I understand why changing the concentrations of the electrolytes in a voltaic cell affects the voltage. Given a zinc-copper cell for example, if I were to increase the concentration of the zinc sulphate electrolyte, the equilibrium between zinc ions and zinc metal would shift towards the side of the zinc metal. This would cause the reduction potential for zinc ions to increase, decreasing the overall cell potential. Please correct me if I’m wrong as this is how I understand it!

However, I don’t quite understand why temperature affects the voltage the way it does. According to the Nernst equation, if the reaction quotient is greater than one (meaning that the zinc sulphate concentration is greater than the copper sulphate concentration in this example), increasing temperature decreases voltage. Conversely, if the reaction quotient is less than one, increasing temperature increases voltage.

I am familiar with Le Chatlier's principle, but if I were to apply it to this scenario, given that the redox reaction taking place is exothermic, it would suggest that increasing temperature would always decrease the voltage produced since it would cause a shift towards the reactant side. This, of course, does not correspond with the relationship predicted by the Nernst equation.

I have looked all over the internet but I could not find any answer to this seemingly straightforward question. Any help is greatly appreciated!

  • 1
    $\begingroup$ Did you notice the temperature $T$ term in the Nernst equation? Try to derive the equation and what is the origin of $T$ there. Once you have done the mathematical derivation of the equation, one can think about temperature qualitatively. $\endgroup$
    – M. Farooq
    Feb 1 '20 at 23:07
  • 2
    $\begingroup$ Your mistake is assuming that the equilibrium constant K and the voltage are linearly related, so that a shift in K towards reactants will reduce voltage. The potential is a function of TlnK, so if T increases more than lnK decreases, the potential will actually increase. $\endgroup$
    – Andrew
    Feb 2 '20 at 2:16

Consider that even when exist a "driving force" to move ions to electrodes, it is necesary that particles stay not static, they need some capacity to move to change direction and take way to electrodes, and what gives this capacity to move, Energy, and in any particle system this energy distribution follows Maxwell-Bolzmann and this means that temperature counts.. e^-(1/kT)


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