CHEM 1211 Lecture 8Outline of Last Lecture I. Balancing Chemical EquationsA. Law of Conservation of MatterII. Classification of SolutesA. Aqueous SolutionsB. Two Classes of Solutes1. Electrolytes2. Non-ElectrolytesIII. Chemical ReactionsOutline of Current Lecture I. Chemical EquilibriaII. Types of Reactions A. Precipitation B. Acid-Base NeutralizationC. Gas FormingD. Reduction-OxidationIII. Classifying RXNsCurrent LectureI. Chemical Equilibria- Chemical RXNs always proceed spontaneously toward equilibriumA. Dynamic Equilibrium: rate of forward rxn = rate of reverse rxn - Looks like nothing is happeningB. Product-Favored Rxn: reactants are completely or largely converted to products, reactions proceed to products- Most combustion Rxns: CH4 + 2O2  CO2 + 2H2OC. Reactant-Favored Rxn: only a small amount of reactant is converted to product - Weak AcidsII. Types of Reactions A. Precipitation: A rxn where an insoluble solid (precipitate) forms and drops out of the solution - Exchange, double displacement, or metathesis rxns- A precipitation produces a water insoluble product, known as a precipitate- Example: Formula unit equation:AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)Total ionic equations: Write the formula unit eqn in ionic form. Only ionize strong acids/bases and soluble salts (need to know solubility rules). Cannot write as ions if (s), (l), or (g)Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)  AgCl (s) + K+ (aq) + NO3- (aq)Net ionic equations: Remove spectator ions from both sides.A spectator ion is one that doesn’t participate in the reaction. Ag+ (aq) + Cl- (aq)  AgCl (s)B. Acid-Base Neutralization: A rxn in which an acid reacts with a base to yield a salt plus water- M HCl in stomach- Drano: solid NaOH with some Al chips- Organic acids (carboxylic acids) occur in nature (acetic acid –vinegar)- There are 2 commonly used definitions of acids and bases: 1. Arrhenius2. Bronsted-Lowry- Arrhenius Theory:Acid: substance that contains hydrogen and produces H+ in aqueous solutionAcid Examples HCl (aq) + H2O (l)  H3O+ (aq) + Cl- (aq) HCO2H (aq) + H2O (l) H3O+ (aq) + HCO2- (aq) Base: substance that contains hydroxyl, OH, group and produces hydroxide ions, OH-, in aqueous solutions.Base Examples NaOH (aq)  Na+ (aq) + OH- (aq) Ba(OH)2 (aq)  Ba2+ (aq) + 2 OH- (aq) - Hydronium Ion:Hydrated hydrogen ion (H+(aq))- protons generated in acid-base reactions surrounded by solvent water molecules- number of water molecules depends on solution - H+(aq) is really H(H2O)n+ - write hydrated hydrogen ion as H3O+ - called hydronium ionStrong Acids and Bases: Essentailly 100% ionized in aq solnWeak Acids and Bases: Usually < 10% ionized in aq soln- Bronsted-Lowry Theory:More general acid-base theory- acid is proton (H+) donor - base is proton (H+) acceptorExamples HBr (aq) + H2O (l)  H3O+ (aq) + Br- (aq) acid baseNH3 (aq) + H2O (l) NH4+ (aq) + HO- (aq) base acid- Bronsted-Lowry Acid-Base Reactions- transfer of a proton from an acid to a base - Example HCl (aq) + NH3 (aq) NH4+ (aq) + Cl- (aq) acid base- Coordinate covalent bonds: bonds in which both electrons are supplied by one atom are made in Bronsted-Lowry acid-base reactions- Bronsted-Lowry Conjugate Acid-Base pairs:- two species that differ by a proton- Example:HNO3 + H2O  H3O+ + NO3- conjugate acid 1 conjugate base 2 conjugate acid 2 conjugate base 1 HNO3 is the conjugate acid and NO3- is its conjugate base H2O is the conjugate base and H3O+ is its conjugate acid - Amphiprotic: a molecule (species) can act as an acid and a base. Examples: 1. H2O and NH32. H2O + H+  H3O+3. H2O  H+ +OH-4. NH3 + H+  NH4+5. NH3  H+ + NH2-- Acid-Base Theory Comparison:Major differences between Arrhenius & Bronsted-Lowry:For Brønsted-Lowry theory:- The reaction does not have to occur in an aqueous solution- Bases are not required to be hydroxides- Example: Acid-Base (neutralization) Reactionsformation of the nonelectrolyte H2O acid + base  salt + water- Oxides of Nonmetals and Metals:- Oxides of nonmetals:Acidic oxides since they react with H2O to form acidsOften called acid anhydrides- Oxides of metals: Basic oxides since the react with water to form basesOften called base anhydridesC. Gas Forming: A rxn where an insoluble gas is formed- Gas-forming reaction: Insoluble or slightly soluble gas formed when there are no gaseous reactants.- Formula unit eqn:2 HCl (aq) + CaCO3 (s)  H2CO3 (aq) + CaCl2 (aq) CO2 (g) + H2O (l)- Total Ionic2 H+ (aq) + 2 Cl- (aq) + CaCO3 (s)  H2CO3 (aq) + Ca2+ (aq) + 2Cl- (aq)- Net Ionic2 H+ (aq) + CaCO3 (s)  H2CO3 (aq) + Ca2+ (aq)D. Reduction-Oxidation: A rxn where electrons are transferred from one reactant to another- Oxidation: increase in oxidation number- corresponds to loss of electrons- Reduction: decrease in oxidation number [reduces ON]- corresponds to gain of electrons- Oxidizing agents: chemical species that oxidize some substance- contain atoms that are reduced in the reaction - gain electrons - Reducing agents: chemical species that reduce some substance - contain atoms that are oxidized in the reaction- lose electrons - ExamplesKMnO4 and Fe 2+ : Fe2+ added to purple KMnO4Fe2+ is oxidized to Fe3+ Fe2+, Fe3+ are colorless; Mn2+ is colorlessMnO41- is reduced to Mn2+ [ON of Mn in MnO41- is +7]8H+ + 5Fe2+ +MnO41-  5Fe3+ + Mn2+ + 4H2O- Assigning Oxidation NumbersExample 1: NaNO3Example 2: K2Sn(OH)6- Which species are oxidized and reduced?- Which species are oxidized and reduced?- What are the oxidizing and reducing agents?- formula unit:2 H2SO3 (aq) + O2 (g)  2 H2SO4 (aq) - Oxidation numbers? H= +1 S= +4 O= -2 O= 0 H= +1 S= +6 O= -2SO32- is oxidized [S from +4 to +6]; O2 is reduced [O from 0 to -2]H2SO3 is reducing agent; O2 is oxidizing agentIII. Classifying RXNs- Precipitation reaction: ions in reactants combine to form insoluble reaction product- Acid-base reaction: water is often product; cation and anion combine to form salt- Gas-forming reaction: gas leaves solution; often involve carbonates, sulfites of sulfides - Oxidation-reduction: Electron