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الموضوع: Cell Potentials

  1. #1
    عضو ذهبي الصورة الرمزية ماجده
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    افتراضي Cell Potentials

    Electrons from solution pushed onto the anode, around the external circuit and onto the cathode where they are pulled out into the solution.
    That's one way of thinking of the electrical circuit part of the electrochemical cell. The electrons pushed around the external circuit can do work (run a motor, illuminate a light bulb, etc). The amount of work possible is a function of both the voltage (potential) and of the current (number of electrons) in the circuit.
    Pushing one Coulomb of charge around a circuit at a potential of 1 Volt does One Joule of work. OR, mathematically, 1J = 1V × 1C.
    The cell potential (voltage of the cell) depends on the chemicals used. For example, the chemicals in dry-cells (batteries) are such that the potential is always about 1.5 V. This has become a standard and is now a limiting factor in deciding which chemicals can be used to create a battery.
    The cell potential is given a symbol of Ecell. If all chemicals are at activity of 1 (conc. = 1 M, p = 1 bar) then the cell potential is the standard cell potential and is given as E°cell.
    Any redox reaction has the potential (pun) to be used in an electrochemical cell. We merely need to be able to divide the oxidizing and reducing agents into two half cells (half reactions).
    Take for example, the reaction of zinc metal dissolving in hydrochloric acid. The reaction is:
    Zn(s) + 2H+(aq) ® Zn2+(aq) + H2(g)
    We need to separate the zinc from the hydrogen. We can use zinc as an electrode but what about the hydrogen.
    In this case, we need to set up a special electrode, which allows H2 gas molecules to interact directly with H+ dissolved in water and with the electrons from the external circuit simultaneously. Such a system is pictured below.
    A blow-up of the surface of the platinum electrode is shown below so the location of reaction can be better understood.
    The other half-cell would look much like that pictured in a previous diagram. The whole cell diagram, of course would include the external part of the circuit and the salt bridge or membrane to complete the circuit. We can abbreviate this diagram as follows:
    Zn(s)/ZnSO4(aq)//H2SO4(aq)/H2(g),Pt(s)
    [Anode // Cathode]
    Where the single slash mark / represents the boundary between solution and electrode and the double slash // represents the salt bridge or semi-permeable membrane. The external circuit, of course, joins the two electrodes (solid) and is not explicitly shown here.
    The overall cell voltage can be summed from the half-cell potentials of the oxidation and of the reduction reactions.
    Ecell = ERed + Eox.

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  2. #2
    عضو ذهبي الصورة الرمزية م.عبد الرحمن
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    افتراضي رد: Cell Potentials

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  3. #3
    عضو مميز الصورة الرمزية عماد الكردي
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    افتراضي رد: Cell Potentials

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  4. #4
    عضو مميز الصورة الرمزية قمر بلحاج
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    افتراضي رد: Cell Potentials

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