Stoichiometric coefficients and order


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Lucia H 2L
Posts: 43
Joined: Mon Nov 14, 2016 3:00 am
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Stoichiometric coefficients and order

Postby Lucia H 2L » Thu Mar 08, 2018 7:05 pm

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
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am
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Re: Stoichiometric coefficients and order

Postby Ya Gao » Thu Mar 08, 2018 7:06 pm

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

Postby Shane Simon 2K » Thu Mar 08, 2018 9:21 pm

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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Joined: Sat Jul 22, 2017 3:01 am

Re: Stoichiometric coefficients and order

Postby Veronica Rasmusen 2B » Sat Mar 10, 2018 5:37 pm

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
Posts: 58
Joined: Fri Sep 29, 2017 7:06 am

Re: Stoichiometric coefficients and order

Postby Yeyang Zu 2J » Sun Mar 11, 2018 1:34 pm

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

Postby Wenxin Fan 1J » Wed Mar 14, 2018 7:03 pm

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.


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