(a) Show that the three elementary steps add up to give the...

Name: Problem 51, Chapter 15: Chemistry and Chemical Reactivity
Uploaded: 2020-07-14T22:26:03-08:00
Duration: 3 min 42 s
Channel: Anatole Borisov
Description: (a) Show that the three elementary steps add up to give the overall, stoichiometric equation. (b) What is the molecularity of each step? (c) For this mechanism to be consistent with kinetic data, what must be the experimental rate equation? (d) Identify any intermediates in the elementary steps in this reaction.

(a) Show that the three elementary steps add up to give the overall, stoichiometric equation. (b) What is the molecularity of each step? (c) For this mechanism to be consistent with kinetic data, what must be the experimental rate equation? (d) Identify any intermediates in the elementary steps in this reaction.

(a) Show that the three elementary steps add up to give the overall, stoichiometric equation.
(b) What is the molecularity of each step?
(c) For this mechanism to be consistent with kinetic data, what must be the experimental rate equation?
(d) Identify any intermediates in the elementary steps in this reaction.

Key Concepts

Reaction Intermediate

A reaction intermediate is a species that is formed in one elementary step and consumed in a subsequent step, and therefore does not appear in the overall balanced equation. Intermediates are transient in nature and often have very short lifetimes within the reaction sequence.

Elementary Step

An elementary step is a single-stage process in a reaction mechanism where reactants transform directly into products. It reflects a simple collision or rearrangement event and is written with a formula that directly indicates the number and type of molecules involved in that specific event.

Overall Stoichiometric Equation

The overall stoichiometric equation represents the net transformation of reactants to products, obtained by algebraically summing the individual elementary steps. This process involves canceling any intermediates that appear on both sides, resulting in a balanced equation that reflects the macroscopic reaction.

Molecularity

Molecularity refers to the number of reactant molecules involved in an elementary step. It characterizes the elementary process as unimolecular, bimolecular, or termolecular. This concept is critical because it directly influences the reaction’s rate law as deduced from the mechanism.

Rate Equation

The rate equation (or rate law) expresses how the rate of a reaction depends on the concentration of its reactants. For a reaction mechanism to be consistent with kinetic data, the experimentally derived rate law must match the rate-determining step or the overall contribution of the key steps in the proposed mechanism.

Transcript

00:01 So this is the information that we're given in this problem.

00:02 We're given an overall reaction here, which i have written in black right here, and then three elementary steps with the red one right here, step one being the slow step.

00:14 In other words, the re -determining step.

00:16 And so the first thing we need to do is we need to show that these elementary steps are actually, you know, what they actually add up to the reaction.

00:24 So we have to basically first we're going to just cross out things that exist both on the right and the, you know, what they actually add up to the reaction.

00:30 Left and then we'll add everything up and see that it should go to this overall reactions so looking first um uh pardon me i did actually see a mistake here in the what i've written here and i'll correct that here it's o i minus pardon me back to it the other reason i point that out is because we have an oh i minus on the right and an oi minus on the left so those cancel out we also see this hoi and this hoi on the left right and left cancel out it looks like there's nothing else that we can cancel out but let's add up so we have we should have one h22 one hydrogen peroxide and that's all we have on the left so check for that to be correct we have two h pluses and we do one two so that's good check right there we should have two i minuses and we do one two so that's correct on the right we should have one i2 and we do and two h2os and we do and so like that, we've shown that we all the elementary steps add up to the total reaction.

01:46 And that's what we're looking for.

01:48 Now, for the next question, what is the molecularity? since these are elementary steps, this is saying that all of the reactants are colliding in this reaction.

01:58 And so it's actually a really simple question.

02:00 We just count the number of reactions.

02:01 We have one, two.

02:03 So this reaction is bimolecular.

02:07 Second step, one, two, again, bimolecular.

02:11 I'll just say a brief like that.

02:13 And then we have one, two, three, trimal act there.

02:18 So that's a lot easier than it seems...

Please give Ace some feedback