4
$\begingroup$

Consider the reaction $$\ce{2A + B -> Products}$$ When the concentration of $\ce{B}$ alone was doubled, the half-life did not change. When the concentration of $\ce{A}$ alone was doubled, the rate increased by two times. The units of the rate constant is:

a) $\mathrm{s^{-1}}$

b) $\mathrm{L\ mol^{-1}\ s^{-1}}$

c) Unitless

d) $\mathrm{mol\ L^{-1}\ s^{-1}}$

I have tried it solving through this method:

According to me, when the concentation of A alone was doubled, reaction rate also increased by two time, implies that Reaction is first order according to A. In same way, the reaction should be 0 order according to B. So net order would be 1. So this gives me answer $\mathrm{s^{-1}}$ but the answer is $\mathrm{L\ mol^{-1}\ s^{-1}}$. Where am I going wrong?

$\endgroup$
3
$\begingroup$

You are doing it wrong in situation when concentration of B alone was doubled but half life did not change.

In this situation, the reaction order should be 1 according to B as Half life in first order reaction doesn't depend upon initial concentration of reactants.

$t_{1/2} = \ln2 / K $

So the final order will be 2 and the answer of the question will be B.

Hope, this helped you. :)

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.