CHEM 1120 1nd EditionExam # 3 Study Guide Chapters 19, 20, 24Chapter 19 Word or Concept Definition/Explanation Spontaneous process A chemical or physical change that is thermodynamically favored by nature (i.e. ball rolling downhill), does not mean it is fast, can be temperature dependent, not all spontaneous processes are exothermicReversible process A process that can be reversed by an infinitesimalchange in a variable, returns both system and surrounding to their original stateIrreversible process Process which is not a reversible process, can only return system to its original state but not thesurroundings2nd Law of Thermodynamics ΔS(universe) = ΔS (system) + ΔS(surroundings) > 0, for reversible process = 0, for irreversible > 0Entropy Measure of disorder in a system, measure of the extent to which a system’s energy is not available to do work, S = k x ln(W), S = q (rev) / T“Positional” Entropy A gas will spontaneously expand into a vacuum, probability: (1/2)^n where n is number of moleculesEntropy as energy disposal Energy will try to disperse over a large number of particles and energy levelsS = k x ln(W) W = number of possible microstatesK = Boltzmann constant = 1.381 x 10^-23 J/KEntropy and Solutions Usually when a solid is dissolved in a solvent, entropy increasesEntropy of perfect crystal at 0 K is… Equal to 0Standard Molar Entropies (So) Positive for pure substances, doesn’t = 0, So gas >So liquid > So solid, higher molar mass = higherSo, More atoms in molecule = higher SoΔSo = Sum of So products – Sum of So reactants Same for Gibbs free energy except use ΔGoΔS (universe) = ΔS (rxn) – ΔH (rxn) / T When T and P are constantG = H – TS State functionSpontaneity and Gibbs Free Energy Negative: forward reaction spontaneous, 0: at equilibrium, Positive: Reverse reaction spontaneous ΔG = w max Equals maximum useful work that can be done bythe system at constant T and PΔG = ΔGo + RTlnQ Q = value of equilibrium expression under ANY conditionsΔGo = -RTlnK At equilibrium Chapter 20Word or Concept Definition/Explanation Electrochemistry Relationship between chemical change and electrical workElectrochemical cell Systems that incorporate a redox reaction to produce or utilize cell energyDoes work by releasing energy from spontaneous reactionDoes work by absorbing energy from a source of electricityOxidation Loss of electronsReduction Gain of electronsOxidizing agent Species that does the oxidizing-taking electrons from substance being oxidized (gets reduced)Reducing agent Species that does the reducing-giving electrons tosubstance being reduced (gets oxidized)Half-Reaction Method (Acids) 1. Separate into 2 half-cells2. Balance all elements except O and H,balance O using H20, balance H using H+, balance charge using e-3. Multiply by factors to equate e- loss and gain4. Add balanced half reactions Half-Reaction Method (Bases) 1. Balance as if it were acidic (steps 1-4 above)2. Neutralize H+ by adding OH- to both sides3. Cancel H2O where necessary Voltaic Cell (galvanic cell) Uses spontaneous chemical reaction to produce electrical energyElectrolytic cell Uses electrical energy to drive a non-spontaneousreaction (ΔG >0)Anode Where oxidation occurs, Zn  Zn2+ + 2e-Cathode Where reduction occurs 2e- + Cu2+  CuElectron flow Leave anode and flow through wire into cathode, as electrons reach cathode, cations are attracted to now negative cathode, Voltaic Cell notation Oxidation on left; reduction on right, vertical line implies a phase boundary, double vertical line implies a salt bridge (Not all voltaic cells have salt bridges, could have porous barrier) Cell potential Electrical potential difference between 2 half cells, also called voltage, electromotive force (emf), or Ecell, for spontaneous reaction >0 Difference between 2 electrodesStandard cell potential (Eocell) Cell potential when operated under standard conditions (1 atm, 1M, pure liquids and solids, and usually 298 K) = Eo (cathode) – Eo (anode) More positive = cathodeVolt SI unit of potential, =1 J/CΔG = -nFEcell or ΔGo = -nFEocell n=moles of electrons transferredF=Faraday=9.65 x 10^4 C/mol=charge of a moleof electronsEocell = RT/nF lnKeq Ecell = Eocell – RT/nF ln Q R = 8.314 J/mol K, T=temp in Kelvin, n=moles of electrons transferred, F=9.65 x 10^4, Q=reaction quotientFuel cells Convert hydrogen and oxygen into electricity and heat, no recharging, not a batteryCorrosion of Iron Iron dissolves (anodic region), Fe2O3.H20 (rust) created, needs airCathodic protection Make iron behave more like cathode (use galvanized steel coated with a sacrificial layer of zinc zinc oxidized instead of iron) Electrolytic cell Energy from an external source drives a nonspontaneous reaction Overvoltage Difference between the actual cell potential required for appreciable electrolysis and the calculated cell potential Chapter 24Alkanes Single covalent bondAlkenes At least one double bondAlkynes At least on triple bondAromatics Contain rings with delocalized electrons Acyclic alkanes No rings, CnH2n+2, saturated hydrocarbons, Condensed structure Atoms usually drawn next to atoms to which they are bonded, parentheses are used around similar groups bonded to the same atomSkeletal structurs Carbon atom at junction of any two line or end ofline, assume enough hydrogens around each carbon to make it tetravalent, draw in heteroatomsStructural isomers Same molecular formula, different bondconnectivitiesCyclic alkanes Contain only C and H in single covalent bonds, at least one ring, CnH2nClassification of Carbon atoms Primary: bonded to one other carbon, secondary:2 other carbons, tertiary: 3 other carbons, quaternary: 4 other carbons Naming Prefix: location and name of substituentsRoot: number of carbons in longest chain, suffix: what familyNaming alkanes -ane, name longest continuous chain, number thelongest chain starting at end nearest a substituent, name each substituent (alkyl group), use di, tri, tetra if 2 or more alkyl groups are identical, list alkyl groups in alphabetical order 10 roots based on number of carbons 1-meth, 2-eth, 3-prop, 4-but, 5-pent, 6-hex, 7-hept, 8-oct, 9-non, 10-decAlkyle groups Carbon substituent bonded to a long carbon chain, formed by removing one H from an alkane,to name change –ane of parent to –yl Reactions of Alkanes Rather unreactive, make great nonpolar solvents, undergo combustion reactionsAcyclic Alkenes Contain at least 1 double bond, no rings, CnH2n,