2 Chocolate Chip Cookie Recipe Makes 42 cookies ½ c butter½ c brown sugar½ c granulated sugar1 egg½ tsp vanilla1 cup flour½ tsp salt½ tsp baking soda½ c chopped walnuts½ c chocolate chipsWhat is the product of this recipe?How would you adjust the ingredients in the recipe to make 7 dozen cookies?What would you do if you only had ¼ c butter?
3 Stoichiometry Mass-mass relationships Quantitative study of chemical reactions
4 Balanced Equations give us: the relationship between the reactants and the productsthe ratios in which they combineThe coefficients represent the number of moles2 H2 + 1 O2 2 H202 moles of hydrogen react w/ 1 mole of oxygen to form 2 moles of water
5 Law of Conservation of Mass Basis behind stoichiometryMass of reactants= mass of productEx. 4Fe + 3O2 2 Fe2O34 moles of iron react w/ 3 moles of oxygen to form 2 moles of rustConvert moles to grams4 moles Fe55.8 g Fe= g Fe1mole FeTotal mass of reactants: g3 moles O232.0 g O2= g O21 mole O2
6 Mass of reactants= mass of products 2 moles Fe2O3158.7 g Fe2O3= g Fe2O3(mass of products)1 mole Fe2O3Mass of reactants= mass of products
7 Trail MixIn order to make trail mix, you need raisins, peanuts, and M&M's. What makes it good trail mix is having the right ratios! In the bags there are 1 dozen raisins (R), 2 dozen peanuts (P), and 3 dozen M&M's (MM). This is a perfect combination to make 1 package of trail mix (TM).If we were to write an equation to represent this recipe it would look like this:1 dozen raisins + 2 dozen peanuts + 3 dozen M&M's = 1 trail mixor 1 R + 2 P + 3 MM 1 TM
8 1 R + 2 P + 3 MM1 TMWith this in mind, what if you only had ½ the contents of your bags…How many dozen peanuts would you need to mix them with 1/2 dozen raisins?By looking at the equation, you can come up with a conversion of 2 dozen peanuts for every 1 dozen raisins.SO…½ dozen raisins x 2 dozen peanuts = 1 dozen peanuts needed 1 dozen raisins (or ½ your bag!)(Just like halving a recipe!)
9 1 R + 2 P + 3 MM1 TMHow many dozen M&M's would you need to combine them with 6 dozen peanuts?3 dozen MM6 dozen peanut2 dozen peanuts9 dozen m &m’s
10 1 R + 2 P + 3 MM1 TMHow many dozen raisins would you need to mix with 4 dozen peanuts?4 dozen peanut1 dozen raisin2 dozen peanut= 2 dozen raisins
11 1 R + 2 P + 3 MM1 TMHow many dozen peanuts would you need to mix them with 18 M&M's?(careful!)2 dozen peanuts18 mm’s1 dozen mm3 dozen mm’s12 mm’s1 dozen peanuts
12 Chemists use ratios such as these ALL the time in the laboratory Chemists use ratios such as these ALL the time in the laboratory. Instead of dozens, they use moles – something we've already looked at. Just as in the equation above, the coefficients in front of the compounds provide the "mole ratios" the chemists need.
13 Mole RatiosRatio between the numbers of moles of any 2 substances in a balanced equationYou can have many different ratio scenarios for each equation
14 2 Al + 3 Cl2 2 AlCl3 Ratio of Al to Cl 2 moles Al 3 moles Cl Ratio of Cl to Al 3 moles Cl2 moles AlRatio of Cl to product 3 moles Cl2 moles AlCl3Ratio of product to Cl 2 moles AlCl3Ratio of Al to product 2 moles AlRatio of product to Al 2 moles AlCl3
15 Stoichiometry Answers these ?’s: How much of 1 reactant is needed to combine w/ a given amount of another reactantHow much product will be produced w/ a given amount of reactantHow much reactant is needed to produce a given amount of product
16 Steps in Stoichiometry Write the balanced equationWrite the given information under the equation (molar mass, # of moles, grams of known)Convert grams of known substance to moles using molar mass
17 Determine the mole ratio using the coefficients from balanced equation moles of unknownmoles of known5. Convert the moles of unknown to grams using molar mass
18 known moles (molar mass unknown) g unknown Known mass g (from problem) unknown moles1 mole knowng known(molar mass known)known moles( coef. from eqn.)1 mole unknown
19 How many grams of AlCl3 are produced if 3 How many grams of AlCl3 are produced if 3.0g of Cl2 react with excess aluminum?1.) Balanced Equation:2 Al Cl2 2 AlCl33.0 g3 mole Cl271.0 g/mole? g2 moles AlCl3133.5 g/mole2.) Write in known info
20 3. Convert known grams to moles, put in mole ratio (from coefficients) and convert unknown moles to grams.3.0g Cl22 moles AlCl3133.5 g AlCl31 mole Cl23 moles Cl21 mole AlCl371.0 g Cl2(Mass known)(Molar mass known)(Mole Ratio)(molar mass unknown)
21 3. Multiply the top line and divide by the bottom (making sure to use parentheses correctly) (3.0 x 2 x )(71.0 x 3)= g of AlCl3 formed
22 Stoichiometry of Shuttle Launch NASA TV (Discovery Last Launch)You Tube (STS 119)
23 Percent YieldQuantities found in stoichiometry are theoretical or predicted amounts (the amount you are supposed to get if all the conditions are perfect)During actual experimentation, you will come up w/ less than expected% Yield = actual amt (experiment) x 100Theoretical amt (calculated)
24 You calculated that you should get 82. 2g of NaCl in a reaction You calculated that you should get 82.2g of NaCl in a reaction. When you performed the experiment you produced only 30.7 g NaCl. What is your % yield?% Yield = x 10082.237.3%
25 Limiting Reactant (reagent) Reactant that is totally consumed during a reactionLimits the extent of a reactionDetermines the amount of product that can be formedOnce it is gone, the reaction stops
26 Excess Reactant (reagent) Reactant that remains after the reaction stops
28 Steps:Balance equationUsing known amounts of each reactant, solve for mass of product (do 2 separate stoichiometry problems)The one that produces the least amount of product is the limiting reactant.
29 Balance equation and write in known info 75 g of CaO react with 30.0 g HCl to produce calcium chloride and water. What is the limiting reactant? How much water is formed?Balance equation and write in known infoCaO HCl CaCl H2075 g1 mole56.1 g/mole30.0 g2 mole36.5 g/mole? g1 mole18.0 g/mole
30 Do 2 stoichiometry problems, w/ each reactant as a known and the unknown being water 1 mole H2O18.0 g H2O75 g CaO1 mole CaO1 mole CaO1 mole H2O56.1 g CaO=24 g H2O
31 Do 2 stoichiometry problems, w/ each reactant as a known and the unknown being water 1 mole H2O18.0 g H2O30.0 g HCl1 mole HCl2 mole HCl1 mole H2O36.5 g HCl7.40 g H2O
32 HCl is the limiting reactant, producing 7.40 g of water CaO is in excess (meaning some will be left over after the reaction)
33 Finding mass of excess reactant that remains: One can find the mass of excess reactants that will remain by doing another stoichiometry problem using your limiting reactant as your known and the excess reactant as your unknownMass excess starting- mass excess used (stoich. Calc)= mass of left over excess react.
34 Using HCl as the known and CaO as the unknown, calc. the amt Using HCl as the known and CaO as the unknown, calc. the amt. Of CaO used.30.0 g HCl mole HCl 1 mole CaO g CaO36.5 g HCl 2 mole HCl mole CaO=23.1 CaO used75 g CaO – 23.1g used = 51.9 g leftover
35 N H2 2 NH3If you have g of N2 and 25.0 g of H2, which is your limiting reactant in the reaction?How many grams of NH3 can be produced from that limiting reactant?Calculate the mass of excess reactant that remains after the reaction is complete.
37 Practical application of stoichiometry Calculationsmole ratiosLaw of conservation of massStoichiometryLimiting reactant problem% yieldEssayPractical application of stoichiometry
38 4HCl + O2 2 H2O + 2 Cl2 Interpret it in terms of moles What is the mole ratio between water and oxygen?Show that mass is conserved
39 _ Cu + _ AgNO3 _ Cu(NO3)2 + _ Ag Balance the equationHow many grams of copper are needed to react with 12.0 g of AgNO3?
40 _ Al + _ Cl2 __AlCl3 Balance If you begin with 3.2 g of aluminum and 5.4g of chlorine what is the limiting reactant?
41 __Mg+ _ HCl _MgCl2 + _ H2 Balance If you reacted 10.0g of magnesium with excess hydrochloric acid. How many grams of MgCl2 will be formed?After actually reacting this you formed 29.5 g of MgCl2, what is the percent yield?