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117. What are fuel cells? Write the reaction of a oxygen hydrogen fuel cell.

Fuel cell: A galvanic cell in which the reactants are continuously fed into the cell and the products are continuously removed is called a fuel cell.
The most important fuel cell is hydrogen oxygen fuel cell.
The reactions taking place in this fuel cell are
At cathode:
$straight O subscript 2 plus 2 straight H subscript 2 straight O left parenthesis straight l right parenthesis plus 4 straight e to the power of minus rightwards arrow 4 OH to the power of minus space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space straight E to the power of 0 subscript cathode space equals space 1.229 space straight V$
At anode:
$2 straight H subscript 2 left parenthesis straight g right parenthesis plus 4 OH to the power of minus space rightwards arrow space 4 straight H subscript 2 straight O plus 4 straight e to the power of minus space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space straight E to the power of 0 subscript cathode space equals space 0.00 space straight V$
Net reaction:

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118.

What is a mercury cell? Give the electrode reactions?

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119. What is the effect of change in (a) concentration, (b) temperature on the electrode potential of a given half-cell?

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120. Iron does not rust even if the zinc coating is broken in a galvanised iron pipe but, rusting occurs much faster if the tin coating over iron is broken. Explain?

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