Question

A hypothetical reaction X2 + Y2$\longrightarrow$ 2XY follows the mechanism given below.

X2 X + X $\rightleftharpoons$ [Fast]

X + Y2$\longrightarrow$ XY + Y [Slow]

X + Y $\longrightarrow$XY [Fast]

The order of overall reaction is

• A. 2
• B. 1
• C. 1.5
• D. Zero

Answer 1

Answer: (C)

1.5

Answer 2

$\text{Rate = K }\lbrack X\rbrack\lbrack Y_{2}\rbrack$

$K_{eq} = \frac{\lbrack X\rbrack^{2}}{\left\lbrack X_{2} \right\rbrack}$

$\lbrack X\rbrack = \sqrt{K_{eq}} \times \left\lbrack X_{2} \right\rbrack^{1/2}$

Rate = $K \times \ \sqrt{K_{\text{eq}}}\lbrack X_{2}\rbrack_{\text{1/2}}\ \lbrack Y_{2}\rbrack$

So the order of overall reaction is 1.5

$K_{eq} = \frac{\lbrack X\rbrack^{2}}{\left\lbrack X2_{a} \right\rbrack}$

$\lbrack X\rbrack\text{ =}\sqrt{K_{\text{eq}}}\lbrack X_{2}\rbrack^{\text{1/2}}$