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$$aA+bB \rightarrow cC + dD$$ The reaction rate is defined as: \begin{align} Rate = (\frac{1}{a})(\frac{-\Delta[A]}{\Delta t}) = (\frac{1}{b})(\frac{-\Delta[B]}{\Delta t}) = (\frac{1}{c}) (\frac{\Delta[C]}{\Delta t}) = (\frac{1}{d})(\frac{\Delta[D]}{\Delta t}) \\ \end{align} Is there a point of defining the reaction rate as the rate of disappearance of a reactant over its coefficent, or the rate of appearance of a product over its coefficent? Why not just saying the rate of disappearance of a reactant or the rate of appearance of a product?

Muhammad
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    Because then, as your equations show, we would have 4 different rates for a reaction like this. Its much simpler to divide each by the coefficients so that there is one common rate of reaction. – Tyberius Jan 09 '18 at 19:01
  • The question was just marked as a duplicate because it has been answered elsewhere on the site – Tyberius Jan 11 '18 at 05:08

1 Answers1

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There is no defining.

When you write down the multiplication table, you don't define that $2\times4=8$, as if it could have been anything else. Instead, you derive it according to the common rules. Same thing here.

The rate of anything is just how many times a second something happens. If we are interested in the rate of reaction, then our "something" stands for the reaction, just as written in the equation above, i.e., the act of consuming $a$ moles of $A$, $b$ moles of $B$, etc.

So it goes.

Ivan Neretin
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