0
$\begingroup$

Can the Nernst equation always be applied to the overall redox reaction as opposed to only half cell reactions?

For example, in the following silver-silver chloride electrode: $$\ce{Ag (s)|AgCl (s)|Cl- (aq)}$$ rather than applying the Nernst eqution to the half cell reaction $$\ce{AgCl + e- -> Ag + Cl-}$$ can I apply it to $$\ce{AgCl -> Ag+ + Cl-}$$

The answer is the same for the question I was trying to solve (whether I use the overall reaction or the half-cell reaction), but I was wondering if this was just a coincidence or if it was the same.

If they are the same, are there any other factors I should consider such as whether or not the electrolyte fully dissociates in the given conditions?

$\endgroup$
  • $\begingroup$ $$\ce{AgCl -> Ag+ + Cl-}$$ is not a redox equation! $\endgroup$ – Yomen Atassi Jun 13 '16 at 14:33
1
$\begingroup$

It is coincidence, since $$\ce{AgCl -> Ag+ + Cl-}$$ is not a half cell reaction.

The silver chloride electrode functions as a redox electrode and the reaction is between the silver metal (Ag) and its salt — silver chloride (AgCl). There are two ways to represent the processes (half reactions) happening on the electrode: $$\ce{AgCl + e- -> Ag + Cl-}$$ or $$\ce{Ag+ + e- -> Ag}$$ $$\ce{AgCl -> Ag+ + Cl-}$$

And you should be applying Nernst equation to one of the two half cell reactions shown above.

The reason why you got the same result/answer is because the Nernst equation for silver chloride electrode has the dependence on the activity or effective concentration of only chloride-ions.

$$E = E^0 - \frac{\mathrm RT}{\mathrm F}\ln(a(\ce{Cl^-}))$$

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.