For the reaction,
\(3 \mathrm{I}^{-(\mathrm{aq}, \mathrm{~s})}+\mathrm{S}_2 \mathrm{O}_{8(\mathrm{aq})}^{2-} \longrightarrow 2 \mathrm{SO}_{4(\mathrm{aq},)}^{2-}+\mathrm{I}_{3(\mathrm{aq},)}^{-}\)
rate of formation of \(\mathrm{SO}_{4(\mathrm{aq} .)}^{2-}\) is \(0.044 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{~s}^{-1}\).
Calculate rate of consumptiuon of \(\mathrm{I}_{(\mathrm{aq} .)}^{-}\).

\(3 \mathrm{I}_{\text {(aq) }}^{-}+\mathrm{S}_2 \mathrm{O}_{8(\mathrm{aq})}^{2-} \longrightarrow 2 \mathrm{SO}_{4(\text { aq })}^{2-}+\mathrm{I}_{3(\mathrm{aq})}^{-}\)
Rate of reaction
\(=-\frac{1}{3} \frac{\mathrm{~d}\left[\mathrm{I}^{-}\right]}{\mathrm{dt}}=-\frac{\mathrm{d}\left[\mathrm{~S}_2 \mathrm{O}_8^{2-}\right]}{\mathrm{dt}}=\frac{1 \mathrm{~d}\left[\mathrm{SO}_4^{2-}\right]}{2}=\frac{\mathrm{d}\left[\mathrm{I}_3^{+}\right]}{\mathrm{dt}}\)
\(\therefore \quad\) Rate of consumption of \(\mathrm{I}^{-}=-\frac{1}{3} \frac{\mathrm{~d}\left[\mathrm{I}^{-}\right]}{\mathrm{dt}}=\frac{1 \mathrm{~d}\left[\mathrm{SO}_4^2\right]}{2}\)
\(=\frac{3 \times 0.044}{2}=0.066 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{~s}^{-1}\)