The gas-phase decomposition of in the presence of a platinum surface obeys the…

CHEMISTRY · Subjective · AP · Chemistry · Kinetics · Kinetics

Problem

The gas-phase decomposition of

\text{NO}_2

in the presence of a platinum surface obeys the experimental rate law rate

= k[\text{NO}_2]^2[\text{Pt(s)}]

. Two mechanisms have been proposed: Mechanism 1 Step 1 (fast equilibrium)

\quad \text{Pt(s)} + \text{NO}_2 \;\rightleftharpoons\; \text{NO}_2\!\!-\!\!\text{Pt}

Step 2 (slow)

\quad \text{NO}_2\!\!-\!\!\text{Pt} + \text{NO}_2 \longrightarrow \text{NO} + \text{NO}_3\!\!-\!\!\text{Pt}

Step 3 (fast)

\quad \text{NO}_3\!\!-\!\!\text{Pt} \longrightarrow \text{NO} + \tfrac{1}{2}\text{O}_2 + \text{Pt(s)}

Mechanism 2 Step 1 (slow)

\quad 2\,\text{NO}_2 \longrightarrow \text{N}_2\text{O}_4

Step 2 (fast)

\quad \text{N}_2\text{O}_4 + \text{Pt(s)} \longrightarrow \text{NO} + \text{NO}_3\!\!-\!\!\text{Pt}

Step 3 (fast)

\quad \text{NO}_3\!\!-\!\!\text{Pt} \longrightarrow \text{NO} + \tfrac{1}{2}\text{O}_2 + \text{Pt(s)}

Which mechanism (1 or 2) is consistent with the rate law? State the mechanism number and give one-sentence reasoning.