Hydrogen iodide gas decomposes to hydrogen gas and iodine gas:
$$2 \mathrm{HI}(\mathrm{g}) \rightleftharpoons
\mathrm{H}_{2}(g)+\mathrm{I}_{2}(g)$$
To determine the equilibrium constant of the system, identical one-liter glass
bulbs are filled with \(3.20 \mathrm{~g}\) of \(\mathrm{HI}\) and maintained at a
certain temperature. Each bulb is periodically opened and analyzed for iodine
formation by titration with sodium thiosulfate, \(\mathrm{Na}_{2}
\mathrm{~S}_{2} \mathrm{O}_{3}\)
$$\mathrm{I}_{2}(\mathrm{aq})+2 \mathrm{~S}_{2} \mathrm{O}_{3}{ }^{2-}(a q)
\longrightarrow \mathrm{S}_{4} \mathrm{O}_{6}{ }^{2-}(a q)+2 \mathrm{I}^{-}(a
q)$$
It is determined that when equilibrium is reached, \(37.0 \mathrm{~mL}\) of
\(0.200 \mathrm{M}\) \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) is
required to titrate the iodine. What is \(K\) at the temperature of the
experiment?