Electrochemical cell and Gibbs Energy of the Reaction

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chemistry 12th class cbse notes

Electrochemical cell and Gibbs Energy of the Reaction

Electrical work done in one second is equal to electrical potential multiplied by total charge passed. If we want to obtain maximum work from a galvanic cell then charge has to be passed reversibly. The reversible work done by a galvanic cell is equal to decrease in its Gibbs energy and therefore if the emf of the cell is E and nF is the amount of charge passed and ΔrG is the Gibbs energy of the reaction, then

Electrochemical cell and Gibbs Energy of the Reaction
It may be remembered that E(cell) is an intensive parameter but ΔrG is an extensive thermodynamic property and the value depends on n. Thus, if we write the reaction

Electrochemical cell and Gibbs Energy of the Reaction

But when we write the reaction

Electrochemical cell and Gibbs Energy of the Reaction

Electrochemical cell and Gibbs Energy of the Reaction

If the concentration of all the reacting species is unity, then E(cell)

Electrochemical cell and Gibbs Energy of the Reaction

Thus, from the measurement of ECell we can obtain an important thermodynamic quantity, ΔrG, standard Gibbs energy of the reaction.
From the latter we can calculate equilibrium constant by the equation:

Electrochemical cell and Gibbs Energy of the Reaction

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