# Dr. S. M. Condren Chapter 4 Chemical Equations and Stoichiometry.

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Dr. S. M. Condren Chapter 4 Chemical Equations and Stoichiometry

Dr. S. M. Condren CHEMICAL REACTIONS Reactants: Zn + I 2 Product: Zn I 2

Dr. S. M. Condren Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) The numbers in the front are called stoichiometric coefficients The letters (s), (g), and (l) are the physical states of compounds, (aq) refers to an aqueous or water solution.

Dr. S. M. Condren The Mole and Chemical Reactions: The Nano-Macro Connection 2 H 2 + O 2 -----> 2 H 2 O 2 H 2 molecules 1 O 2 molecule 2 H 2 O molecules 2 H 2 moles molecules 1 O 2 mole molecules 2 H 2 O moles molecules 4 g H 2 32 g O 2 36 g H 2 O

Dr. S. M. Condren Stoichiometry stoi·chi·om·e·try noun 1. Calculation of the quantities of reactants and products in a chemical reaction. 2. The quantitative relationship between reactants and products in a chemical reaction.

Dr. S. M. Condren 4 Al(s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) This equation means 4 Al atoms + 3 O 2 molecules ---give---> 2 molecules of Al 2 O 3 4 moles of Al + 3 moles of O 2 ---give---> 2 moles of Al 2 O 3 Chemical Equations

Dr. S. M. Condren Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change. The Law of the Conservation of Matter Demo of conservation of matter 2HgO(s) ---> 2 Hg(liq) + O 2 (g) Chemical Equations

Dr. S. M. Condren Combination Reaction PbNO 3(aq) + K 2 CrO 4(aq) PbCrO 4(s) + 2 KNO 3(aq) Colorless yellow yellow colorless

Dr. S. M. Condren Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Chemical Equations Lavoisier, 1788

Dr. S. M. Condren ___ Al(s) + ___ Br 2 (liq) ---> ___ Al 2 Br 6 (s) Balancing Equations

Dr. S. M. Condren ____C 3 H 8 (g) + _____ O 2 (g) ----> _____CO 2 (g) + _____ H 2 O(g) ____B 4 H 10 (g) + _____ O 2 (g) ----> ___ B 2 O 3 (g) + _____ H 2 O(g) Balancing Equations

Dr. S. M. Condren EXAMPLE How much H 2 O, in moles results from burning an excess of H 2 in 3.3 moles of O 2 ? H 2 + O 2 -----> H 2 O #mol H 2 O = 22 (3.3 mol O 2 )(2 mol H 2 O) (1 mol O 2 ) Now we need the stoichiometric factor = 6.6 mol H 2 O

Dr. S. M. Condren Stoichiometric Roadmap

Dr. S. M. Condren EXAMPLE How much H 2 O, in grams results from burning an excess of H 2 in 3.3 moles of O 2 ? H 2 + O 2 -----> H 2 O #g H 2 O = 22 (3.3 mol O 2 )(2 mol H 2 O) (1 mol O 2 ) = 1.2x10 2 g H 2 O (18.0 g H 2 O) (1 mol H 2 O)

Dr. S. M. Condren EXAMPLE How much H 2 O, in grams results from burning an excess of H 2 in 3.3 grams of O 2 ? H 2 + O 2 -----> H 2 O #g H 2 O = 22 (1 mol O 2 )(2 mol H 2 O) (1 mol O 2 ) = 3.7 g H 2 O (18.0 g H 2 O) (1 mol H 2 O) (3.3 g O 2 ) (32.g O 2 )

Dr. S. M. Condren Thermite Reaction

Dr. S. M. Condren Thermite Reaction Fe 2 O 3(s) + 2Al (s) Al 2 O 3(s) + 2 Fe (l)

Dr. S. M. Condren Thermite Reaction

Dr. S. M. Condren EXAMPLE How much iron(III) oxide and aluminum powder are required to field weld the ends of two rails together?

Dr. S. M. Condren EXAMPLE How much iron(III) oxide and aluminum powder are required to field weld the ends of two rails together? Assume that the rail is 132 lb/yard and that one inch of the rails will be covered by an additional 10% mass of iron. The mass of iron in 1 inch of this rail is: #g/in = (132 #/yard) (1 yard/36 in) (454 g/#) = 1.67 X 10 3 g/in The mass of iron in a weld adding 10% mass: #g = (1.67 X 10 3 g) (0.10) = 167 g

Dr. S. M. Condren EXAMPLE How much iron(III) oxide and aluminum powder are required to field weld the ends of two rails together? The mass of iron in a weld adding 10% mass: #g = (1.67 X 103 g) (0.10) = 167 g Balanced chemical equation: Fe 2 O 3 + 2 Al ---> 2 Fe + Al 2 O 3 What mass of Fe 2 O 3 is required for the thermite process? #g Fe 2 O 3 = (167 g Fe) (1 mol Fe) ---------------- (55.85 g Fe) (1 mol Fe 2 O 3 ) ------------------- (2 mol Fe) (159.7 g Fe 2 O 3 ) ---------------------- (1 mol Fe 2 O 3 ) = 238 g Fe 2 O 3

Dr. S. M. Condren EXAMPLE How much iron(III) oxide and aluminum powder are required to field weld the ends of two rails together? The mass of iron in a weld adding 10% mass: #g = (1.67 X 103 g) (0.10) = 167 g Balanced chemical equation: Fe 2 O 3 + 2 Al ---> 2 Fe + Al 2 O 3 What mass of Al is required for the thermite process? #g Al = (167 g Fe) (1 mol Fe) ---------------- (55.85 g Fe) (2 mol Al) -------------- (2 mol Fe) (26.9815 g Al) ------------------- (1 mol Al) = 80.6 g Al

Dr. S. M. Condren EXAMPLE How much iron(III) oxide and aluminum powder are required to field weld the ends of two rails together? Assume that the rail is 132 lb/yard and that one inch of the rails will be covered by an additonal 10% mass of iron. The mass of iron in a weld adding 10% mass: #g Fe = 167 g Fe #g Fe 2 O 3 = 238 g Fe 2 O 3 #g Al = 80.6 g Al

Dr. S. M. Condren In a given reaction, there is not enough of one reagent to use up the other reagent completely.In a given reaction, there is not enough of one reagent to use up the other reagent completely. The reagent in short supply LIMITS the quantity of product that can be formed.The reagent in short supply LIMITS the quantity of product that can be formed. Reactions Involving a LIMITING REACTANT

Dr. S. M. Condren LIMITING REACTANTS eactants R eactantsProducts 2 NO(g) + O 2 (g) 2 NO 2 (g) Limiting reactant = ___________ Excess reactant = ____________

Dr. S. M. Condren EXAMPLE What is the number of moles of Fe(OH) 3 (S) that can be produced by allowing 1.0 mol Fe 2 S 3, 2.0 mol H 2 O, and 3.0 mol O 2 to react? 2Fe 2 S 3(S) + 6H 2 O (l) + 3O 2(g) -----> 4Fe(OH) 3(S) + 6S (S) balanced equation relates: 2Fe 2 S 3(S) 6H 2 O (l) 3O 2(g) have only: 1Fe 2 S 3 (S) 2H 2 O (l) 3O 2(g) not enough H 2 O to use all Fe 2 S 3 plenty of O 2

Dr. S. M. Condren EXAMPLE What is the number of moles of Fe(OH) 3 (S) that can be produced by allowing 1.0 mol Fe 2 S 3, 2.0 mol H 2 O, and 3.0 mol O 2 to react? 2Fe 2 S 3(S) + 6H 2 O (l) + 3O 2(g) -----> 4Fe(OH) 3(S) + 6S (S) if use all Fe 2 S 3 : (1.0 mol Fe 2 S 3 ) (4 mol Fe(OH) 3 ) #mol Fe(OH) 3 = ------------------------------------------ (2 mol Fe 2 S 3 ) = 2.0 mol Fe(OH) 3

Dr. S. M. Condren EXAMPLE: What is the number of moles of Fe(OH) 3 (S) that can be produced by allowing 1.0 mol Fe 2 S 3, 2.0 mol H 2 O, and 3.0 mol O 2 to react? 2Fe 2 S 3(S) + 6H 2 O (l) + 3O 2(g) -----> 4Fe(OH) 3(S) + 6S (S) if use all H 2 O: (2.0 mol H 2 O) (4 mol Fe(OH) 3 ) #mol Fe(OH) 3 = ----------------------------------------- (6 mol H 2 O) = 1.3 mol Fe(OH) 3

Dr. S. M. Condren EXAMPLE: What is the number of moles of Fe(OH) 3 (S) that can be produced by allowing 1.0 mol Fe 2 S 3, 2.0 mol H 2 O, and 3.0 mol O 2 to react? 2Fe 2 S 3(S) + 6H 2 O (l) + 3O 2(g) -----> 4Fe(OH) 3(S) + 6S (S) if use all O 2 (3.0 mol O 2 ) (4 mol Fe(OH) 3 ) #mol Fe(OH) 3 = --------------------------------------- (3 mol O 2 ) = 4.0 mol Fe(OH) 3

Dr. S. M. Condren EXAMPLE: What is the number of moles of Fe(OH) 3 (S) that can be produced by allowing 1.0 mol Fe 2 S 3, 2.0 mol H 2 O, and 3.0 mol O 2 to react? 2Fe 2 S 3(S) + 6H 2 O (l) + 3O 2(g) -----> 4Fe(OH) 3(S) + 6S (S) 1.0 mol Fe 2 S 3 => 2.0 mol Fe(OH) 3 2.0 mol H 2 O => 1.3 mol Fe(OH) 3 3.0 mol O 2 => 4.0 mol Fe(OH) 3 least amount Since 2.0 mol H 2 O will produce only 1.3 mol Fe(OH) 3, then H 2 O is the limiting reactant. Thus the maximum number of moles of Fe(OH) 3 that can be produced by this reaction is 1.3 moles.

Dr. S. M. Condren Theoretical Yield the amount of product produced by a reaction based on the amount of the limiting reactant

Dr. S. M. Condren Actual Yield amount of product actually produced in a reaction

Dr. S. M. Condren Percent Yield actual yield % yield = --------------------- * 100 theoretical yield

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00 kg Cl 2 ) #kg N 2 H 4 = ---------------------

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00 kg Cl 2 ) (1000 g Cl 2 ) #kg N 2 H 4 = ----------------------------------- (1 kg Cl 2 ) metric conversion

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00) (1000 g Cl 2 ) (1 mol Cl 2 ) #kg N 2 H 4 = ----------------------------------------- (1) (70.9 g Cl 2 ) molar mass

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00)(1000)(1 mol Cl 2 ) #kg N 2 H 4 = ----------------------------------------- (1)(70.9)

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00)(1000)(1 mol Cl 2 )(1 mol N 2 H 4 ) #kg N 2 H 4 = ------------------------------------------------- (1) (70.9) (1 mol Cl 2 )

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00)(1000)(1)(1 mol N 2 H 4 ) #kg N 2 H 4 = ------------------------------------------------- (1) (70.9)(1)

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00)(1000)(1)(1 mol N 2 H 4 ) (32.0 g N 2 H 4 ) #kg N 2 H 4 = -------------------------------------------------------- (1)(70.9) (1) (1 mol N 2 H 4 ) molar mass

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00)(1000)(1)(1) (32.0 g N 2 H 4 )(1 kg N 2 H 4 ) #kg N 2 H 4 = ---------------------------------------------------------- (1)(70.9)(1)(1) (1000 g N 2 H 4 ) metric conversion

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00)(1000)(1)(1) (32.0)(1 kg N 2 H 4 ) #kg N 2 H 4 = ---------------------------------------------------------- (1)(70.9)(1)(1)(1000)

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) to calculate the theoretical yield, use the net equation for the overall process (1.00)(1000)(1)(1) (32.0)(1 kg N 2 H 4 ) #kg N 2 H 4 = ---------------------------------------------------------- (1)(70.9)(1)(1)(1000) = 0.451 kg N 2 H 4

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) theoretical yield#kg N 2 H 4 = 0.451 kg N 2 H 4 (b) actual yield (0.299 kg product) # kg N 2 H 4 = --------------------------

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) theoretical yield#kg N 2 H 4 = 0.451 kg N 2 H 4 (b) actual yield (0.299 kg product) (98.0 kg N 2 H 4 ) # kg N 2 H 4 = -------------------------------------------- (100 kg product) purity factor

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) theoretical yield#kg N 2 H 4 = 0.451 kg N 2 H 4 (b) actual yield (0.299 kg product) (98.0 kg N 2 H 4 ) # kg N 2 H 4 = -------------------------------------------- (100 kg product) = 0.293 kg N 2 H 4

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) theoretical yield#kg N 2 H 4 = 0.451 kg N 2 H 4 (b) actual yield# kg N 2 H 4 = 0.293 kg N 2 H 4

Dr. S. M. Condren EXAMPLE A chemical plant obtained 0.299 kg of 98.0% N 2 H 4 for every 1.00 kg of Cl 2 that is reacted with excess NaOH and NH 3. What are the: (a) theoretical, (b) actual, and (c) percent yield of pure N 2 H 4 ? 2NaOH + Cl 2 + 2NH 3 -----> N 2 H 4 + 2NaCl + 2H 2 O (a) theoretical yield#kg N 2 H 4 = 0.451 kg N 2 H 4 (b) actual yield# kg N 2 H 4 = 0.293 kg N 2 H 4 (c) percent yield 0.293 kg % yield = -------------- X 100 = 65.0 % yield 0.451kg

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