Use Fig. 5.1 to determine the initial rate of reaction 1. Show your working.
The rate equation for reaction 1 is rate $= k[\text{S}_2\text{O}_8^{2-}][\text{I}^-]$. Suggest why a large excess of iodide ions makes it possible to determine the rate constant from the half-life in this investigation.
Persulfate ions, $\text{S}_2\text{O}_8^{2-}$, react with iodide ions in reaction 1, and the process is catalysed by $\text{Fe}^{2+}$ ions. Write two equations to show how $\text{Fe}^{2+}$ catalyses reaction 1.
Describe the effect of an increase in temperature on the rate constant and the rate of reaction 1.
In aqueous solution, thiosulfate ions, $\text{S}_2\text{O}_3^{2-}$, react with hydrogen ions, as shown in reaction 2, $\text{S}_2\text{O}_3^{2-} + 2\text{H}^+ \rightarrow \text{SO}_2 + \text{S} + \text{H}_2\text{O}$. Under certain conditions, the reaction is first order with respect to $[\text{S}_2\text{O}_3^{2-}]$ and zero order with respect to $[\text{H}^+]$. The rate constant, $k$, for this reaction is $1.58 \times 10^{-2}\,\text{s}^{-1}$. Calculate the half-life, $t_{1/2}$, for reaction 2.
Nitrosyl bromide, $\text{NOBr}$, can be produced as shown in reaction 3, $2\text{NO}(g) + \text{Br}_2(g) \rightarrow 2\text{NOBr}(g)$. The rate is first order with respect to $[\text{NO}]$ and first order with respect to $[\text{Br}_2]$. The mechanism has two steps. Suggest equations for the two steps of this mechanism. State which is the rate-determining step.