Question

Assuming an elementry reaction $H_2{O}_2+3I^{-}+2H^{+}⟶2H_{2}O+I_3^{-}$. The effect on the rate of this reaction brought about by doubling the concentration of $I^{-}$without changing the order

• A. The rate would increase by a factor of 3
• B. The rate would increase by a factor of 8
• C. The rate would decrease by a factor of $1/3$
• D. The rate would increase by a factor of 9

Answer 1

Answer: (B)

$r=K\left[H_2{O}_2\right]{\left[I^{-}\right]}^3{\left[H^{+}\right]}^2$
given $[I^{-}{]}^1=2I^{-}$
$r_2=K\left[H_2{O}_2\right]{\left[2I^{-}\right]}^3{\left[H^{+}\right]}^2$
$\Rightarrow 8K\left[H_2{O}_2\right]{\left[I^{-}\right]}^3{\left[H^{+}\right]}^2=8r_1$