## Stoichiometric coefficients and order

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

Lucia H 2L
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### Stoichiometric coefficients and order

I know that stoichiometric coefficients are only supposed to influence rate in the unique rate laws for each substance.
But don't moles also affect rate? i.e. if you have
NO + NO --> N2O2
Wouldn't the rate be k[NO][NO] aka k[NO]^2, aka second order?

In general, how can you tell which rate law to use just by looking at the equation ?

Ya Gao
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### Re: Stoichiometric coefficients and order

You cannot determine the rate law by justing looking at the balanced equation unless it is an elementary step.

Shane Simon 2K
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Joined: Fri Sep 29, 2017 7:05 am

### Re: Stoichiometric coefficients and order

As a general rule, I would just not use the stoichiometric coefficients to find the order of a reaction. They line up sometimes but a lot of the times they do not. In many questions where you have to use rate laws, the order will either be given or you can find it without using the coefficients. If it is elementary, then you can use the coefficients but in other cases you cannot.

Veronica Rasmusen 2B
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### Re: Stoichiometric coefficients and order

For the most part, you should not use the balanced reaction and stoichiometric coefficients to find the order of a reaction. The order of the reaction will most likely be given in a question, or you will be given experimental data or a graph which you can use as well.

Yeyang Zu 2J
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Joined: Fri Sep 29, 2017 7:06 am

### Re: Stoichiometric coefficients and order

You can tell the reaction rate equation by simply looking at its chemical equation.
Rate equation is determined by experiment.
Only it works if the chemical reaction is a mechanical step of the reaction.

Wenxin Fan 1J
Posts: 53
Joined: Thu Jul 13, 2017 3:00 am

### Re: Stoichiometric coefficients and order

The coefficients are helpful when using elementary steps to try to determine the reaction mechanism, but the actual rate law can only be determined through experimentation.