The spontaneous redox reaction in a voltaic cell has ____ (a) a negative value o
ID: 513880 • Letter: T
Question
The spontaneous redox reaction in a voltaic cell has ____ (a) a negative value of E_cell and a negative value of Delta G. (b) a positive value of E_cell and a positive value of Delta G. (c) a negative value of E_cell and a positive value of Delta G. (d) a positive value of E_cell and a negative value of Delta G. (e) a positive value of E_cell and a value zero for Delta G. An electronic device requires four 1.50-V AA alkaline batteries, which, connected in series, give 6.00 V. If the cell transfers two moles of electrons for each mole of reaction, what is the Gibbs free-energy change for the redox reaction in each of the batteries? (a) -1.45 times 10^2 kJ (b) +1.45 times 10^2 kJ (c) +5.79 times 10^2 kJ (d) -8.69 times 10^2 kJ (e) -2.90 times 10^2 kJ The magnitude of the charge on a mole of electrons is ____ (a) 1 C. (b) 9065 C. (c) 9.65 times 10^4 C. (d) 6.02 times 10^23 C. (e) 9650 C.Explanation / Answer
46. Any spontaneous reaction is given by the negative value of change in Gibbs free energy, i.e if during a reaction, Gibbs free energy is decreasing, that reaction would be a spontaneous reaction and would occur by itself without any conditions provided.
For a voltaic cell, the value of change in Gibbs free energy, dG is given by -nFE where n is the number of moles transferred in the redox process, F is the Charge on one mole of electron given by Faraday's constant = 96500 C/mol and E is EMF of the cell. Now since the expression already have negative sign with it, for a reaction to spontaneous E cell of that reaction should be positive.
Correct option is d.
47. Gibbs free energy change is given by -nFE ( terms are same as that in 46 ques).
dG = -nFE = -2 x 96500 x 6.00 Joules = -1158000 Jolues = -1158 KJ for 4 batteries.
For single battery, dG is -1158/4 = -289.5 KJ ~ -290 KJ.
Option e is correct.
48. Magnitude of charge on one mole of electron is given by 96500 C.
Charge on 1 electron is 1.6 x 10-19 C.
Number of electrons in one mole of electron = 6.022 x 1023.
Charge on one mole of electron = 1.6 x 10-19 C x 6.022 x 1023 = 96500 C/mol
Option c is correct.
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