Verified Solution • 2025–26 Session moderate

QJEEM08Ch5142: JEE Main 2008 Chemistry - Class 12 JEEM08Ch5142 Solution: For a reaction rate of disappearance of ‘A’ is related to the…

For a reaction 12A→2B{1 \over 2}A \to 2B rate of disappearance of ‘A’ is related to the rate of appearance of ‘B’ by the expression

Multiple Choice Options

  • A −d[A]dt- {{d[A]} \over {dt}} = 12d[B]dt{1 \over 2}{{d[B]} \over {dt}}
  • B −d[A]dt- {{d[A]} \over {dt}} = 14d[B]dt{1 \over 4}{{d[B]} \over {dt}}
  • C −d[A]dt- {{d[A]} \over {dt}} = d[B]dt{{d[B]} \over {dt}}
  • D −d[A]dt- {{d[A]} \over {dt}} = 4d[B]dt4{{d[B]} \over {dt}}

Step-by-Step Verified Solution

The rates of reactions for the reaction

12A→2B{1 \over 2}A \to 2B

can be written either as

−2ddt[A]  - 2{d \over {dt}}\left[ A \right]\,\, with respect to ′A′'A'

or      \,\,\,\,\, 12ddt[B]    {1 \over 2}{d \over {dt}}\left[ B \right]\,\,\,\, with respect to ′B′'B'

From the above, we have

−2ddt[A]=12ddt[B]- 2{d \over {dt}}\left[ A \right] = {1 \over 2}{d \over {dt}}\left[ B \right]

or      \,\,\,\,\, −ddt[A]=14ddt[B]- {d \over {dt}}\left[ A \right] = {1 \over 4}{d \over {dt}}\left[ B \right]

i.e., correct answer is (b)

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