Evaluation of the Standard Cell Potential

We may usually with negligible error approximate the pressure factors of the solids and solutes by unity. The activities of the solids are then 1, the solute activities are a+ = 

By measuring Eceii, eq for a cell with known values of /mb and and with a derived value of gq, we can use this equation to find the mean ionic activity coefficient y of the HCl solute. This is how the experimental curve for aqueous HCl in Fig. 10.3 on page 296 was obtained. 

We can always multiply each of the stoichiometric coefficients of a reaction equation by the same positive constant without changing the meaning of the reaction. How does this affect the Nemst equation for the reaction equation above Snppose we decide to multiply the stoichiometric coefficients by one-half  

With this changed reaction equation, the value of z is changed from 2 to 1 and the Nemst equation becomes 

As we have seen, the value of the standard cell potential gg of a cell reaction has useful thermodynamic applications. The value of °gjj for a given cell reaction depends only on temperature. To evaluate it, we can extrapolate an appropriate function to infinite dilution where ionic activity coefficients are unity. 

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