7/6/20161 Chap 9: Stoichiometry

7/6/20162 Section 9-1 Introduction to Stoichiometry Define stoichiometry. Describe the importance of the mole ratio in stoichiometric calculations. Write a mole ratio relating two substances in a chemical reaction.

7/6/20163 The Arithmetic of Eq’ns: Tricycle making: –F–F–F–F + S + 3W + H + 2 P  FSW3HP2 Ex: How many tricycle seats, wheels, and pedals are needed to make 288 tricycles? –2–2–2–288 S; 3x288 W; 2x288 P

In terms of Moles The coefficients tell us how many moles of each kind. Mole ratio - conversion ratio that relates the amounts in moles of any two substances in a chemical reaction. Molar mass - mass, in grams, of one mole of a substance.

7/6/20165 Writing Mole Ratios 4 Fe + 3 O 2 2 Fe 2 O 3 Fe and O 2 4 mole Fe and 3 mole O 2 3 mole O 2 4 mole Fe Fe and Fe 2 O 3 4 mole Feand2 mole Fe 2 O 3 2 mole Fe 2 O 3 4 mole Fe O 2 and Fe 2 O 3 3 mole O 2 and 2 mole Fe 2 O 3 2 mole Fe 2 O 3 3 mole O 2

7/6/20166 Identify a mole ratio 3 H 2 (g) + N 2 (g) 2 NH 3 (g) A. A mole ratio for H 2 and N 2 is? 1) 3 mole N 2 2) 1 mole N 2 3) 1 mole N 2 1 mole H 2 3 mole H 2 2 mole H 2 This one! B. A mole ratio for NH 3 and H 2 is? 1) 1 mole H 2 2) 2 mole NH 3 3) 3 mole N 2 2 mole NH 3 3 mole H 2 2 mole NH 3 This one! This one!

In terms of mass The law of conservation of mass applies We can check using moles 2H 2 + O 2   2H 2 O 2 moles H g H 2 1 moles H 2 =4.04 g H 2 1 moles O g O 2 1 moles O 2 =32.00 g O g H 2 + O 2

In terms of mass 2H 2 + O 2   2H 2 O 2 moles H 2 O g H 2 O 1 mole H 2 O = g H 2 O 2H 2 + O 2   2H 2 O g (H 2 + O 2 ) =36.04 g H 2 O

Your turn Show that the following equation follows the Law of conservation of mass. 2 Al 2 O 3 Al + 3O 2... You should have what number of grams on both sides? g

7/6/ Ideal Stoichiometric Calculations Calculate the amount in moles of a reactant or product from the amount in moles of a different reactant or product (moles “A” to moles “B”) Calculate the mass of a reactant or product from the amount in moles of a different reactant or product (moles “A” to mass “B”). Calculate mass “A” to moles “B”. Calculate mass “A” to mass “B”.

7/6/ Chemical Calculations: Mole to Mole 4 Fe + 3 O 2 2 Fe 2 O 3 How many moles of Fe 2 O 3 are produced when 6.0 react? (What is mole ratio?...) How many moles of Fe 2 O 3 are produced when 6.0 moles O 2 react? (What is mole ratio?...) 6.0 mol O 2 x 2 mol Fe 2 O 3 = 4.0 mol Fe 2 O 3 3 mol O 2

Mole to mole conversions 2 Al 2 O 3 Al + 3O 2 every time we use 2 moles of Al 2 O 3 we make 3 moles of O 2 2 moles Al 2 O 3 3 mole O 2 or 2 moles Al 2 O 3 3 mole O 2

Mole to Mole conversions How many moles of O 2 are produced when 3.34 moles of Al 2 O 3 decompose? 2 Al 2 O 3 Al + 3O moles Al 2 O 3 2 moles Al 2 O 3 3 mole O 2 = 5.01 moles O 2

Your Turn 2C 2 H 2 + 5O 2  4CO 2 + 2H 2 O If 3.84 moles of C 2 H 2 are burned, how many moles of O 2 are needed? Ans x 5/2 = 9.6 moles O 2 How many moles of C 2 H 2 are needed to produce 8.95 mole of H 2 O? x 2/2 = 8.95 moles C 2 H 2 If 2.47 moles of C 2 H 2 are burned, how many moles of CO 2 are formed? x 4/2 = 4.94 moles CO 2

How do you get good at this?

7/6/ Learning Check 2 4 Fe + 3 O 2 2 Fe 2 O 3 4 Fe + 3 O 2 2 Fe 2 O 3 How many moles of Fe are needed to react with 12.0 mol of O 2 ? 1) 3.00 mol Fe 2) 9.00 mol Fe 3) 16.0 mol Fe (Solution next slide)

7/6/ Solution S2 4 Fe + 3 O 2 2 Fe 2 O mol O 2 x mol Fe = 16.0 mol Fe mol O 2 mol O 2 4 3

7/6/ Mass in Chemical Reactions How much do you make? How much do you need? 18

7/6/ Calculating Mass of A Substance n Balance the equation first! n Convert starting amount to moles n Use coefficients to write a mole ratio n Convert moles of desired to grams n Mole Island does this for you.

7/6/ Calculation The reaction between H 2 and O 2 produces 13.1 g of water. How many grams of O 2 reacted? The reaction between H 2 and O 2 produces 13.1 g of water. How many grams of O 2 reacted? Write the equation H 2 (g) + O 2 (g) H 2 O (g) Balance the equation 2 H 2 (g) + O 2 (g)2 H 2 O (g) 2 H 2 (g) + O 2 (g)2 H 2 O (g)

7/6/ Organize data mol bridge mol bridge 2 H 2 (g) + O 2 (g)2 H 2 O (g) 2 H 2 (g) + O 2 (g)2 H 2 O (g) ? g 13.1 g ? g 13.1 g Plan g H 2 O mol H 2 O mol O 2 g O 2 Setup 13.1 g H 2 O x 1 mol H 2 O x 1 mol O 2 x 32.0 g O g H 2 O2 mol H 2 O 1 mol O 2 = 11.6 g O 2 = 11.6 g O 2 BA

7/6/ For example... If 10.1 g of Fe are added to a solution of Copper (II) Sulfate, how much solid copper would form?... Fe + CuSO 4  Fe 2 (SO 4 ) 3 + Cu (unbalanced ) 2Fe + 3CuSO 4  Fe 2 (SO 4 ) 3 + 3Cu

7/6/ Fe + 3CuSO 4  Fe 2 (SO 4 ) 3 + 3Cu 2Fe + 3CuSO 4  Fe 2 (SO 4 ) 3 + 3Cu 10.1 g Fe g Fe 1 mol Fe 2 mol Fe 3 mol Cu 1 mol Cu g Cu =17.3 g Cu

7/6/ More Examples To make silicon for computer chips they use this reaction SiCl 4 + 2Mg  2MgCl 2 + Si How many grams of Mg are needed to make 9.3 g of Si? 16 g Mg

7/6/ More Examples SiCl 4 + 2Mg  2MgCl 2 + Si How many grams of SiCl 4 (MW = g/mol) are needed to make 9.3 g of Si? Answer g SiCl 4 Grams of MgCl 2 (MW 95.21) produced along with 9.3 g of silicon? Answer g MgCl 2

7/6/ For Example The U. S. Space Shuttle boosters use 3 Al(s) + 3 NH 4 ClO 4  Al 2 O 3 + AlCl NO + 6H 2 O How much Al must be used to react with 652 g of NH 4 ClO 4 (MW = g/mol)? 150 g Al. How much water is produced? Ans g H 2 O How much AlCl 3 (MW = g/mol)? 247 g AlCl 3

7/6/ Learning Check S3 4 Fe + 3 O 2 2 Fe 2 O 3 4 Fe + 3 O 2 2 Fe 2 O 3 How many grams of O 2 are needed to produce mol of Fe 2 O 3 ? 1) 38.4 g O 2 2) 19.2 g O 2 3) 1.90 g O 2 Yes!

7/6/ Solution S mol Fe 2 O 3 x 3 mol O 2 x 32.0 g O 2 2 mol Fe 2 O 3 1 mol O 2 = 19.2 g O 2

7/6/ : Limiting Reagent and Percent Yield What is a Limiting Reagent? –limiting reagent- _____ or ________ the amount of product formed; completely ______ in a rxn.; it runs out –Excess reagent- reactant not completely used up; there is plenty Ex. Sample E (pg 314) Practice 1 Limits determines used up

7/6/ Calculating the Percent Yield –theoretical yield- ________ amount of product formed; this is your ________ result or ideal amount –actual yield- amount of product actually formed from an _________ –percent yield- the ratio of the _____ yield to the _________ yield expressed as a percent –% Yield = actual yield x 100 theoretical yield theoretical yield –Ex. Sample F (p 317) & G (p318) –Practice 1 maximum calculated experiment actual theoretical