Chemistry and Chemical Reactivity 6th Edition PDF

Chemistry and Chemical Reactivity 1 6th Edition John C. Kotz Paul M. Treichel...

Chemistry and Chemical Reactivity 1 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 4 Chemical Equations and Stoichiometry Lectures written by John Kotz © 2006 © 2006 Brooks/Cole Brooks/Cole Thomson - Thomson  2 CHEMICAL REACTIONS Chapter 4 Reactants: Zn + I2 Product: Zn I2 © 2006 Brooks/Cole - Thomson  3 Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O2(g) 2 Al2O3(s) The numbers in the front are called stoichiometric coefficients The letters (s), (g), and (l) are the physical states of compounds. © 2006 Brooks/Cole - Thomson  4 Reaction of Phosphorus with Cl2 Notice the stoichiometric coefficients and the physical states of the reactants and products. © 2006 Brooks/Cole - Thomson  5 Reaction of Iron with Cl2 Notice the stoichiometric coefficients and the physical states of the reactants and products. © 2006 Brooks/Cole - Thomson  Chemical Equations 6 4 Al(s) + 3 O2(g) 2 Al2O3(s) This equation means 4 Al atoms + 3 O2 molecules ---give---> 2 “molecules” of Al2O3 4 moles of Al + 3 moles of O2 ---give---> 2 moles of Al2O3 © 2006 Brooks/Cole - Thomson  7 Chemical Equations 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 Demo of conservation of matter, See Conservation of Screen 4.3. Matter 2HgO(s) 2 Hg(liq) + O2(g) © 2006 Brooks/Cole - Thomson  8 Chemical Equations 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. Lavoisier, 1788 © 2006 Brooks/Cole - Thomson  9 Balancing Equations ___ Al(s) + ___ Br2(liq) ___ Al2Br6(s) © 2006 Brooks/Cole - Thomson  10 Balancing Equations ____C3H8(g) + _____ O2(g) _____CO2(g) + _____ H2O(g) ____B4H10(g) + _____ O2(g) ___ B2O3(g) + _____ H2O(g) © 2006 Brooks/Cole - Thomson  11 STOICHIOMETRY - the study of the quantitative aspects of chemical reactions. © 2006 Brooks/Cole - Thomson  STOICHIOMETRY 12 It rests on the principle of the conservation of matter. 2 Al(s) + 3 Br2(liq) ------> Al2Br6(s) © 2006 Brooks/Cole - Thomson  13 PROBLEM: PROBLEM: IfIf 454 454 gg of of NH NH44NO NO33 decomposes, decomposes, how how much much NN22O O and and H H22O O are are formed? formed? What What is is the the theoretical theoretical yield yield of of products? products? © 2006 Brooks/Cole - Thomson  GENERAL GENERAL PLAN PLAN FOR FOR 14 STOICHIOMETRY STOICHIOMETRY CALCULATIONS CALCULATIONS Mass Mass reactant product Stoichiometric Moles factor Moles reactant product © 2006 Brooks/Cole - Thomson  15 454 454 gg of of NH NO33 NH44NO NN22O O ++ 22 H H22O O STEP 5 How much N2O is formed? Total mass of reactants = total mass of products 454 g NH4NO3 = ___ g N2O + 204 g H2O mass of N2O = 250. g © 2006 Brooks/Cole - Thomson  16 454 454 gg of of NH NO33 NH44NO N N22O O ++ 22 H H22O O Amounts Table (page 125) Compound NH4NO3 N2 O H2 O Initial (g) Initial (mol) Change (mol) Final (mol) Final (g) Note that matter is conserved! © 2006 Brooks/Cole - Thomson  17 454 454 gg of of NH NO33 NH44NO NN22O O ++ 22 H H22O O Amounts Table (page 125) Compound NH4NO3 N2O H2O Initial (g) 454 g 0 0 Initial (mol) 5.68 mol 0 0 Change (mol) -5.68 +5.68 +2(5.68) Final (mol) 0 5.68 11.4 Final (g) 0 250 204 Note that matter is conserved! © 2006 Brooks/Cole - Thomson  18 454 454 gg of of NH NO33 NH44NO NN22O O ++ 22 H H22O O STEP 6 Calculate the percent yield If you isolated only 131 g of N2O, what is the percent yield? This compares the theoretical (250. g) and actual (131 g) yields. © 2006 Brooks/Cole - Thomson  19 454 454 gg of of NH NO33 NH44NO NN22O O ++ 22 H H22O O STEP 6 Calculate the percent yield actual yield % yield = 100% theoretical yield © 2006 Brooks/Cole - Thomson  PROBLEM: PROBLEM: Using Using 5.00 5.00 gg of of H H22O O22,, 20 what what mass mass of of O O22 and and of of HH22O O can can be be obtained? obtained? © 2006 Brooks/Cole - Thomson  21 Reactions Involving a LIMITING REACTANT 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. © 2006 Brooks/Cole - Thomson  22 LIMITING REACTANTS Reactants Products 2 NO(g) + O2 (g) 2 NO2(g) Limiting reactant = ___________ Excess reactant = ____________ © 2006 Brooks/Cole - Thomson  23 LIMITING REACTANTS Demo of limiting reactants on Screen 4.7 © 2006 Brooks/Cole - Thomson  LIMITING REACTANTS 24 (See CD Screen 4.8) React solid Zn with 0.100 mol HCl (aq) Zn + 2 HCl ---> ZnCl2 + H2 1 2 3 Rxn 1: Balloon inflates fully, some Zn left * More than enough Zn to use up the 0.100 mol HCl Rxn 2: Balloon inflates fully, no Zn left * Right amount of each (HCl and Zn) Rxn 3: Balloon does not inflate fully, no Zn left. © 2006 Brooks/Cole - Thomson  LIMITING REACTANTS 25 React solid Zn with 0.100 mol HCl (aq) Zn + 2 HCl ---> ZnCl2 + H2 0.10 mol HCl [1 mol Zn/2 mol HCl] = 0.050 mol Zn Rxn 1 Rxn 2 Rxn 3 mass Zn (g) 7.00 3.27 1.31 mol Zn 0.107 0.050 0.020 mol HCl 0.100 0.100 0.100 mol HCl/mol Zn 0.93/1 2.00/1 5.00/1 Lim Reactant LR = HCl no LR LR = Zn © 2006 Brooks/Cole - Thomson  26 Reaction to be Studied 2 Al + 3 Cl2 Al2Cl6 © 2006 Brooks/Cole - Thomson  27 PROBLEM: PROBLEM: Mix Mix 5.40 5.40 gg of of Al Al with with 8.10 8.10 gg of of Cl Cl22.. What What mass mass ofof Al Al22Cl Cl66 can can form? form? Mass Mass reactant product Stoichiometric Moles factor Moles reactant product © 2006 Brooks/Cole - Thomson  28 Step Step 11 of of LR LR problem: problem: Find Find the the limiting limiting reactant. reactant. © 2006 Brooks/Cole - Thomson  29 Step Step 22 of of LR LR problem: problem: Use Use the the limiting limiting reactant reactant as as your your basis basis for for the the stoichiometry stoichiometry calculation. calculation. © 2006 Brooks/Cole - Thomson  30 How How much much of of which which reactant reactant will will remain remain when when reaction reaction is is complete? complete? Cl2 was the limiting reactant. Therefore, Al was present in excess. But how much? First find how much Al was required. Then find how much Al is in excess. © 2006 Brooks/Cole - Thomson  31 Chemical Analysis Active Figure 4.8 © 2006 Brooks/Cole - Thomson  32 Chemical Analysis An impure sample of the mineral thenardite contains Na2SO4. Mass of mineral sample = 0.123 g The Na2SO4 in the sample is converted to insoluble BaSO4. The mass of BaSO4 is 0.177 g What is the mass percent of Na2SO4 in the mineral? © 2006 Brooks/Cole - Thomson  33 Chemical Analysis Na2SO4(aq) + BaCl2(aq) 2 NaCl(aq) + BaSO4(s) 0.177 g BaSO4 (1 mol/233.4 g) = 7.58 x 10-4 mol BaSO4 7.58 x 10-4 mol BaSO4 (1 mol Na2SO4/1 mol BaSO4) = 7.58 x 10-4 mol Na2SO4 7.58 x 10-4 mol Na2SO4 (142.0 g/1 mol) = 0.108 g Na2SO4 (0.108 g Na2SO4/0.123 g sample)100% = 87.6% Na2SO4 © 2006 Brooks/Cole - Thomson  34 Determining the Formula of a Hydrocarbon by Combustion Active Figure 4.9 © 2006 Brooks/Cole - Thomson  Using Stoichiometry to 35 Determine a Formula Burn 0.115 g of a hydrocarbon, CxHy, and produce 0.379 g of CO2 and 0.1035 g of H2O. CxHy + some oxygen 0.379 g CO2 + 0.1035 g H2O What is the empirical formula of CxHy? © 2006 Brooks/Cole - Thomson  Using Stoichiometry to 36 Determine a Formula CxHy + some oxygen ---> 0.379 g CO2 + 0.1035 g H2O First, recognize that all C in CO2 and all H in H2O is from CxHy. +O2 0.379 g CO2 1 CO2 molecule forms for Puddle of CxHy each C atom in CxHy 0.115 g +O2 0.1035 g H2O 1 H2O molecule forms for each 2 H atoms in CxHy © 2006 Brooks/Cole - Thomson  Using Stoichiometry to 37 Determine a Formula CxHy + some oxygen ---> 0.379 g CO2 + 0.1035 g H2O First, recognize that all C in CO2 and all H in H2O is from CxHy. 1. Calculate amount of C in CO2 2. Calculate amount of H in H2O © 2006 Brooks/Cole - Thomson  Using Stoichiometry to 38 Determine a Formula CxHy + some oxygen ---> 0.379 g CO2 + 0.1035 g H2O Now find ratio of mol H/mol C to find values of x and y in CxHy. © 2006 Brooks/Cole - Thomson