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Reversible and Irreversible Cells
A cell is said to be reversible if the following two conditions are fulfilled
(i) The chemical reaction of the cell stops when an exactly equal external emf is applied.
(ii) The chemical reaction of the cell is reversed and the current flows in opposite direction when the external emf is slightly higher than that of the cell. Any other cell, which does not obey the above two conditions, is termed as irreversible. Daniell cell is reversible but cell is irreversible in nature
(5) Types of electrochemical cells: Two main types of electrochemical cells have been reported, these are,
(i) Chemical cells: The cells in which electrical energy is produced from the energy change accompanying a chemical reaction or a physical process are known as chemical cells. Chemical cells are of two types,
(a) Chemical cells without transference: In this type of chemical cells, the liquid junction potential is neglected or the transference number is not taken into consideration. In these cells, one electrode is reversible to cations while the other is reversible to the anions of the electrolyte.
(b) Chemical cells with transference: In this type of chemical cells, the liquid-liquid junction potential or diffusion potential is developed across the boundary between the two solutions. This potential develops due to the difference in mobilities of and ions of the electrolytes.