2Stoichiometry & Balancing Equations Stoichiometry & Balancing EquationsRemember we stated in the previous chapter that stoichiometry is the study of the quantitative relationships between the amounts of reactants and products in chemical reactions.We use BALANCED equations to understand stoichiometric relationships of the elements and compounds within a chemical reaction.
3The Balanced Equation 2 atoms of Al = 2 atoms of Al The Balanced Equation2Al(s) + 3Br2(l) Al2Br6(s)2mol of Al : 3mol of Br2 : 1mol of Al2Br62 atoms of Al = atoms of Al6 atoms of Br = atoms of BrThe number of the same atom of each element must be equal on each side of the equation.
4A Closer Look at the Equation A Closer Look at the Equation2Al(s) + 3Br2(l) Al2Br6(s)The chemicals on the left are the reactants and the right are the products.The coefficient in front of the chemical denotes the stoichiometric relationship.The numerical subscript represents the number of atoms present in the molecule.The letter subscripted denotes the phase of matter.
5Balancing Equations For example the following is balanced. For example the following is balanced.CH4 + 2O2 CO2 + 2H2OTry to balance the following:Fe2S3 + O2 Fe2O3 + SAl + H2SO4 Al2(SO4)3 + H2Ca + Al2Br6 CaBr2 + Al
7Types of Reactions Combination Reactions Decomposition Reactions Types of ReactionsCombination ReactionsDecomposition ReactionsDisplacement (Single-Replacement) ReactionsMetathesis (Double-Replacement) ReactionsCombustion Reactions
8Combination Reactions Combination ReactionsA combination reaction is a reaction where two substances chemically combine to form another substance.A + B AB2Na(s) + Cl2(g) 2NaCl(s)P4(s) + 6Cl2(g) 4PCl3(s)
9Decomposition Reaction Decomposition ReactionA decomposition reaction is when a single compound decomposes into two or more other substances.AB A + B2KClO3(s) 2KCl(s) + 3O2(g)2NO2(g) 2NO(g) + O2(g)
10Displacement Reaction Displacement ReactionA displacement (single replacement) reaction is a reaction where one element displaces another element.A + BC B + ACZn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)
11Metathesis ReactionA metathesis (double replacement) reaction is a reaction where two compounds switch cations to form two new compounds.A+B- + C+D- A+D- + C+B-CaCl2(aq) + Na2CO3(aq) CaCO3(s) + 2NaCl(aq)AgNO3(aq) + KCl(aq) ???
12SOLUBILITYSolubility – the amount of a substance that can be dissolved in a given quantity of solvent (like water) at a specific temperatureUnsaturated – amount of substance less than saturatedSaturated – the exact amount at solubilitySupersaturated – excess amount of substance
13How Solubility Influences Rxn How Solubility Influences RxnWhen a substance is soluble in water, it will appear with a subscript of (aq) meaning that the substance is broken up into it’s ions incorporated into the water lattice.When a substance is insoluble in water, it will be written with a subscript of (s), (l), or (g) and will precipitate out of solution.
14Solubility of Ionic Compounds in Water Soluble Compounds ExceptionsSodium, potassium, andammonium compoundsAcetates and nitratesHalides (chlorides, bromides, Lead(II), silver, and mercury (I)and iodides) halides are insolubleSulfates Calcium, strontium, barium, andLead(II) sulfates are insoluble
15Insolubility of Ionic Compounds in Water Insoluble Compounds ExceptionsCarbonates and phosphates Sodium, potassium, andammonium compoundsare soluble.Hydroxides Sodium, potassium, calcium,strontium, and barium compoundsare solubleSulfide Sodium, potassium, calcium,and ammonium compounds
16A Look at Metathesis Again A Look at Metathesis AgainLooking back at slide 10 to the first reaction: when the cations rearranged, the CaCO3 being insoluble by our definition is recorded as CaCO3 (s). The CaCO3 would precipitate out of solution as a solid.Looking at AgNO3(aq) + KCl(aq) ?, we can rearrange the cations and conclude that the AgCl is a solid and will precipitate out of solution
17Types of Metathesis Reactions Types of Metathesis ReactionsThree classifications of metathesis reactionsPrecipitation reaction - formation of a solidPb(NO3)2(aq) + Na2CO3(aq) PbCO3(s) + 2NaNO3(aq)Neutralization reaction - formation of waterHCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)Gas formation reaction - CO2, H2S, SOx, & NOx are typically formed
18Precipitation Reactions Precipitation ReactionsA solid precipitate is produced in the rearrangement of cations as follows:Pb(NO3)2(aq) + Na2CO3(aq) PbCO3(s) + 2NaNO3(aq)The Ionic Equation is expressed as:Pb+2 + 2NO3- + 2Na+ + CO3-2 PbCO3(s) + 2Na+ + 2NO3-After neglecting the spectator ions, the net ionic equation will look like:Pb+2(aq) + CO3-2(aq) PbCO3(s)
19Reviewing Ionic Compounds Reviewing Ionic CompoundsCa+2 + 2Cl- CaCl2Each ion comes together based on charge to form an overall neutral ionic compound.3Ca+2 + 2PO4-3 Ca3(PO4)2The cation and the polyatomic ion come together based on charge to form an overall neutral ionic compound.
20Net Ionic Equations (NIE) Net Ionic Equations (NIE)If you were given the reactants Ca(NO3)2 and Na3PO4 you should be able to predict the precipitate and write a balance equation, the ionic equation, and the net ionic equation (NIE) for this reaction.The NIE for these reactants is as follows:3Ca+2(aq) + 2PO4-3(aq) Ca3(PO4)2(s)
21Common Polyatomic Ions Common Polyatomic Ionscarbonate ion CO3-2sulfate ion SO4-2sulfite ion SO3-2hydroxide OH-phosphate PO4-3permanganate MnO4-chromate CrO4-2dichromate Cr2O7-2ammonium NH4+oxalate C2O4-2bicarbonate HCO3-cyanide ion CN-acetate C2H3O3-
22Neutralization Reaction Neutralization ReactionA neutralization reaction is a reaction that occurs between an acid and a base with the production of a salt and water.HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)acid base salt water
23Gas Formation Reaction Gas Formation ReactionA gas formation reaction is a metathesis reaction that generates a gas as a product.Metal carbonates or bicarbonates + acidMetal sulfides + acidMetal sulfites + acidAmmonium salts and strong base
24Metal CarbonatesMetal carbonates or bicarbonates when combined with an acid form salt, water and carbon dioxide gas.Na2CO3(aq)+ 2HCl(aq) 2NaCl(aq)+ H2O(l)+ CO2(g)Where CO2 gas is given off
25Metal SulfidesMetal sulfides when combined with an acid form salt and hydrogen sulfide gas.Na2S(aq)+ 2HCl(aq) 2NaCl(aq)+ H2S(g)Where H2S gas is given off
26Metal SulfitesMetal sulfites when combined with an acid form salt, water, and sulfur dioxide gas.Na2SO3(aq)+ 2HCl(aq) 2NaCl(aq)+ H2O(l)+ SO2(g)Where SO2 gas is given off
27Ammonium SaltsAmmonium salts when combined with a base produce salt, water and ammonia.NH4Cl (aq)+ NaOH(aq) NaCl(aq)+ H2O(l)+ NH3(g)Where ammonia gas is given off
28Combustion ReactionsA combustion reaction is a reaction with molecular oxygen to form products in which all elements are combined with oxygen.CH4 + 2O2 CO2 + 2H2O
29Limiting ReactantsOne of the reactants is in limited supply and thus restricts the amount of product formed.Think of it as: If you wanted to bake a batch of peanut butter cookies and the recipe calls for 1 cup of peanut butter and all you have is ½ a cup, even though you have all the other ingredients, you can at most make ½ a batch of cookies.
30Limiting Reactants (cont.) Limiting Reactants (cont.)Consider the combustion reaction:CH4 + 2O2 CO2 + 2H2OHow much CO2 can be produced if you have 0.13g of methane and 0.45g of O2?
31Percent YieldThe maximum amount of product that can be obtained from a chemical reaction is the theoretical yield.The actual amount produced in a chemical process is the actual yield.The percent yield is equal to the actual yield divided by the theoretical yield times 100%.
32Redox ReactionsOxidation of an element takes place when electrons are lost from the valence shell of the element.Reduction of an element takes place when electrons are added to the valence shell of the element.Redox reactions show the transfer of electrons that takes place during oxidation and reduction.
33Redox Reactions (cont.) Redox Reactions (cont.)All oxidation and reduction reactions involve transfer of electrons between substances.View CD-ROM screen 5.12Ag+ accepts electrons for Cu and is reduced to Ag and Cu loses electrons to Ag+ and is oxidized to Cu+2 in the following redox rxn:2Ag+(aq) + Cu(s) 2Ag(s) + Cu+2(aq)
34Redox Reactions (cont.) Redox Reactions (cont.)The oxidation half reaction is :Cu(s) – 2e- Cu+2(aq)The reduction half reaction is:2Ag+(aq) + 2e- 2Ag(s)Cu is called the reducing agent because it caused Ag+ to be reduced; and Ag+ is called the oxidizing agent because it caused Cu to be oxidized.
35Determining Oxidation Numbers Determining Oxidation NumbersEach atom in a pure element has an oxidation number of zero.For monoatomic ions, the ox. number is equal to it’s ionic charge.F is always –1, other halogens are –1 as well except with oxygen or fluorine.The ox. number for H is +1 except with hydrides (CaH2).and O is –2 except with peroxides (H2O2).The ox.# must = 0 for a compound or = to the overall charge of polyatomic ion being considered.
36Balancing Redox Reactions Balancing Redox ReactionsWe can use the balance of electrons transferred in a redox reaction to help us balance the overall equation.Consider the unbalanced equation:Zn(s) + HCl(aq) ZnCl2(aq) + H2(g)The balanced equation takes into consideration the oxidation of the Zn and the reduction of the H+.Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
37Molarity Molarity = Moles of Solute Liters of Total Solution MolarityMolarity = Moles of SoluteLiters of Total SolutionSymbol for molarity is MUnits are moles/Liter
38Solution PreparationTo prepare a 1.0M solution of NaCl, you would determine how many grams of NaCl is contained in 1.0 moles of NaCl and then dissolve that amount in a 1.0L volumetric flask. You would then qs with distilled H2O.1.0M NaCl = 1 mole (or 58.44g) NaCl1.0L of solutionHow much NaCl would you use to make a 0.1M solution of NaCl?As 1/10 of a mole = 5.844g NaCl, you would dissolve0.1mole (5.844g) of NaCl in 1.0L of solution.
39Acids An acid is defined as follows: Arrhenius – releases H+ when dissolved in H2OBronsted-Lowrey – a substance that can donate a proton to another substanceLewis – a substance that can accept a pair of electrons from another atom to form a new bond
40Bases A base is defined as follows: Arrhenius – releases OH- when dissolved in H2OBronsted-Lowrey – a substance that can accept a proton from another substanceLewis – a substance that can donate a pair of electrons to another atom to form a new bond
41pH and Concentrations of Acids and Bases pH = -log [H+]1 – acidic – 7 – basic – 14When dealing with [H+] less than 0.1M (pH=1), we use activity coefficients instead of pH.
42pH of Household Items pH of vinegar = 2.80 pH of soda = 2.90 pH of orange juice = 3.80pH of pure water = 7.00pH of blood = 7.40pH of ammonia = 11.00pH of oven cleaner = 11.7
43TitrationA method for quantitative analysis of a substance by essentially complete reaction in solution with a measured quantity of a reagent of known concentration.Often used in redox reactionsMany redox reactions go rapidly to completion in aqueous media to determine the equivalency point.Typically used for neutralization reactions.Acid is titrated with a base using an indicator to determine the equivalency point of the neutralization reactions.