Chem 430- SEM432- Homework 1 Student name: ID: Part I: True or false questions. 1- The charge transfer between an electr

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Chem 430 Sem432 Homework 1 Student Name Id Part I True Or False Questions 1 The Charge Transfer Between An Electr 1 (111.42 KiB) Viewed 42 times

Chem 430- SEM432- Homework 1 Student name: ID: Part I: True or false questions. 1- The charge transfer between an electrode and electroactive specics becomes thermodynamically Ravourable which the Fermi- level is above the LUMO of the reactant|0|. 2- The cathodic reaction rate becomes faster when the applied potential is more positive. 3- The overpotential (n) is the potential applied to the working electrode relative to the redox equilibrium potential. [ 1 4- If the effect of the potential change is un-identical on both anodic and cathodic current, then a = 0.5. [ ] 5- The Tafel slope is an intensive parameter and does not depend on the electrode surface area. 6- The exchange current (I.) is the current at equilibrium is an intensive parameter and is not influenced by the electrode surface area and the kinetics or speed of the reaction. 7- The anodic polarisation is achicved when the polcrilial is set more posilive than the Ecm. [ 1 8- In galvanic cell the chemical cnergy change lo clectrical energy as a result of the spontaneous reaction. 1 9- Cathodic polarization is set when the potential is more positive than the Fans, and the cathodic current is less than the anodic current. ] [ ] 10- Redox reaction is a reaction in which there is a transfer of electrons from one species to another, Part II: multi-choice questions. 1- Identify the location of oxidation in an clectrochemical cell. A) The anode, B) The cathode, C) The electrode, D) The salt bridge 2- Determine the redox reaction represented by the following cell notation. Mg(s) | Mg2+(aq) || Cu2-(aq)Cu(s) A) Mg(s) + Cu2+(aq) + Cu(s) - Mg2+(aq) C) 2 Cu(s) + Mg2+(aq) > Mg(s) + 2 Cu2+(aq) B) 2 Mg(s) + Cu2+ aq) + Cu(s) + 2 Mg2+(aq) D) 3 Mg(s) - 2 Cu2-(aq) > 2 Cu(s) + 3 Mg2+(aq) 3- Which of the following would be the most (more) spontaneous reaction at 298 K? a) A +2B-C; Ecell= +0.98 V, b) A+B+2C; Eºcell =-0.030 V C) A+ B 3C; Bºcell - +0.15 V, d) A+B+C Bºcell +1.22 V 4-When the energy of Fcrmi level Ex>lumno energy for the reactant Othen, a) Electrons are transferred from clectrode to reactant. b) No electron transfer at all. c) Electrons are transferred from reactant to the electrode. d) Electrode at the equilibrium, 5- Which catalyst from the following you will use as an electrode for hydrogen production? a) Catalyst A, gives i = 10mA cm-at n = 30 mV. b) Catalyst B, gives i = 10-mAçm-at n = 30 mV. c) Catalyst C gives i = 10 % mA cm at n = 10 mV. d) Catalyst C. gives i = 10 mA cm-at n = 10 mV.
6- Which of the following reactions would have the smallest value of equilibrium constant (K) at 298 °K? a) A+B-C;E coll= +1.22 V, b) A + 2B-C: E cell = -0.98 V c) A+B 2C; Eºcell = -0.30 V. d) A+B 3C; Eºcell = -0.15 V 7- Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an clectrochemical cell at 25°C. (The oquation is balanced.) 3 Cl2(g) + 2 Fe(s) 6 Cl(aq) - 2 Fe3+(aq) Cl2(g) +20 2014 () Fc3+(aq) + 3 C + Fe(s) E° = -1.36 V E°= -0.04 V A) +4.16 V B)-1.40 V C) -1.32 V D) +1.32 V E) +1.40 V 8- Use the standard ball-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.) Sn(s) + 2 Ag+(aq) Sn2+(aq) - 2 Ag(s) Sn2-(aq) 12e → Sn(s) Ag (aq) → Ag(s) E = -0,14 V E° = -0,80 V A) +1.74 V. B) +0.94 V. C) +1.08 V, D) -1.08 V, E) - 1.74 V 9- What is the oxidizing agent in the redox reaction represented by the following cell molation! Sn(s) Sn2(aq) || Ag (aq) Ag(s) A) Sn(s) B) Ag (aq) C) Sn2 (aq) D) Ag(s) E) Pt 10- Usc thc tabulated half-cell potentials to calculate AG for the following balanced redox reaction. Pb2-ag) Cus) Pb(s) Cu2-(aq) A)-41 kJ B) -0,47 kJ C) +46 kJ D) +91 kJ E)-21 kJ Part III; definitions and derivations. 1- In Nernst Equation RT TO1 E=E+In R] Define the ETL and F parameters.
2- Sketch a diagram for llelmholtz Double Layer showing (a) inner llelmholtz plane, (b) outer llelmholtz plane (c) diffusion layer and (d) surface charge potential profile. (lect, 1-57). Then explain the main difference between Helmholtz and Gouy- Chapman diffusion Double Layer? 3- Sketch a diagrain for Tafel cquation showing the relation between Logi and n for (a) anodic reaction, (b) cathodic rcaction. Give the value for the slope at anodic reaction and value of the slop at cathodic reaction and the intercept with y-axis. 4- Starting with the AG = AGⓇ-RTINQ. Dcrive the Ncrtist Equation E = E-(0.059/11) logo Part IV: calculation. 1- Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in front of H2C204 and H20 in the balanced reaction? Mn04- (aq) 12C204(aq) → Mn2-(aq) + CO2(0) 2- Calculate Eceb and free energy (AG) at 25°C for the reaction: ing) 30u - 2M10 + 8H Mno Cu + 4H O (5) 1 (1) 213) tny) 2) 2+ Given Cu 1-0,010 M. [MnO 1 -2,0) M, LII ] - 10M. E"= 1.4 VT= 298 K and F=96485
3- Using the equation in K-F E cell RT calculate the value of K at 298 K for the following reaction? a) Cl2(g) + 2 c 2 C1- (aq) E° = -1.36 V b) Fe3(aq) + 3 → Feis) E = -0.04 V 4- The Butler-Volmer equation can be written as n = logio - (2.3 RT/anf)log i For a reaction at 298 K in which I = 1, a = 0.5, in = 2.0x10" A, calculate the current flowing al overpolcntials (m) of 30 IV and 150 mV using (a) the Butler-Volmer equation and (b) the Tafel equation. 5- Calculate the l. and I, from B-V equation assuming the following values: 1.-1x10' Acm',T-298K, --145 my 1.- Tx Açm-, T-298K, 1260 mV 1 = expl-anFn/RT) 1 =i expl(1-a)nF) n/RT] 6- The equilibrium potential for the reaction Ole = R is 0,5 V vs. SITE and k = 10 cm s?, A = 1,0 cm and transfer coefficient, a=0.5, if [0] = [R]= 1 mM what would the current density at 0.4V? 0 ((1-2)F71/RT) (-amin/RT) i = nfAK (Ce -Ce 1 red net OX 7- The data tabulated below was obtained for the couple CeCet al. : 0.5 chi Pt clectrode at 298 K. Assuming mass transfer cffects can be ignored determine the exchange CLTCI density and the transfer cocllicient for the reaction. potential mv 1η1A 150 78,2 175 112.5 200 225 250 275 150,3 178,8 212.7 288,9
8- The following data has been obtained for the "overvoltage” for the hydrogen electrode in a proton exchange membrane fuel cell, Current Density (OLA/cm) 40 43 47 SO 54 58 61 64 69 Overvoltage (IV) 72. 75.1 76,2 78.8 81,8 83.2 84,1 86.7 88,8 a) Construct an appropriate plot to prove the Talel equation can be used b) Use the given data to determine the values of slope and land a c) Use your values of a and i, to estimate the cell voltage at a current density of 125 mA/cm?