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Need Help Understanding Voltaic Cells

  1. Jul 2, 2010 #1
    Hi I just finished reading the chapter on electrochemistry from my chemistry text book (I just took the first half of general college chemistry this past semester) and I feel like I’m missing something- I don’t understand how electric fields play into the operation of the battery.

    I understand that in a battery, the transfer of electrons through the external pathway (wire), is a part of an oxidation reduction reaction which involves one substance in the anode half cell being oxidized(giving up electrons), and another substance being reduced(gaining electrons) in the cathode half cell.

    I also understand that a salt bridge or porous barrier is necessary in order for this process to occur because if the anions from the cathode were not allowed to migrate into the anode, then a net negative charge would build up in the cathode that would not allow additional electrons to flow in through the wire. This negative charge buildup in the cathode would eliminate the potential difference between the terminals. A similar net positive charge would develop in the anode if its cations couldn’t migrate into the cathode.

    It is my understanding that potential energy is defined by a conservative force and the configuration of the system of particles that it acts on. So if there is an electric potential difference between two terminals, shouldn’t there be an electric field between the terminals as well? And if there is an electric field in place between the two terminals, shouldn’t that mean that there is some sort of charge separation between the two terminals and that the cathode has a more net positive charge or the anode has a net negative charge? If this is the case, where is the charge separation? Don’t the solutions in the half cells need to remain electrically neutral for charge to flow?

    Assuming we have a simple battery with Cu and Zn electrodes, ZnSO4(aq) in the anode half cell and CuSO4(aq) in the cathode half cell, and a porous barrier separating the cells- can we say that the electric field produced by the positively charged Cu2+ ions in the cathode half cell produce such a strong electric field that they ionize the Zn, taking it’s valence electrons?

    Or do we say that because the Cu2+ ions form a solid when they come into contact with the free conducting electrons in the cathode electrode, that this process leaves the cathode with relatively few free conducting electrons and so by virtue of statistical probability or entropy or something the free conducting electrons in the wire drift in to fill the electron void, and as they drift into the electrode, the valence electrons of the Zn electrode drift off to fill the electron void in the wire and so on and so forth? If this is the case, where is the electric field which defines the difference in potential?

    Or Can we say that as the Cu2+ ions take the free conducting electrons from the cathode electrode, that this leaves the electrode with a net positive charge, and this net positive charge of the electrode creates the electric field which drives the current flow? If this is the case then why doesn’t this electric field created by the positively charged cathode electrode repel the incoming cations from the porous barrier?

    I’m sure the answer to all of this is obvious and I’m just an idiot, but if you could please humor me and spell it out I would really appreciate it. Thank you.
    Last edited: Jul 2, 2010
  2. jcsd
  3. Aug 14, 2010 #2
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