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### First Order Reactions

Posted: Tue Mar 12, 2019 11:21 pm
Can 2A -> B + C be a first order reaction and why?

### Re: First Order Reactions

Posted: Tue Mar 12, 2019 11:34 pm
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.

### Re: First Order Reactions

Posted: Wed Mar 13, 2019 2:06 pm
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.

### Re: First Order Reactions

Posted: Wed Mar 13, 2019 2:18 pm
reaction orders can only be determined experimentally, so it could be a first order but is not necessarily