For the reaction $aA + bB \to cC + dD$, the rate in terms of stoichiometric coefficients is:
A$-\dfrac{1}{a}\dfrac{d[A]}{dt} = -\dfrac{1}{b}\dfrac{d[B]}{dt} = \dfrac{1}{c}\dfrac{d[C]}{dt} = \dfrac{1}{d}\dfrac{d[D]}{dt}$
B$-\dfrac{d[A]}{dt} = \dfrac{d[B]}{dt}$ only
C$-a\dfrac{d[A]}{dt} = -b\dfrac{d[B]}{dt} = c\dfrac{d[C]}{dt} = d\dfrac{d[D]}{dt}$
D$\dfrac{d[A]}{dt} = \dfrac{d[B]}{dt} = \dfrac{d[C]}{dt} = \dfrac{d[D]}{dt}$
Answer & Solution
Correct answer: A. $-\dfrac{1}{a}\dfrac{d[A]}{dt} = -\dfrac{1}{b}\dfrac{d[B]}{dt} = \dfrac{1}{c}\dfrac{d[C]}{dt} = \dfrac{1}{d}\dfrac{d[D]}{dt}$
Each species rate is divided by its stoichiometric coefficient so that one rate of reaction can be defined consistently.
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