View source for Talk:Chemical reaction kinetics

To: Referees of article “Chemical Kinetics”

From: Dick Field

Date: October 9, 2008

Re:  Revision of “Chemical Kinetics”

Thanks for your efforts!  I have carefully considered each and every of your comments and have made some change in response to each.  A number of comments were common to referees B and C.  I believe the article is much improved as a result of your suggestions.

Referee B.  I have tried to make the article more accessible to undergraduates.  I have put in all of the definitions you suggested, and in general you will find a response to each of your comments.  In most cases I simply did as you suggested.  I also tried to make a number of explanations more accessible, largely on the basis of your and another referee’s comments. 

The article was originally written for researchers. However, I think more than a half of my junior-level physical chemistry students could understand it if they wished to, although most would lack the maturity to actually apply the material to other systems.  It would be nice to pass through a sequence of simple examples as you suggest, but space is limited.  The article is now about 10% longer than the original, which I felt was near the maximum size for a Scholarpedia article.

The figure axis markings have been cleaned up as you suggested, although the new figures may not be inserted into the text by the editor until tomorrow (Friday, 10/10). Because of a peculiarity of the Wiki software,  it may be necessary to refresh your browser (control-R on Windows) to see the revised fogures.  The addition of noise in Figure 2 is explained more carefully.

Referee C.  Thank you for your particularly careful reading of “Chemical Kinetics”.  I have responded to each of your detailed comments, and I have developed several of your suggestions in a general polishing of the document.  Your comments remain embedded in the text for your reference.




My main concern is really just a suggestion to include more definitions/explanations, if the article is aimed at undergraduates. However, the article can be accepted as is if it is intended for a more general readership.

Opening section:
Is it necessary to include “as expressed in sometimes nonlinear differential equations” in the opening line of the article? Without this line it may be more immediately obvious to the undergraduate that kinetics links rates to mechanism.

Introduction:
Should Reaction Coordinates be plural in Figure 1? 

It might be useful to define the term “molecularity” after reaction 1 (i.e. along the lines of the number of species involved in the collision) and to mention that the rate constant is sometimes referred to as the rate coefficient.  

Elementary reaction:
Again it depends on who this article is aimed at, but a general definition of order and overall order (in terms of exponents in the rate equation) would be useful, perhaps in a separate box.

Seems a little odd to state a product of concentrations, which doesn’t have units of time in it, “defines the frequency”. Might be better to say “is related to the frequency”? Could add that k is the related to the number of effective collisions (i.e. that result in products).

Case of personal preference, but I would write the axis in Figure 2 as (10-9 M) or (nM) rather than /1 x 10-9.

It’s perhaps not necessary to state Figure 2 is simulated in the main text but say something along the lines of “typical profiles of how the species are expected to vary in experiments are shown in Figure 2. Setting x = …”. The figure legend could explain that the profiles are obtained from simulations with 5% noise and include the parameter values.

Stoichiometry and reaction rates:
A general definition of rate in terms of stoichiometric coefficients might be useful at this point, perhaps in a separate box.

Determination of the rate expression:
I prefer the term “pseudo order” to “flooding”.

Complex mechanisms:
In order to make it clear that M6 and M7 are elementary, perhaps write before the list that the overall reaction 2 is given by the sum of the elementary reactions: and in the list write 3 x (HOBr + H+ = H2OBr+)   etc. Writing it as 3HOBr.. I guess implies that the rate is given by [HOBr]3.

I prefer the term “pre-equilibrium approximation” to “equilibrium approximation” where the pre refers to rapid equilbria preceding a reaction (usually a fast acid-base process yielding a reactive species).


General comments:

- Please use "reaction" everywhere instead of "rxn"
- A better description is needed how 5% error was added to the simulated curve. Did the assumed noise have uniform distribution? Or a truncated normal distribution? How was the 5% defined?
- I have not met term "flooding" before in this context. The usual term is "pool component approximation"
- I suggest the application of terms "pre-equilibrium approximation" or "fast equilibrium approximation" and "quasi-staedy-state approximation (QSSA)"
- Let you divide both sides of reactions M6 and M7 by 3. M8 could be derived as 
M8=M1+M2+M3+M4+M5+3*M6+3*M7 
- My greatest concern is that the example based on reactions M1 to M7 is too complicated for a beginner. I suggest the introduction of the kinetic simplification approximations on a series of simpler examples and THEN could this complex example discussed.