2BellringerWrite the quantities of ingredients you would use to make a bologna and cheese sandwich.Then determine how many sandwiches you could make from 24 slices of bread.Calculate how much of each ingredient is needed.
3Balanced Equations Show Proportions Coefficients show the proportions of the reactants and products.2H2 + O2 2H2OCalculations involving chemical reactions use these proportions to find amounts of reactants and products.Use models to demonstrate this reaction and show the molecules.Tell students to assume:**For each problem in this section, assume that there is more than enough of all other reactants to completely react with the reactant given.**Also assume that every reaction happens perfectly, so that no product is lost during collection.
4Relative amounts in equations can be expressed in moles Coefficients represent the moles of each substance.2H2 + O2 2H2O2 mol H2 +1 mol O2 form 2 mol H2O.
5Stoichiometry You can determine: amount of reactant needed, oramount of product formedThis proportional relationship between chemical coefficients is called stoichiometry.
6OH, CHEMISTRY Verse 1 We started something new called stoichiometry. (THE STOICHIOMETRY SONG)Sung to the tune of "Jingle Bells.“Lyrics by: Brandi Abbott1992Verse We started something newcalled stoichiometry.It's such a funny word.It brings a smile to me.The first step’s not so hard.It's something that is old.You take the grams that's given thereand convert them into moles.
7You have to really know your stuff for stoichiometry! Chorus Ooooooh Chemistry, chemistry,How exciting it can be!You have to really know yourstuff for stoichiometry!(REPEAT)
8It really doesn’t boast. You put the moles in a ratio Verse The second step's not big.It really doesn’t boast.You put the moles in a ratioTo show least over most.When grams are what you seeka third step must be used.The least known's weight per molewill provide the final clue!
9Always, the same 3 steps Grams Moles Molar Ratio Coeff. of what you wantCoeff. of what you haveOnly if ans. is to be in gramsMolecular weight of what you want1 mole
10Mass- MassWhat mass of hydrogen will be used when 14 g of nitrogen gas is reacted to produce ammonia gas?N H2 2NH314 g x14 g N2 1mol N mol H g H = 3 g H228 g N mol N mol H2grams to moles least/most least known's weightper mol
11Mole-MassHow many grams of sodium will be required to react with sufficient chlorine in order to produce 4.50 moles of NaCl?2Na Cl2 2NaClx mol4.50 mol NaCl 2 mol Na g Na = g Na2 mol NaCl 1 mol Namoles least/most least known's weight(given) per mol
12Moles to Moles 2H2 + O2 2H2O 6.00 mol H2O 2 mol H2 = 6.00 mol H2 6.00 moles of water vapor are required to assist oxygen delivery in surgical ventilators. How many moles of hydrogen and how many moles of oxygen must be introduced from the gas tanks in order to insure this amount?2H2 + O2 2H2Ox y mol6.00 mol H2O 2 mol H2 = 6.00 mol H22 mol H2Omoles least/most6.00 mol H2O 1 mol O2 = 3.00 mol O2
14Limiting Reactants According to the periodic table 2Na + Cl2 2NaCl 46 g g gReactions do not always react perfectly.TemperatureAgeHumidity100% of expected product rarely achieved.
15Major PROBLEM in Industry Companies must produce enoughproduct to supply their customers.They MUST use enough reactants to fill their orders WITHOUT producing excessive overagestored ($ lost), orthrown away ($ lost)
17Industry adds an EXCESS of the cheapest reactant. Reactant that is completely consumed (used up) in the rxn.LIMITING REACTANTThe limiting reactant’s value is used for all stoichiometry calculations.
18Too Much Info!How many moles of salt can be produced from the amounts of reactants given in the following equation?2Na Cl2 2NaCl46 g g ?Too much informationone number gives reliable product information.one number lies!
19In our example2Na Cl2 2NaCl46 g g ?CALCULATE the amount of product from each amount…46 g of sodium can produce 117 g of salt91 g of chlorine can produce g of saltTherefore,Sodium is the limiting reactant and 117 g is the maximum amount of product that can be made.
20Check Both NumbersThe calculation with the smaller answer is the correct product calculation and used the limiting reactant as its ‘have’ value.
21How many grams of the excess reactant are ‘left over?’ First determine how many grams of Cl2 were used.2Na Cl2 2NaCl46 g x46 g Na 1 mol Na 1 mol Cl g Cl2 = 71 g Cl2 used23 g Na 2 mol Na 1 mol Cl2Subtract the amount used from the total amount present.[91 g present] - [71 g used] = 20 g Cl2 left over Θ
22Percent YieldThe amount of product actually produced as compared to the possible (calculated) amount.% = Actual Amount or Actual AmountPossible Amount Stoich Answer
23Sample CalculationWhen 45.8 g of potassium carbonate are reacted completely w/ excess HCl, 46.3 g of potassium chloride are produced. Water and carbon dioxide are also produced. Calculate both the theoretical and % yield.K2CO HCl 2KCl H2O CO245.8 g xTheoretical (Stoich)45.8 g K2CO3 1 mol K2CO3 2 mol KCl g KCl = g KCl138 g K2CO3 1 mol K2CO3 1 mol KCl% Yield46.3 g KCl x = % actual yield stated in question49.1 g KCl
24Mass - Energy Calculations Balanced equations can be used to determine the amt. of energy absorbed / released during the reaction. Treat energy as if it were a reactant or product.Heat of Reaction - qrIf qr is (-) then products have less energy than the reactants - exothermicIf qr is (+) then products have more energy than the reactants-endothermic.
25Sample CalculationGiven:2Na2O2 + 2H2O 4NaOH + O kJHow much E is released when 1.99 g of Na2O2 is reacted?1.99 Na2O mol Kj = 2.75 Kj.78.0 g molqr = negative, exothermic rxnqr = Kj