ReactionsChapter 3CombustionChapter 4 ReactionsDecompositionCombinationExchange reactions (Metathesis)• Formation of a precipitate•Formation of a gasFormation of a gas• Formation of a week or non-electrolyteSingle Displacement Reactions• Redox reactions• Oxidation numbersMary J. Bojan Chem 110 1Balancing EquationsLaw of conservation of mass: matter cannot be lost in anymatter cannot be lost in any chemical reactionMary J. Bojan Chem 110 2Patterns of reactivity•(Complete)Combustion reactions (Chapter 3)Know how to balance a chemical reaction(p)(p )C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)•Combination reactions(Chapter 3)•Combination reactions (Chapter 3)2Mg(s) + O2() 2MgO(s)(C )• Decomposition reactions (Chapter 3)PbCO3(s) PbO(s) + CO2(g)Mary J. Bojan Chem 110 3Write balanced reactions forThe combustion of ethanol CH3CH2OHThe decomposition of lead carbonate PbCO3The decomposition of lead carbonate PbCO3The combination of nitrogen and hydrogen to form ammonia (NH3)Mary J. Bojan Chem 110 4Patterns of reactivityKhtbl hilti• Exchange reactions (Chapter 4)PiittiKnow how to balance a chemical reactionPrecipitationPb(NO3)2(aq) + 2KI(aq) PbI(s) + 2KNO3(aq)NeutralizationNaOH(aq) + HCl(aq) NaCl(aq) + H2O()Gas formation2HCl(aq) + Na2S(aq) H2S(g) + 2NaCl(aq)• Single displacement reactions (Chapter 4)2Ca(s) + O2(g) 2CaO(s)Mary J. Bojan Chem 110()2(g)()5Exchange reaction(Double Displacement)(Double Displacement)Exchange positive ions to get productsAD + XZ AZ + XDExample: RttPb(NO)KIReactants: Pb(NO3)2+ KIBalance the reaction.D thi h ? TRY!Does anything happen? TRY!Do you have to do the reaction to know?Mary J. Bojan Chem 110y6Metathesis Reactions(Double Displacement)(Double Displacement)Given reactants: exchange positive ions to get productsproductsRequires a driving force (otherwise nothing happens)Dii FDriving Forces1. Precipitate forms2. Weak or nonelectrolyte forms 3. Gas formsHow do you know what is happening?Net Ionic EquationMary J. Bojan Chem 110Net Ionic Equation 7Precipitation ReactionMix silver nitrate and sodium chloride.What happens?Molecular EquationIonic EquationSpectator ions: Net Ionic EquationMary J. Bojan Chem 110 8SOLUBILITY RULES FOR COMMON IONIC COMPOUNDS IN WATER1. Almost all ammonium and alkali metal salts are soluble.2. Most nitrates, acetates, chlorides, bromides, and sulfates are soluble.Exceptions: silver halidespsulfates of Ca,Ba,Pb,Ag3Most sulfides carbonates phosphates and hydroxides3.Most sulfides, carbonates, phosphates and hydroxides are insoluble.Exceptions: alkali salts ammonium salts. (See #1 above.)See Table 4.1 of Brown, LeMay, and Bursten for a more comprehensive listing.Mary J. Bojan Chem 110 9Formation of Weak or Nonelectrolyte(neutralization reaction)Acid + base salt + waterMolecular EquationIonic EquationIonic EquationSpectator ions: Net Ionic EquationMary J. Bojan Chem 110 10PracticeWhat is the net ionic equation for the reaction between sodium hydroxide and acetic acid?What is the net ionic equation for the reaction between sodium chloride and potassium iodide?chloride and potassium iodide?Mary J. Bojan Chem 110 11GAS FORMATIONDi t d ti fCOHSNOSOExample:•Direct production of a gasCO2, H2S, NO2, SO2• Production of weak acid which decomposes.Molecular EquationNaHCO3(aq) + HCl(aq) H2CO3(aq) + NaCl(aq)CO2(g) + H2O(l)Ionic EquationNa+(aq)+HCO3(aq)+H+(aq)+Cl(aq)H2CO3(aq)+Na+(aq)+Cl(aq) Na(aq) HCO3(aq) H(aq) Cl(aq) H2CO3(aq) Na(aq) Cl(aq) Na+(aq) + Cl(aq) + CO2(g) + H2O(l)Net IonicEquationNet Ionic EquationH+(aq) + HCO3(aq) CO2(g)+ H2O(l)Mary J. Bojan Chem 110 12Single Displacement reactions(Oxidation-Reduction)(OxidationReduction)Zn(s) + CuSO4(aq) ZnSO4(aq) +Cu(s)What is oxidized? What is reduced?What is the oxidizing agent? What is the reducing agent?Ionic equation:Net ionicequationNet ionic equationMary J. Bojan Chem 110 13Rules for determining Oxidation States1.Oxidation state of atom in elemental form is zero.1.Oxidation state of atom in elemental form is zero.e.g. Cl2O2P4C(s) S82. The oxidation number of a monatomic ion equals its charge.3. Some elements have “common” oxidation numbers that can be used as reference in determining the oxidation numbers of other atoms in thereference in determining the oxidation numbers of other atoms in the compound.Alkali metals +1Alkaline earth metals +2Fluorine–1Fluorine–1H usually +1Hydrides: metal-H compounds (–1)O usually –2peroxides (–1) &superoxidespossibleperoxides (–1) & superoxidespossibleCl, Br, I almost always –14. Sum of oxidation numbers is equal to overall charge of molecule or ion:• For a neutral compound the sum of oxidation numbers equals zero.•For a polyatomic ion the sum of the oxidation numbers is equal to theFor a polyatomic ion, the sum of the oxidation numbers is equal to the charge on the ion.5. Shared electrons are assigned to the more electronegative atom of the pair: more electronegative atom will have a negative oxidation numberMary J. Bojan Chem 110more electronegative atom will have a negative oxidation number.14ActivitySeriesTable 4.5Table 4.5Will the metal element displace the atom from its compound in a reaction?Na(s) + H2O(l) Au(s) + H2O(g) ()2(g)Zn(s) + AgNO3(aq) Active metals (groups IA, IIA, Al) very reactive!Iti(i t t l )jltlDttdilInactive (inert metals):jewelry metals Do not react readilyOther metals in betweenMary J. Bojan Chem 110 15Reactions:StoichiometryReactions: Stoichiometry•Solving problems involving Chemical reactions•Solving problems involving Chemical reactions• Limiting Reactants• Solution reactionsGh i•Gas phase reactionsMary J. Bojan Chem 110 16Basics: before you start!Assume you know:• Avogadro’s numberiit!memorize it!• definition of mole• Formula weight (molar mass)g( )• the following connections (or conversions)grammolegram molegram molecules• what is meant by:ii lf lUse these along with the empirical formulamolecular formulabalanced chemical reaction to solve problems in chemistryMary J. Bojan Chem 110 17pyHow to solve problems• write the balanced chemical reaction (or process).• make connections between experimentally measured properties and the balanced equation.In other words:Given information such as mass, volume, pressure and temperaturehow can one determine quantities oftemperature,how can one determine quantities of moles/molecules?Mary J. Bojan Chem 110 18•
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