Question

With chemical reactions, explain why the dry cell is a primary battery.

Answer 1

The overall reaction occurring in the dry cell produces 1.5 volts:            

anode:-    Zn(s) = Zn2+(aq) + 2e–  

cathode:-  2 e– + 2 NH4+(aq) = 2 NH3(g) + H2(g)  

       2 NH3(g) +        Zn+2 (aq) =                                  [Zn(NH3)2]2+(aq)    

H2(g) + 2 MnO2(s)  Mn2O3(s) + H2O(l)

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Zn(s) + 2 NH4+(aq) + 2 MnO2(s)     =  [Zn(NH3)2]2+(aq) + Mn2O3(s) + H2O(l)

A primary cell is a battery (a Galvanic cell) that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell (rechargeable battery). In general, the electrochemical reaction occurring in the cell is not reversible, rendering the cell unrechargeable.