A student says, "The initial concentration of a reactant was doubled, and the rate doubled. Therefore the reaction is second order in that reactant." Why might the student say that? What is wrong with the statement? What is the actual order with respect to the reactant?

Answer is in the explanation.

Explanation:

The statement:  "The initial concentration of a reactant was doubled, and the rate doubled" implies the initial concentration is directly proportional to rate of reaction. That is:

Rate = K [A]₀

But this law is rate law of first order reaction. Second order reaction has as law:

Rate = K [A]₀²

These law implies:  "The initial concentration of a reactant was doubled, and the rate quadruplicate", a different statement.

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