-Gain Electrons Reduction (rhe study of the inserciianq. of chemical and eledncal energy.) Applications of Redox - Reduction Involves Gain (of electrons) -Lose Electrons Oxidation LEO - GER Chapter 17: Electrochemistry -Oxidation Involves Loss (of electrons) Review egen dwge zero k..pwi.nei I to Wi, 00w tot tram - oxidizing from I agere to oni flow reducrg 0ra4wwe Bridge r flow Salt (A device in ietwch dtemical energy is changed to etocl,to.l.ner) Galvanic Cell doing useful work, but if separate 2, 5(Fe Fe 8H+MnO 4+5&, Mn 2 +4H 20 (reduction) reactions Helps to break the reactions into half 3 + e) (oxidation) 8H+MnO+ 5Fg 2 +5e Mri 2 + 5Fe 3 +41170 Moving electrons electric current In the same mixture it happens without Applications Page 1 F +2 e Electricity travels in a complete circuit builds up BUT stops immediately because charge Connected this way the reaction starts L) jrj 4J ),:_4- Lj.)( transfer of electrons Oxidation reduction reactions involve a OIL - RiG
Page 2 2 2 + E0 Cu 2 (aq) *Zn 2(aq) + Cu(s) - Measured with a voltmeter.i.*i.t - Also H2i aa1bcqe Disk iijft4 so change its sign j One of the reactions must be reversed atm 1 M solutions states of 25 C, 1 table (Table 17.1, p. 827 & Appendix 5.5) Indicates standard t& We can look up reduction potentials in a are compared to.j j potential at each electrode all other oxidations H2in This is the reference The total cell potential is the sum of the Standard Hydrogen Electrode Zn(s) + Cu Cell Potential equal loijoule of worklcoulomb of charge called the electromotive lorce (ami) s the cell potential Oxidizing agent pushes the electron The push or pull (dnving torcen) is called Cell Potential j O.76yJ Reducing agent pulls the electron 1_Fe gentl +2.- - Anode Cathode P1.I.ebo C (for 2W 2-iH..... E = E0. Zn Cu d instead Porous e Sometimes a porous
reacting inert conductor) is indicated Double line = porous disk or salt bridge aqueous, a platinum electrode (non- if all the substances on one side are is intensive) Single line = different phases half reaction is multiplied by an integer (E0 Anode on the left I I Cathode on the right The value of E isn t changed when the. Solid I Aqueous I IAqueous I Solid Page 3 Rici*r, 2ceJ I ( 4.4A4 I ilfr (AV -In fact, reverse is spontaneous (spontaneous) spontaneous) ec lf E < 0, then G > 0 (not I;r u-ni c4 ts lf E > 0, then G < 0 change in E from Le Chátelier.G = -nfe (for standard conditions) Qualitatively - can predict direction of Concentration Potential, Work and \G Cell Potential and (electrodes and ions); line notation 3. Designation of anode and cathode. w = -qe = -rife = tg (because zg = maximum 2. Direction of flow q = rif = moles of e x charge/mole e 4. Nature of all the components useful work obtainable from the process) 1. Cell Potential (always +) & the -w = qe Four things for a complete description Charge is measured in coulombs cell potential E = balanced cell reaction Faraday = 96,485 Clmol r in the direction that produces a positive E = work done by system I charge The reaction always runs spontaneously. emf potential (V) work (J) I Charge (C) Galvanic Cell Potential, Work and zg 1) Cell Potential Line Notation
-rife = -rife + RT1n(Q) E = E EJJn(Q) Reach equilibrium where Q = K and products increase and reactants decrease = G +RT)n(Q) As reactions proceed concentrations of Page 4 2 H20 + 4e, 4 OH- (Cathode) Reaction happens in two places (RUST) Iron Dissolves: Fe -. Fe 2. eiaiiode) 4Fe 2.O2+(4.2n)H 2O,nH 2O+8H E 0.84 V 20 2Fe ( 02 21420 4e. 401t E= 0.40 V 2+2e -.Fe E 044V Fe potentials that are less positive than 02 Most structural metals have reduction ithepfoceuutwflbewnk&ts-or8s) conductivity Water Spontaneous oxidation bepn,n.no up process by increasing 2 + Cd + 2HO Ni0 Zn. 2NH, + 2MnO driving force. Dry Cell NiCad Zn+2MnO 2, ZnOMn 2O2 (In base) Alkaline reaction has reached equilibrium and there s no longer a chemical 2-.Zn 2 (s)+2h50 Pb(s)+Pb0 4(s).2H 20 (1) 4-.2H -.2PbSO Car batteries are lead storage batteries A dead* battery is when the cell (more commonly a group ol galvanic cells in series) Batteries are Galvanic Cells 2 2NH 3+H20+Mn 20, from voltage we can tell concentration RT 00592 lf concentration can give voltage, then = ln(k) at 25C log K: balancing n nf -.0592 log(q) at 25C Always have to figure out n by 1E = RT1n(K) p Cd(OH) 2 +NI(OH) 7 0 E RTIn(K) rip The Nernst Equation The Nernst Equation
more easily oxidized that get oxidized instead pieces of an active metal like magnesium (by the car s alternator) Cathodic Protection - Attaching large Used for electroplating, charging a battery Galvanizing - Putting on a zinc coat Has a tower reduction potential, so it is Alloying with metals that form oxide coats and reverse the direction of the redox reaction Running a galvanic cell backwards Put a voltage bigger than the potential (electrolytic cell) paint or metal plating) change bc which the cam potential Is negative) (forcing a current though a cell to produce a chemical Electrolysis Have to count charge.1 amp = 1 coulomb of charge per second q/nf moles of metal Mass of plated metal q I x Measure current, I (in amperes) Calculating Plating ;;r +cda JcJñ Z.:- ::.: 1.OM 1 Coating to keep out air and water (like Preventing Corrosion Page 5 Jc. -:> 4 G Hc 14 4 C L/ I ( Q HC) the reaction proceeds fprward WO (Prwu Electrolysis of water Separating mixtures of ions More positive reduction potential means Other Uses cl CtL a- - E\c-rc c Cathode Anode 44e e-