For the reaction

CHEMISTRY · Single correct · A Level · Chemistry · Rate equations · Rate equations

Problem

For the reaction

X + Y \rightarrow \text{products}

, initial-rate data were collected at 25 °C: Run 1: [X] = 0.10 M, [Y] = 0.10 M, initial rate =

2.0\times10^{-3}

M s

^{-1}

Run 2: [X] = 0.20 M, [Y] = 0.10 M, initial rate =

4.0\times10^{-3}

M s

^{-1}

Run 3: [X] = 0.20 M, [Y] = 0.30 M, initial rate =

1.2\times10^{-2}

M s

^{-1}

Which mechanism below is most consistent with these data? (a) Step 1 (slow):

X + X \rightarrow Z

Step 2 (fast):

Z + Y \rightarrow \text{products}

(b) Step 1 (slow):

X \rightarrow Z

Step 2 (fast):

Z + Y \rightarrow \text{products}

X + Y \rightarrow Z

Step 2 (fast):

Z \rightarrow \text{products}

(d) Step 1 (slow):

X + 2Y \rightarrow Z

Step 2 (fast):

Z \rightarrow \text{products}