[Mr. Raru]

If the net reaction A+B yields C proceeds by a single-step bimolecular mechanism, is it true that this must be a second order equation since it proceeds in only a single-step mechanism?

The Question taken out of the next was:
For the net reaction A+B yields C, which proceeds by a single-step bimolecular mechanism, which one of the following equations hold true?

a) t_1/2 = 0.693/k
b) Rate of reaction = k[A]
c) Rate of appearence of C = rate of disappearence of A
d) ln [A] = -kt +ln[A]₀

My guess is that a and d are both incorrect, because the reaction is at least a second order reaction. The answer in my book says c, but why would b be incorrect? Additionally is there a difference between rate of appearence and rate of formation. In a similar question, the rate of formation of a product was said to equal the negative rate of disappearence of the reactant. In order to make since, wouldn't answer c have to be worded rate of appearence of C = -rate of disappearenc of A?

If anybody can help, thank you

[Mr. Raru]

Since the reaction mechanism is a single step, wouldn't the net reaction therefore also be the elementery reaction? And if this is so, couldn't i use the coefficients on the molarity to decide the order? Since the coefficients are all one, the order of A is 1 and B is 1 so the reaction has to be second order, right? Can anyone help and tell me where I am incorrect?

[madscientist]

If the net reaction A+B yields C proceeds by a single-step bimolecular mechanism, is it true that this must be a second order equation since it proceeds in only a single-step mechanism?

The Question taken out of the next was:
For the net reaction A+B yields C, which proceeds by a single-step bimolecular mechanism, which one of the following equations hold true?

a) t_1/2 = 0.693/k
b) Rate of reaction = k[A]
c) Rate of appearence of C = rate of disappearence of A
d) ln [A] = -kt +ln[A]₀

My guess is that a and d are both incorrect,

Your spot on, a and d are incorrect, I would say that  b is the only true equation.

cheers

madscientist :albert:

[madscientist]

Not sure bout c

[veljanovski]

I think also that (b) is the right answer.

It is a law for every single-step bimolecular reaction. There is a case when this law is not important. And that is only when A is in excess than the reaction is pseudo first order and the laws are for reactions from first order.

C is also incorrect. “Rate of appearence of C = rate of disappearence of A „ is only in:

A -> C

A->B->C

This tip of reactions.