Chapter 19, Problem 19.48QP

A mercury battery, used for hearing aids and electric watches, delivers a constant voltage (1.35 V) for long periods. The half-reactions are

$\begin{array}{l}\text{HgO}(s)+{\text{H}}_2\text{O}(l)+2{\text{e}}^{-}\stackrel{}{\to }\text{Hg}(l)+2{\text{OH}}^{-}(aq)\\ \text{Zn}(s)+2{\text{OH}}^{-}(aq)\stackrel{}{\to }\text{Zn}{(}_{\text{OH}}(s)+2{\text{e}}^{-}\end{array}$

Which half-reaction occurs at the anode and which occurs at the cathode? What is the overall cell reaction?