Intermediate of rxn

[chiddler]

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In a multistep reaction, it is possible to measure an intermediate concentration to measure rate of reaction because its presence may indicate velocity of reaction.

In single step reactions, this is not possible because no intermediates exist.

👍?

 

[MedPR]

In a multistep reaction, it is possible to measure an intermediate concentration to measure rate of reaction because its presence may indicate velocity of reaction.

In single step reactions, this is not possible because no intermediates exist.

👍?

If the second step is the fast step in the multistep reaction, there may not be any intermediates because they will be consumed as they are made, similar to a single step reaction.

 

[chiddler]

If the second step is the fast step in the multistep reaction, there may not be any intermediates because they will be consumed as they are made, similar to a single step reaction.

Yes that is very true, but does this mean that you cannot monitor their concentration to find the corresponding rate of reaction?

My reasoning, and I feel better about this having slept on it, is that intermediate increases with increasing reagent concentration. You can find relative rate of reaction by determining how intermediate changes over time.

etc, pretty sure you know all this.

 

[MedPR]

Yes that is very true, but does this mean that you cannot monitor their concentration to find the corresponding rate of reaction?

My reasoning, and I feel better about this having slept on it, is that intermediate increases with increasing reagent concentration. You can find relative rate of reaction by determining how intermediate changes over time.

etc, pretty sure you know all this.

Yea if you're talking about using a marker or some kind of indicator that shows you when the intermediate is present, then sure. But it's unlikely that you will actually be able to quantitatively measure the amount of an intermediate. You can probably make a good guess based on changes in reactant/product as the reaction proceeds, but remember that even if you isolated a small sample of your reaction and were somehow able to measure the presence of intermediate, the reaction is still going on as you are measuring, and since intermediates are already in such small concentration, your measurements won't be very accurate.

Does that make sense?

 

[chiddler]

Yea if you're talking about using a marker or some kind of indicator that shows you when the intermediate is present, then sure. But it's unlikely that you will actually be able to quantitatively measure the amount of an intermediate. You can probably make a good guess based on changes in reactant/product as the reaction proceeds, but remember that even if you isolated a small sample of your reaction and were somehow able to measure the presence of intermediate, the reaction is still going on as you are measuring, and since intermediates are already in such small concentration, your measurements won't be very accurate.

Does that make sense?

If you're aliquoting part of reaction, then it only makes sense to stop the reaction as soon as it is aliquoted. You should see no intermediate in such cases.

I suppose this must only apply to spectating via UV spectroscopy. But yes, I understand what you're saying.

thanks very much for your help.