I was taught in class that a positive large half cell potential generally meant that the reaction was more favorable. What exactly does this mean? Doesn't a reaction with potential 4V need a greater input of energy to occur? Meaning that a lower electron cell potential would occur first and is therefore more favorable?

Also how why does Zn(II) +2e- ---> Zn favor the left side of the reaction? Shouldn't Zinc naturally tend towards being neutral?

  • $\begingroup$ And positive cell potentials suggest spontaneity right? $\endgroup$ – Idiot Mar 2 '17 at 19:06

That's not quite correct.

Half-reaction potentials are only really meaningful when you complete the redox pair, that is, you must have an oxidation and reduction reaction. The sum of the potentials is the potential for the full redox reaction at standard concentration and state. In that sense, the more positive either of the potentials is, the more favorable the overall reaction will be.

There is no preference for a neutral species in general. If you put sodium in water, the electron is quickly liberated and the end products of hydrogen and sodium ion are much more favored than the reactants of water and sodium.

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  • $\begingroup$ In a practice examination that I'm using to study for my upcoming midterm, one of the questions asks to choose three elements from a row of the periodic table and to give the order of the increasing oxidation half cell potential of the neutral element. Is it correct to assume that a more electronegative element would have the lowest half cell oxidation potential? Because it would be the most resistant to losing its electrons? $\endgroup$ – Idiot Mar 2 '17 at 19:14
  • $\begingroup$ That seems correct. You can also confirm this easily by consulting a table of reduction values. Your statement then becomes: electronegative elements should have more positive reduction potentials. $\endgroup$ – Zhe Mar 2 '17 at 20:51

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