Defining Cells Electromotive Force: The main objective of this particular aspect of Physical Chemistry is to examine the relation between free energies and the mechanical energy of electromotive force of electrochemical cells. The ionic components of aqueous solutions can be treated on the basis of the general methods which have been developed in electrochemical cells. But no means were developed there for the deduction of solute free energies from the direct relation between free energies and the mechanical energy can be obtained by harnessing a reaction involving these species.

Now arrangements are considered whereby the mechanical energy that can be obtained from a reversible chemical change can be determined. The procedure leads to a direct, and frequently very accurate, measurement of the free-energy change for the reaction. The arrangement consists of allowing, or forcing the reaction to proceed at a state of balance in an electrochemical cell. The electrical energy, which can be converted essentially completely too mechanical energy, is determined.

The reactions that occur in electrochemical cells generally involve the ionic species of parent electrolytes. Some of these are responsible for the passage of the electric current through the usually aqueous solution in the cell. Information on obtained from the results of electrical measurements.

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