Question

Assuming an elementry reaction $H _{2} O _{2}+3I^{-}+2 H ^{+} \longrightarrow 2 H _{2} O + I _{3}^{-}$. 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 $[ I^- ]^{1}=2 I ^{-}$
$r _{2}= K \left[ H _{2} O _{2}\right]\left[2 I ^{-}\right]^{3}\left[ H ^{+}\right]^{2}$
$\Rightarrow 8 K \left[ H _{2} O _{2}\right]\left[ I ^{-}\right]^{3}\left[ H ^{+}\right]^{2}=8 r _{1}$