Pre-Equilibrium Approximation Practice Test

A reaction is proposed to proceed by the following mechanism. The first step is fast and reversible and is described as establishing a pre-equilibrium prior to the slow step.

Step 1 (fast, reversible; pre-equilibrium): $\mathrm{Br_2 + Fe^{2+} \rightleftharpoons FeBr_2^{2+}}$

Step 2 (slow): $\mathrm{FeBr_2^{2+} + Fe^{2+} \rightarrow 2Fe^{3+} + 2Br^-}$

Under these pre-equilibrium conditions, which qualitative rate law is most consistent with the mechanism?

A mechanism is proposed in which an early step is fast and reversible and is stated to establish a pre-equilibrium before the slow step.

Step 1 (fast, reversible; pre-equilibrium): $\mathrm{Fe^{3+} + SCN^- \rightleftharpoons FeSCN^{2+}}$

Step 2 (slow): $\mathrm{FeSCN^{2+} + H_2O \rightarrow Fe^{2+} + HSCN + OH^-}$

Which qualitative rate law is most consistent with the mechanism under pre-equilibrium conditions?