A battery is made from electrochemical cells. Referencing the Nernst equation, e
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Question
A battery is made from electrochemical cells. Referencing the Nernst equation, explain why a battery dies. 2. The Vernier pH sensor functions by measuring a voltage between two electrochemical cells and converts that to a pH value. One half of the electrochemical cell is the solution that is being tested, and the other half is a Ag-AgCl cell within the sensor. With this information, explain why the pH measurement of deionized water may not make sense. 3. Activity is often more appropriate to use when making electrochemical measurements than concentration. Activity is the "effective concentration" of a species or ion relative to a standard (1 M) and accounts for non-ideal behavior of a solution. How does the notion of activity influence your conclusion in Part C? How could we account for this in our experiment? 4. You likely observed bubbles when you placed Mg metal in the Mg^2 solution. Explain the formation of the bubbles and write the two half reactions involved.Explanation / Answer
1) Chemical elements contain intrinsic electrochemical energy potential associated with the energy of the electrons in the outermost electron shell or valence band in the atom and whether in its current state it has a potential surplus or deficit of electrons. These outermost electrons, called the valence electrons, determine how the atom reacts chemically with other atoms. Atoms in which the valence shell is full tend to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive because the extra electrons are easily removed to form positive ions (oxidation). Atoms with one or two valence electrons less than a closed shell are also highly reactive because of a tendency either to gain the missing electrons and form negative ions (reduction), or to share electrons and form covalent bonds. The lowest energy for a species is when its outer shell is fully occupied by electrons. The gaining or losing of electrons changes the energy level of the atom and it is this energy which is released as electrical energy during the discharge of a primary or secondary battery, or is absorbed when charging a secondary battery.
The energy available in an atom to do external work is called the Gibbs Free Energy and an indication of the magnitude of this potential energy realease is given by the electrode potential of the element. For a balanced reaction, this is expressed in the following equation:
G = - E0 n. F
Where
G is The change in Gibbs Free Energy in Joules
E0 is the standard electrode potential or EMF in Volts (See table above)
n is the number of moles of electrons transferred in the cell reaction per mole of reaction
F is the Faraday constant in Coulombs per mole (the magnitude of electric charge per mole of electrons)
This equation is used to calculate the energy available from the redox reactions possible with various combinations of active chemicals.
The voltage or potential difference between an oxidation and reduction reactions arises from the different electrochemical potentials of the reduction and oxidation reactions in the battery. The electrochemical potential is a measure of the difference between the average energy of the outer most electrons of the molecule or element in its two valence states.
the repeated and constant chemical reactions inside the battery leave dissolved metal on the cathode and, to a lesser extent, the anode. This can eventually form a sort of unwanted metallic plating on both.
Additionally, electrolytes in the battery are prone to decomposing. They oxidize on the cathode, leaving something like rust blocking the way of ions that are trying to jump back and forth. Common shorthand for this phenomenon is corrosion, and its effects are profound: The resulting battery, with its tired electrodes, broken-down electrolytes and corroded surfaces, is the picture of aging. It's now terrible at being a battery.
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