In 1982, the International Union of Pure and Applied Chemistry (IUPAC) redefined the standard state pressure to

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In 1982, the International Union of Pure and Applied Chemistry (IUPAC) redefined the standard state pressure to be 1 bar. As a result, standard reduction potentials for half-cell reactions must be adjusted accordingly. In this problem, we illustrate the approach to adjusting these values. Since the hydrogen electrode reaction is assigned a value of 0 V, for both the old (1 atm) and new (1 bar) standards of pressure, the change in reduction potential for a half reaction should be calculated from the balanced equation that includes the following hydrogen electrode half-cell reaction.

1 2 H(g) H+ (aq) + e

For example, to calculate the change in reduction potential for the half-cell reaction NO3‾(aq) + 4 H+(aq) + 3 e‾ → NO(g) + 2 H2O(l), we focus on the overall equation obtained by combining these two half-reactions.

Oxidation: Reduction: Overall: NO3 (aq) + 4 H+ (aq) + 3 e 3 3{ H(g)  H+ (aq) + e-} IN NO(g) + 2 HO(1) H(g) +

Since the cell potential is directly proportional to the Gibbs energy of reaction, ΔrG = -zFEcell, the change in cell potential that results from a change in pressure (from 1 atm to 1 bar) is obtained by first calculating the corresponding change in the Gibbs energy of reaction.

(a) Starting from equation (13.34), show that A,G = AG* Avgas In (P/P*) where A,G and A,G* are the Gibbs

Eq. 13.34

G = [c  + dMB + ] Weighted sum of  values for products [ + b  + ] (13.34) Weighted sum of  values for

Eq. 19.14

A,G = - ZFE cell (19.14)

Eq. 19.15

A,G = -ZFEcell (19.15)

Table 19.1TABLE 19.1 Standard Reduction Potentials at 298.15 K and 1 atma Reduction Half-Cell Reaction Acidic solution

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General Chemistry Principles And Modern Applications

ISBN: 9780132931281

11th Edition

Authors: Ralph Petrucci, Jeffry Madura, F. Herring, Carey Bissonnette

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