## First Order Reactions

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Fionna Shue 4L
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

### First Order Reactions

Can 2A -> B + C be a first order reaction and why?

armintaheri
Posts: 68
Joined: Fri Sep 28, 2018 12:26 am

### Re: First Order Reactions

I think the order of the reaction has to be determined experimentally. You can't just look at a reaction and tell what order it is. 2A -> B + C looks like a second-order reaction but it doesn't have to be one. What if the reaction took place in two steps and involved the intermediate molecules X and Y?

A -> X+Y Slow
X+Y+A -> B+C Fast

This would give us the rate law r=k[A], which makes the reaction first-order.

So any reaction could have any order. You can't tell what the order of the reaction is just by looking at it because you can't see all the intermediate steps.

Brian Chang 2H
Posts: 65
Joined: Fri Sep 28, 2018 12:17 am

### Re: First Order Reactions

Fionna Shue 4L wrote:Can 2A -> B + C be a first order reaction and why?

It CAN be first order, but doesn't necessarily have to be.

Reaction orders are determined experimentally and are not related to stoichiometric coefficients.

LaurenJuul_1B
Posts: 65
Joined: Fri Sep 28, 2018 12:17 am

### Re: First Order Reactions

reaction orders can only be determined experimentally, so it could be a first order but is not necessarily