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The last part of General Chemistry course in the Faculties of Engineering and Agricultural Sciences at my University is *electrochemistry* (covered by Chapter 8 of the Physical chemistry textbook).

I believe the Nernst equation (below) to be one of the most elegant results of thermodynamics, as well as a really powerful tool for a society which heavily relies on electricity – and, thus, desperately needs it, both for big factories and for personal mobile phones!

However, I usually find that students believe this equation to be difficult to *understand* (my main problem, instead, is to *pronounce* it, mainly because I’m Italian, and my native language uses far more vowels than the Nobel prize-winner Walther Nernst cares to use in his surname ).

Nernst equation contains every dream of scientists: work, equilibrium constants, logarithms, and **predictive ability**. Usually chemists prefer to use a *log _{10}* instead of a

The major issue comes from what it’s inside the logarithm; to correctly use it, one should use *activities* of the involved species. But activity is a difficult guest to handle (and *fugacity* doesn’t help simplifying the equation for gases, too!). For this reason, it is usual to use molar concentration for diluted species, and pressure for gases. It has to be noted that this works only if the values themselves are small enough to let us substitute the latter terms to the former ones.

Another problem usually arises when considering the difference between *halfcell* equation and *cell* equation. One can obtain electromotive force for a cell in two ways, either solving the *cell *equation or solving the two *halfcell* for any electrode and then subtracting the anode potential from the cathode potential.

A difficulty (and usual question) is the following: if I have to use the same number of electrons when balancing the *cell* reaction, why can I solve each *semireaction* by its own, and then merely subtract the values? Is not the number of electrons needed anymore?

The truth is: of course, the number of electron involved in each semireaction DOES count, but you already take it into account when calculating the equation… if you double the number of electrons, also exponents in the logarithm double, and so the global effect is null. For this reason, you can use both methods to calculate the emf in your cell (how nice!).

Lastly, the answer to the title question: Nernst equation is simple enough to be used, and so I deem the pronounciation more difficult. Right? Well, unless you have help 🙂

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