A voltaic cell consists of a Zn/Zn2+ half-cell and a Ni/Ni2+ half-cell at 25 oC. The initial concentrations of Ni2+ and Zn2+ are 1.50 M and 0.100 M, respectively.
a. What is the initial cell potential?
b. What is the cell potential when the concentration of Ni2+ has fallen to 0.500 M?
c. What are the concentrations of Ni2+ and Zn2+ when the cell potential falls to 0.45 V?
Angel Carrasquillo CHM 132 Notes Week of 01/24/31 ● Hess’s Law - The total enthalpy is the sum of all changes. Enthalpy is a state function. - ΔHrxn = ΣΔH products - ΣΔH rectants ● ΔHrxn from Bond Dissociation Energy - Bond break absorbs energy - Bond make releases energy - BDE (+) is a homolytic bond cleavage - So… H----H →H + H - each H has its own electron when bond is broken - ΔHrxn = ΣΔH broken - ΣΔH formed (bonds broken and formed) ● Entropy (S) - Organization of energy - spread of energy → ↑entropy ΔS= (+) - Favorable ● Isothermal - Reversal: Rxn always at equilibrium, work put in=work put out, at equilibrium no energy lost or gained. - Irreversible: Work is heat, E conversion from ordered to disordered ● qrev = -wrev = nRTln(V2/V1) - ΔE= 0 qnet(wrev)=0 - S = Kb(lnΩ) Ω= microstate Kb= R/NA - ↑S is favorable ● 3rd Law of Thermodynamics - S = 0 for perfect crystal at 0 K - absolute energy can be calculated ● For ideal gases - ΔS = nR*ln(V2/V1) ● 2nd law of thermodynamics - spontaneous forward rxn - ΔSuniverse = (+) = ΔSrxn + ΔSsurroundings ● ↑Temp results in ΔS = (+) - increase in entropy for increase in temp - for gas, ↑V = ΔS (+) - and increase in # gas molecules = ΔS (+) ● ΔHrxn (-) is related to ΔSsurroundings - ΔSsurroundings = -ΔHrxn/T - ΔSuniverse = ΔSsurrounding + ΔSrxn….if (+), then forward rxn is spontaneous ● with Δ Hrxn and ΔSrxn, ΔSuniverse is (+), there
