Electrochemical Cell Electrochemical Cell An electrochemical cell is a device capable of either deriving electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy. A common example of an electrochemical cell is a standard 1.5-volt "battery". (Actually a single "Galvanic cell"; a battery properly consists of multiple cells, connected in either parallel or series pattern.) Equilibrium reaction Each half-cell has a characteristic voltage. Different choices of substances for each half-cell give different potential differences. Each reaction is undergoing an equilibrium reaction between different oxidation states of the ions: when equilibrium is reached, the cell cannot provide further voltage. In the half-cell which is undergoing oxidation, the closer the equilibrium lies to the ion/atom with the more positive oxidation state the more potential this reaction will provide. Similarly, in the reduction reaction, the further the equilibrium lies to the ion/atom with the more negative oxidation state the higher the potential.
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Working of Electrochemical Cell When the circuit is completed, a deflection is observed in the (G) towards the zinc electrode indicating that the e- are flowing from the Zn electrode to Cu electrode. At the Zn electrode, oxidation takes place. The electron 'e' is removed, lost or retained by the metal move through the material contained in the electrode and reach the Copper electrode at which they are accepted by Copper ions of the solution to form the neutral Copper atoms. In an electrochemical cell, each electrode constitutes one half of the cell and the reaction taking place at the electrode is called half-cell reaction. The overall cell reaction is obtained by adding the two half-cell reactions (1) and (2). From this, it is found that, when Zn is added to CuSO4 solution, Zn displaces Cu from CuSO4 with the liberation of heat. But, in the electrochemical cell, there is no direct contact between Zn and CuSO4. The heat energy that would have been liberated, appears in the form of electrical energy. Hence, the electrochemical cell acts as a source of current although for a short interval. Electrochemical Cell Equation In general, the electrode at which reduction takes place is written on the RHS of the salt bridge and the electrode at which oxidation takes place is written on the LHS of the salt bridge. The salt bridge linking the aqueous solutions is represented by two vertical parallel lines having ions on both sides.
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Solved Example Question: Depict the Galvanic cell in which the following reaction takes place Zn(s) + 2Ag+(aq) → Zn2+(aq) + 2Ag(s) Also show individual reactions at each electrode. Solution: The cell notation is Zn(s) | Zn2+(aq) || Ag+(aq) | Ag(s) Reaction at Anode: Zn(s) → Zn2+(aq) + 2eReaction at cathode: 2Ag+(aq) + 2e- → 2Ag(s)
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