Rate Law


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Madeline Ho 1C
Posts: 37
Joined: Mon Apr 23, 2018 3:00 am

Rate Law

Postby Madeline Ho 1C » Mon Mar 11, 2019 5:02 pm

Why is it that for elementary steps, the rate law can simply be found using molecularity but this does not apply to the overall balanced reaction?

2c_britneyly
Posts: 62
Joined: Fri Sep 28, 2018 12:16 am

Re: Rate Law

Postby 2c_britneyly » Mon Mar 11, 2019 5:49 pm

With elementary steps there's no ambiguity. If the equation is A+A--> B, then you know it requires two moles of A for B to form. If they only give you the overall reaction with no elementary steps, then there could be an intermediate you didn't know about.

Jayasuriya Senthilvelan 4I
Posts: 31
Joined: Thu Jan 10, 2019 12:17 am

Re: Rate Law

Postby Jayasuriya Senthilvelan 4I » Mon Mar 11, 2019 5:57 pm

With an overall reaction, we have no idea what steps go behind it. It could happen just as it is written, or there could be a number of elementary steps occurring in the background that are not obvious. For this reason, when we are given an overall reaction, we must examine its reaction mechanism (set of proposed elementary steps) in order to find the rate law. For each elementary step, we are assuming that it happens in a single step with no intermediate whatsoever.


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