Skip to main content Accessibility help
×
Hostname: page-component-78c5997874-s2hrs Total loading time: 0 Render date: 2024-11-13T01:04:10.160Z Has data issue: false hasContentIssue false

6 - Structural considerations in the calculation of reaction rates

Published online by Cambridge University Press:  18 December 2009

Raphael D. Levine
Affiliation:
Hebrew University of Jerusalem
Get access

Summary

We address the question that every chemist asks: given thermal reactants, how do you compute the rate of crossing the barrier toward the products? We seek to cast the answer using traditional tools and, specifically, the structure of the system at the barrier. Using just one, physically realistic, approximation, transition state theory enables us to do that. The theory identifies a bottleneck for the reaction and computes the rate of passage through it.

The success of transition state theory inspires us to do more. We shall, but we require additional assumptions to be made at each point where we seek a generalization. The most pressing reasons for doing this are that there may be more than one barrier separating the reactants and products and that there can be multiple reaction paths. The case of the O2 + C2H5 reaction, shown in Figure 5.6, represents the norm rather than the exception. Transition state theory allows us to compute the rate of barrier crossing, but to get to the products we may need to cross several barriers and/or take different paths. It is for this reason that quantum chemists have grown proficient in computing the structures at each barrier (and each hollow). But we still need to know how to compound the effects of multiple bottlenecks to obtain the overall reaction rate – and this task calls for either dynamical computations as in Chapter 5 or for an additional assumption as introduced in Section 6.2.

Type
Chapter
Information
Publisher: Cambridge University Press
Print publication year: 2005

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Save book to Kindle

To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Available formats
×

Save book to Dropbox

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.

Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

Available formats
×