Presentation on theme: "Chapter 4 Stoichiometry"— Presentation transcript:
1 Chapter 4 Stoichiometry Chemical ReactionsChapter 4Stoichiometry
2 Chemical Equations 4 Al (s) + 3 O2 (g) 2 Al2O3 (s) A chemical reaction shows the formulas and relative amounts of reactants and products in a reaction.4 Al (s) O2 (g) 2 Al2O3 (s)reactantsproductstoichiometriccoefficientsphysical states, l, g or aq
3 Chemical Equations 4 Al (s) + 3 O2 (g) 2 Al2O3 (s) Interpret this equation as4 atoms solid Al react with 3 molecules gaseous O2 to form 2 formula units of solid Al2O34 moles solid Al react with 3 moles gaseous O2 to form 2 moles of solid Al2O3
4 Balancing Chemical Equations “Matter is conserved inchemical change”Antoine Lavoisier, 1789An equation must be balanced:It must have the same numberof atoms of each kind on both sides
5 The rules of the gameWrite the correct formulas of the reactants and productsDo not change the formulas to balance the equationPut a coefficient in front of each formula so that the same number of atoms of each kind appear in both the reactants and productsThe coefficent multiplies through its formula2 H2O shows 4 H atoms and 2 O atoms
6 Combustion ReactionsIn combustion, a hydrocarbon or C–H–O fuel combines with O2 to form CO2 and H2O__ CH4 + __ O2 __ CO2 + __ H2O1 CH O2 1 CO H2OBalanced equation shows 1 C, 4 H, and 4 O on each sideIf N or S are in the formula for the fuel, assume it is oxidized to NO2 or SO2
7 Example 4-1Write a balanced equation for the complete combustion of ethylene, C2H4.Write and balanced equation for the complete combustion of thiophene, C4H4S
8 Example 4-2Write a balanced equation for the complete combustion of glycerol, C3H8O3Write a balanced equation for the complete combustion of thiosalicylic acid, C7H6O2S
9 Stoichiometry Stoichiometry is chemical accounting The heart of stoichiometry is the mole ratio given by the coefficients of the balanced equation
10 Stoichiometry Stoichiometry is chemical accounting The heart of stoichiometry is the mole ratio given by the coefficients of the balanced equationmoles Amole ratiomoles Bmoles Amoles B
11 Example 4-3AHow many moles of O2 are produced form the decomposition of 1.76 mol potassium chlorate: 2 KClO3 (s) 2 KCl (s) + 3 O2 (g)
12 Example 4-3BHow many moles of Ag are produced in the decomposition of 1.00 kg of silver (I) oxide: 2 Ag2O (s) 4 Ag (s) + O2 (g)
13 Example 4-4AHow many grams of magnesium nitride are produced when 3.82 g Mg react with excess N2: 3 Mg (s) + N2 (g) Mg3N2 (s)
14 Example 4-4BHow many grams of H2 (g) are needed to produce 1.00 kg of CH3OH: CO (g) H2 (g) CH3OH (l)
15 Example 4-5AHow many grams of H2 are consumed per gram of O2 in the reaction 2 H2 (g) + O2 (g) 2 H2O (l)
16 Example 4-5BHow many grams of O2 are consumed per gram of octane (C8H18) in the combustion of octane?
17 2 Al (s) + 6 HCl (aq) 2 AlCl3 (aq) + 3 H2 (g) Example 4-6AThe model problem describes an Al-Cu alloy composed of 93.7% Al and 6.3% Cu by mass, with a density of 2.85 g/cm3. The Al (but not the Cu) reacts with HCl:2 Al (s) HCl (aq) 2 AlCl3 (aq) H2 (g)What volume of the Al-Cu alloy must be dissolved in HCl to produce 1.00 g H2?
18 2 Al (s) + 6 HCl (aq) 2 AlCl3 (aq) + 3 H2 (g) Example 4-6BThe model problem describes an Al-Cu alloy composed of 93.7% Al and 6.3% Cu by mass, with a density of 2.85 g/cm3. The Al (but not the Cu) reacts with HCl:2 Al (s) HCl (aq) 2 AlCl3 (aq) H2 (g)How many grams of Cu are present in a sample of alloy that yields 1.31 g H2 when it reacts with HCl?
19 Example 4-7AThe model problem describes an HCl solution which is 28% HCl by mass and has a density of 1.14 g/mL. It reacts with Al: Al (s) HCl (aq) 2 AlCl3 (aq) H2 (g)How many mg of H2 are produced when 1 drop (0.05 mL) of the HCl solution reacts with Al?
20 Example 4-7BA vinegar contains 4.0% HC2H3O2 by mass and has a density of 1.01 g/mL. It reacts with sodium hydrogen carbonate: HC2H3O2 (aq) + NaHCO3 (s) NaC2H3O2 (aq) + H2O (l) + CO2 (g)How many grams of CO2 are produced by the reaction of 5.00 mL of this vinegar with NaHCO3?
21 Chemical Reactions in Solution Most reactions occur in aqueous solutionSOLUTE is the substance to be dissolved in solutionSOLVENT is the substance (often a liquid) the solute dissolves inThe concentration of the solution is Molarity (M) = moles solute L solution
22 Example 4-8AIf 22.3 g acetone, (CH3)2CO, are dissolved in enough water to make 1.25 L of solution, what is the concentration (M) of the solution?
23 Example 4-8B15.0 mL of concentrated acetic acid, HC2H3O2 (d = g/mL), are dissolved in enough water to produce mL of solution. What is the concentration of the solution?
24 Example 4-9AAt 25 °C, an aqueous solution saturated with NaNO3 is 10.8 M NaNO3. How many grams of NaNO3 are present in 125 mL of this solution?
25 Example 4-9BHow many grams of Na2SO4 • 10 H2O are needed to prepare 355 mL of M Na2SO4?
26 Dilution problemsIt is common to prepare a solution by diluting a more concentrated solution (the stock solution).The moles of solute taken from the stock solution are given by moles solute = volume x molarityAll the solute taken from the stock appears in the diluted solution, so moles solute are constant: VstockMstock = VdiluteMdilute
27 Example 4-10A15.00 mL of M K2CrO4 solution are diluted to mL. What is the concentration of the dilute solution?
28 Example 4-10BAfter being left out in an open beaker, 275 mL of M NaCl has evaporated to only 237 mL. What is the concentration of the solution after evaporation?
29 Stoichiometry in Solution Stoichiometry in solution is just the same as for mass problems, except the conversion into or out of moles uses molarity instead of molar mass:grams AmL Amoles Amoles Bgrams BmL Bmole ratio
30 Example 4-11AK2CrO4 (aq) + 2 AgNO3 (aq) Ag2CrO4 (s) + 2 KNO3 (aq)How many mL of M K2CrO4 must react with excess AgNO3 to produce 1.50 g Ag2CrO4?
31 Example 4-11BK2CrO4 (aq) + 2 AgNO3 (aq) Ag2CrO4 (s) + 2 KNO3 (aq)How many mL of M AgNO3 must react with excess K2CrO4 to produce exactly 1.00 g Ag2CrO4?
32 Limiting reactantIn a given reaction, often there is not enough of one reactant to use up the other reactant completelyThe reactant in short supply LIMITS the quantity of product that can be formed
34 Goldilocks ChemistryImagine reacting different amounts of Zn with mol HCl: Zn (s) HCl (aq) ZnCl2 (aq) + H2 (g)Rxn 1 Rxn 2 Rxn 3Mass Zn g g gMoles Zn mol mol molMoles HCl mol mol molRatio mol HClmol Zn
35 Limiting reactant problems The easiest way to do these is to do two stoichiometry calculationsFind the amount of product possible from each reactantThe smaller answer is the amount of product you can actually make (you just ran out of one reactant)The reactant on which that answer was based is the limiting reactant
36 Example 4-12AHow many grams of PCl3 form when 215 g P4 react with 725 g Cl2: P4 (s) Cl2 (g) 4 PCl3 (l)
37 Example 4-12BHow many kg of POCl3 form if 1.00 kg of each reactant are allowed to react: PCl3 (l) + 6 Cl2 (g) + P4O10 (s) 10 POCl3 (l)
38 Example 4-13A When 215 g P4 react with 725 g Cl2 P4 (s) Cl2 (g) 4 PCl3 (l) (example 4-12A)which reactant is in excess and what mass of that reactant remains after the reaction is finished?
39 Example 4-13B12.2 g H2 and 154 g O2 are allowed to react. Identify the limiting reactant, which gas remains after the reaction, and what mass of it is left over. 2 H2 (g) + O2 (g) 2 H2O (l)
40 Percent YieldIn real experiments we often do not get the amount of product we calculate we should, becausethe reactants may participate in other reactions (side reactions) that produce other products (by-products)The reaction often does not go to completion.Percent yield tells the ratio of actual to theoretical amount formed.
41 Percent YieldSuppose you calculate that a reaction will produce 50.0 g of product. This is the theoretical yield.The reaction actually produces only 45.0 g of product . This is the actual yield.Percent yield = g (actual) x 100 = 90.0% g (theoretical)
42 Example 4-14AIf 25.7 g CH2O is produced per mole CH3OH that reacts, what are the theoretical, actual, and percent yield: CH3OH (g) CH2O (g) + H2 (g)
43 Example 4-14BWhat is the percent yield if 25.0 g P4 reacts with 91.5 g Cl2 to produce 104 g PCl3: P4 (s) Cl2 (g) 4 PCl3 (l)
44 Example 4-15AIf the observed percent yield for the formation of urea is 87.5%, what mass of CO2 must react with excess NH3 to produce 50.0 g CO(NH2)2: NH3 (g) + CO2 (g) CO(NH2)2 (s) + H2O (l)
45 Example 4-15BWhat mass of C6H11OH should you start with to produce 45.0 g C6H10 if the reaction has 86.2% yield and the C6H11OH is 92.3% pure: C6H11OH (l) C6H H2O (l)
46 Exercise 26 Balance these equations by inspection (NH4)2Cr2O7 (s) Cr2O3 (s) + N2 (g) + H2O (g)NO2 (g) + H2O (l) HNO3 (aq) + NO (g)H2S (g) + SO2 (g) S (g) + H2O (g)SO2Cl2 + HI H2S + H2O + HCl + I2
47 Exercise 30 Write balanced equations for these reactions: Sulfur dioxide gas with oxygen gas to produce sulfur trioxide gasSolid calcium carbonate with water and dissolved carbon dioxide to produce aqueous calcium hydrogen carbonateAmmonia gas and nitrogen monoxide gas to produce nitrogen gas and water vapor
48 Exercise 32 3 Fe (s) + 4 H2O (g) Fe3O4 (s) + H2 (g) How many moles of H2 can be produced from 42.7 g Fe and excess steam?How many grams of H2O are consumed in the conversion of 63.5 g Fe to Fe3O4?If 7.36 mol H2 are produced, how many grams of Fe3O4 must also be produced?
49 Exercise 36Silver oxide decomposes above 300 °C to yield metallic silver and oxygen gas g impure silver oxide yields g O2. Assuming there is no other source of O2, what is the % Ag2O by mass in the original sample?
50 Exercise 42How many grams of CO2 are produced in the complete combustion of 406 g of a bottled gas that consists of 72.7% C3H8 (propane) and 27.3% C4H10 (butane), by mass?
51 Exercise 45 What are the molarities of these solutes? 150.0 g sucrose (C12H22O11) in mL aqueous solution98.3 mg of 97.9% pure urea, CO(NH2)2, in 5.00 mL aqueous solutionmL methanol (CH3OH, density = g/mL) in 15.0 L aqueous solution
52 Exercise 52After 25.0 mL of aqueous HCl solution is diluted to mL, the concentration of the diluted solution is found to be M HCl. What was the concentration of the original HCl solution?
53 Exercise 56 Ca(OH)2 (s) + 2 HCl (aq) CaCl2 (aq) + 2 H2O (l) How many grams of Ca(OH)2 will react completely with 415 mL of M HCl?How many kilograms of Ca(OH)2 will react with 324 L of an HCl solution that is 24.28% HCl by mass, density = 1.12 g/mL?
54 Exercise 63g oxalic acid, H2C2O4, is exactly neutralized by mL of a NaOH solution. What is the concentration of the NaOH solution? H2C2O NaOH Na2C2O H2O
55 Exercise 70Chlorine can be generated by heating calcium hypochlorite and hydrochloric acid to form chlorine gas, calcium chloride, and water. If 50.0 g Ca(OCl)2 and 275 mL 6.00 M HCl react, how many grams of Cl2 gas form? Which reactant is left over, and how much (in grams)?
56 Exercise 722 C6H5NO2 + 4 C6H14O4 (C6H5N)2 + 4 C6H12O4 + 4 H2Onitrobenzene triethylene azobenzene glycolIf 0.10 L nitrobenzene (d = 1.20 g/mL) react with 0.30 L triethylene glycol (d = 1.12 g/mL) to form 55 g azobenzene, findTheoretical yieldActual yieldPercent yield