratio…

5. Mixed Eqns N2 + H2  NH3 What volume of ammonia at STP is produced if 25 g of nitrogen is reacted with excess hydrogen?

Mixed Eqns N2 + 3H2  2NH3 Given: 25 g N2 Unknown: ? L NH3 (mass-volume problem) CF: 1 mol N2 : 2 mol NH3 Mixed-p10

Limiting Reagents and Percent Yield Section 9.3

Bread is in excess which means there is some bread left over. 2 slices bread + 2 slices cheese = 1 grilled cheese sandwich How Many Sandwiches? If I have 12 slices bread? If I have 6 slices cheese? If I have 12 slices of bread and 6 slices of cheese? The amount of cheese limits how many sandwiches you can make. All of it’s used! Bread is in excess which means there is some bread left over.

Limiting Reagent Limiting Reagent = The reactant that limits the amount of products made Gets completely used up in a reaction Excess reagent = the reactant that is not used up completely There is more than enough leftover

Steps to determine LR & ER Set up two mass-mass problems. Compare the amounts of product. Identify Limiting reagent = reactant that makes the least amount of product. Determine how much ER is used based on the amount of LR given in a third mass-mass problem. Subtract the amount of ER used from the given amount to determine how much ER is leftover.

EX: Limiting & Excess Reagents C + O2  CO2 Complete two mass-mass problems with information given to determine limiting reagent 55 g 35 g

EX: Limiting & Excess Reagents C + O2  CO2 Limiting Reagent = How much ER will you use? How much ER leftover? 55 g 35 g Page 11

Percent Yield Used to determine how accurate a person is in the lab Percent yield = actual yield X 100 theoretical yield Actual yield = the amount of product produced in the lab Theoretical yield = the amount of product that should have been produced in theory

EX; Percent Yield What is the percent yield if John made 15.87 g of chalk and he calculated that he should have made 22.5 grams of chalk? Actual yield = Theoretical yield = Percent yield =

END OF CHAPTER QUESTIONS Page 262 # 36, 37, 38, 41, 42, 44, 45, 46