Compare runs where only one concentration changes, calculate the rate factor and match it to concentration raised to power zero, one or two.
A group of students investigated the kinetics of a 'clock' reaction.
The reaction investigated was that between hydrogen peroxide and iodide ions in the presence of acid.
Reaction \(1 \quad \mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+2 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{I}^{-}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{I}_{2}(\mathrm{aq})\)
In this 'clock' reaction, a fixed volume of aqueous sodium thiosulfate, , and a small amount of starch were added to the reaction mixture.
The added thiosulfate ions react with the iodine produced in Reaction 1.
Reaction \(22 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-}(\mathrm{aq})+\mathrm{I}_{2}(\mathrm{aq}) \rightarrow \mathrm{S}_{4} \mathrm{O}_{6}^{2-}(\mathrm{aq})+2 \mathrm{I}^{-}(\mathrm{aq})\)
When all the thiosulfate ions have reacted, the presence of iodine is detected by the formation of a starch-iodine complex. The students recorded the time taken for this complex to form.
Four reaction mixtures, with different initial concentrations of hydrogen peroxide, hydrogen ions and iodide ions, were prepared.
Each mixture had the same volume and contained the same amount of sodium thiosulfate and starch.
Use the results in the table to deduce the order of Reaction 1 with respect to hydrogen peroxide, hydrogen ions and iodide ions. Justify each answer by referring to relevant data from the table.
Hydrogen peroxide
Hydrogen ions
lodide ions
