Page 1 Stoichiometry Chapter 9

Page 2 Stoichiometry Quantitative relationship between two substances Composition stoichiometry: mass relationships of elements in compounds Reaction stoichiometry: mass relationships between reactants and products

Page 3 Mole ratio Used in all reaction stoichiometry problems Gets us from given to unknown Conversion factor –Relates amounts in moles for any two substances in a reaction

Page 4 CH 4 (g) + 2O 2 (g)  2H 2 O(g) + CO 2 (g)

Page 5 Mole ratios Are exact Do not limit the number of significant figures

Page 6 Molar mass Used in many stoichiometry problems Mass in grams of one mole of a substance

Page 7 Moles to moles Amount of given substance in moles To Amount of unknown substance in moles Given amount in moles Moles of given from equation Moles of unknown from equation (mole ratio) = unknown amount in moles

Page 8 Moles to mass Given in moles To Unknown in moles To Unknown in grams Given amount in moles Moles of given from equation Moles of unknown from equation (mole ratio) 1 mole of unknown Grams of unknown (molar mass) = unknown amount in grams

Page 9 Mass to moles Given in grams To Given in moles To Unknown in moles Given amount in grams Grams of given 1 mole of given (mole ratio) Moles of given from equation Moles of unknown from equation (molar mass) = unknown amount in moles

Page 10 Mass to mass Given in grams To Given in moles To Unknown in moles To Unknown in grams Given amount in grams Grams of given 1 mole of given (mole ratio) Moles of given from equation Moles of unknown from equation (molar mass) = unknown amount in grams 1 mole of unknown Grams of unknown (molar mass)

Page 11 Carry units through All the way through the problem g and mol Elements or compounds –This saves a lot of confusion

Page 12 Moles to moles - example The elements lithium and oxygen react to form lithium oxide, Li 2 O. How many moles of lithium oxide will form if 2.0 mol of lithium react? Li + O 2  Li 2 O 4Li + O 2  2Li 2 O

Page 13 You try The disinfectant hydrogen peroxide H 2 O 2 decomposes to form water and oxygen gas. How many moles of O 2 will result from the decomposition of 5.0 mol of hydrogen peroxide? H 2 O 2  H 2 O + O 2 2H 2 O 2  2H 2 O + O 2

Page 14 Moles to mass When sodium azide is activated in an automobile airbag, nitrogen gas and sodium are produced according to the equation: 2NaN 3 (s)  2Na(s) + 3N 2 (g) If mol of NaN 3 react, what mass in grams of nitrogen would result?

Page 15 You try Coal can be converted to methane gas by a process called coal gasification. The equation for the reaction is: 2C(s) + 2H 2 O(l)  CH 4 (g) + CO 2 (g) What mass in grams of carbon is required to react with water to form 1.00 mol CH 4 ?

Page 16 You try Using the previous reaction, what mass in grams of water is required to produce 1.00 mol CH 4 ? 2C(s) + 2H 2 O(l)  CH 4 (g) + CO 2 (g)

Page 17 Mass to moles Chlorine gas can be produced commercially by passing an electric current through a concentrated solution of sodium chloride. 2NaCl(aq) + 2H 2 O(l)  2NaOH(aq) + Cl 2 (g) + H 2 (g) If the solution contains 250 g of NaCl, how many moles of Cl 2 can be produced?

Page 18 You try Using the previous reaction, how many moles of H 2 can be produced from 250 g of NaCl? 2NaCl(aq) + 2H 2 O(l)  2NaOH(aq) + Cl 2 (g) + H 2 (g)

Page 19 Mass to mass Sodium peroxide reacts vigorously with water to produce sodium hydroxide and oxygen. 2Na 2 O 2 (s) + 2H 2 O(l)  4NaOH(aq) + O 2 (g) What mass in grams of O 2 is produced when 50.0 g of Na 2 O 2 react?

Page 20 You try Using the previous reaction, what mass in grams of water is needed to react with 50.0 g of Na 2 O 2 ? 2Na 2 O 2 (s) + 2H 2 O(l)  4NaOH(aq) + O 2 (g)

Page 21 You try Milk of magnesia, a suspension of Mg(OH) 2 in water, reacts with stomach acid, HCl. Mg(OH) 2 (s) + 2HCl(aq)  2H 2 O(l) + MgCl 2 (aq) What mass in grams of HCl is required to react with 3.00 g of Mg(OH) 2 ?

Page 22 Limiting reactant AKA limiting reagent The reactant that runs out first in a reaction Limits the amounts of other reactants that will be used –And the amounts of products that will be produced.

Page 23 Examples In a game of musical chairs, what is the limiting reactant? –Number of chairs If you have 8 hot dog buns and 10 hot dogs, what is the limiting reactant? –Number of buns

Page 24 Excess reactant Not completely used up in a reaction

Page 25 Example Methanol is synthesized according to the following equation. If 500 mol of CO and 750 mol of H 2 are present, which is the limiting reactant? How many moles of methanol are produced? CO(g) + 2H 2 (g)  CH 3 OH

Page 26 You try Zinc citrate is synthesized according the following reaction. If there are 6 mol of ZnCO 3 and 10 mol of C 6 H 8 O 7, which is the limiting reactant? How many moles of Zn 3 (C 6 H 5 O 7 ) 2 will be produced? 3ZnCO 3 (s) + 2C 6 H 8 O 7 (aq)  Zn 3 (C 6 H 5 O 7 ) 2 (aq) + 3H 2 O(l) + 3CO 2 (g)

Page 27 Example Aspirin is synthesized by the reaction of salicylic acid with acetic anhydride. When 20.0 g of C 7 H 6 O 3 and 20.0g of C 4 H 6 O 3 react, which is the limiting reagent? What mass in grams of aspirin is formed? 2C 7 H 6 O 3 + C 4 H 6 O 3  2C 9 H 8 O 4 + H 2 O

Page 28 You try The unbalanced equation for the reaction of calcium phosphate with sulfuric acid is as follows: Ca 3 (PO 4 ) 2 + H 2 SO 4  CaSO 4 + H 3 PO 4 If 250 g of Ca 3 (PO 4 ) 2 react with 3 mol of H 2 SO 4, will 3 mol of CaSO 4 be formed? Why or why not?

Page 29 Theoretical yield The maximum amount of a product that can be produced from a given amount of reactant. “in theory” how much you can get

Page 30 Actual yield Always less than theoretical yield The measured amount of product What you actually get

Page 31 Percent yield Shows efficiency of a reaction Ratio of actual yield to theoretical yield

Page 32 You try The calculated theoretical yield for a reaction is 87.2 g. The measured actual yield is 82.3 g. What is the percent yield?

Page 33 Example Huge quantities of sulfur dioxide are produced from zinc sulfide by means of the following reaction. If the typical yield is 86.78%, how many grams of SO 2 should be expected if 4897 g of ZnS are used? 2ZnS + 3O 2  2ZnO + 2SO 2