Confusion about intermediates

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Confusion about intermediates

Postby dchenny206 » Sun Feb 12, 2017 10:18 pm

On page 69 of the course reader, a proposed reaction mechanism is outlined in two steps:

STEP 1: NO2(g) + NO2(g) --> NO3(g) + NO(g)

STEP 2: NO3(g) + CO(g) --> NO2(g) + CO2(g)

OVERALL RXN: NO2(g) + CO(g) --> NO(g) + CO2(g)

Before that, it says that the proposed intermediate species is NO3. Is this because in step 1, it was formed as a product and in step 2, it was used immediately as a reactant?
Also, I don't quite understand why it is important to identify the intermediate. What useful information does this tell us about the kinetics of a reaction?

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Re: Confusion about intermediates

Postby Chem_Mod » Sun Feb 12, 2017 11:39 pm

Yes. an intermediate of a reaction is one that is formed in the midst of the reaction, but we do not see in the final products, it is merely a transitory element.
This is important because most reactions of molecules do not go straight from reactants to products, they undergo a stepwise fashion. Also, the rate of the reaction often depends on the rate limiting step. More often than not, that rate limiting step involves the formation of an unstable intermediate that requires a lot of energy to form, in order for the subsequent steps to happen. So yes, intermediates are very important.

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Re: Confusion about intermediates

Postby 404757006 » Fri Feb 17, 2017 3:02 pm

So are intermediates anything that is going to be canceled from side to side?

Miya McLaughlin 2B
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Re: Confusion about intermediates

Postby Miya McLaughlin 2B » Fri Feb 17, 2017 4:14 pm

Yes. When you add the equations together, all the intermediates should cancel out. Intermediates won't be in the final equation that represents the overall reaction.

Jordan Pace 2B
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Re: Confusion about intermediates

Postby Jordan Pace 2B » Fri Feb 17, 2017 4:20 pm

As stated above, most chemical reactions are stepwise. For clarity, a stepwise reaction is a chemical reaction with one or more reaction intermediates and involves at least two consecutive elementary reactions. An intermediate is formed from the reactants or preceding intermediates and reacts to produce the products of a chemical reaction. An intermediate helps a reaction occur, but does not show up in the final product because intermediates are used up during the reaction.

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