No values were given, but it is assumed R= 8.314 J/mol*K, F= 96485J/ V*mol, T= 2

Question

No values were given, but it is assumed R= 8.314 J/mol*K, F= 96485J/ V*mol, T= 298K, n= number of electrons

and the equations

Br2(aq) + 2e- ---> +1.0873 E= +1.0873v

I2(s) + 2e- ----> 2I- E= 0.5355v

Cr^3+ (aq) + 3e- ----> Cr(s) E= -0.744v

Cu^2+ (aq) + 2e- ----> Cu(s) E= +0.337v

What is the value of the equilibrium constant for the reaction between each pair at 25 degree C? (a) Cr(s) and Cu^2+(aq) 2.88e+109 (b) I_2(s) and Br^- (aq) E^degree_cell = RT/nF ln K E_degree_cell = E^degree_reduction - E^degree_oxidation

Explanation / Answer

(b) Reduction half reaction

I2(s) + 2e- ----> 2I-

oxidation half reaction

2Br- ---> Br2(aq) + 2e-

Ecell = Ereduction - Eoxidation = 0.5355 - 1.0873 = -0.5518 V

Ecell = RT/nF lnK

lnK = 2 * 96487 * (-0.5518) / 8.314 * 298 = -42.979

K = 2.16 * 10-19

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