## Negative Orders

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

lauren chung 2f
Posts: 50
Joined: Fri Sep 29, 2017 7:03 am

### Negative Orders

On page 621 in the textbook, it discusses negative orders and gives examples of rate laws with the concentration of the products in the denominators. How do you know when you write the rate law with both the reactants and products?

Austin Ho 1E
Posts: 50
Joined: Fri Sep 29, 2017 7:04 am
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### Re: Negative Orders

Negative orders occur when you have to take the product into consideration for a rate law. For example, in the textbook's example: rate = k[O3]2[O2]-1, O2 is a product of the reaction. The reason why O2 is in the rate law is because its concentration is affecting the rate at which the reaction occurs.

In practice, you won't have to take the product into consideration in the rate law. This is because we typically take the rate law as rate=k[R], where [R] represents the reactants. This comes from taking the instantaneous rate at the start of the reaction, or the initial rate. We use this instead of trying to take [P] into account because it is much simpler to understand rates this way.