Sciencemadness Discussion Board

Q about rate constant and thermodynamic kinetic problem w/o experimental data

SunriseSunset - 16-10-2015 at 00:29

Is it ever possible to come up with a reaction rate solution and activation energy solution to know just how long and what temperature a certain experiment should happen as, without experimental data?

What do you need to know in order to do that, and do they ever teach it in school? Or does organic chemistry always require 3 or more trial runs to plug in experimental data and figure out rate constants and reaction rates and activation energies? If so, what are the things that I would have to learn in order to do this myself?

Might anyone be able to help me out with this problem, it would help a lot if I knew a strict curriculum to follow to be able to solve these problems on my own.

For example the reaction of 1,4-dihydroquinone with H2O2 and iodine catalyst in 91% isopropyl alcohol as the solvent (to yield 1,4-benzoquinone), All I know so far is that I would have to collect experimental data from trial runs to determine a rate constant to use, and I would also have to know the mechanism for the reaction but what do I need to know in order to figure that stuff out just on paper alone before ever conducting the experiment? Are there any main things that any of you here use to perform these types of calculations?

Thanks

I want to find out what things I should start learning, and at what point of learning these things minimum should I begin to form my understanding, without getting too side tracked and distracted by other topics that aren't included for having a understanding decent enough to apply on my own experiments

[Edited on 16-10-2015 by SunriseSunset]

Sulaiman - 16-10-2015 at 02:21

from the very little that I have learned so far
I doubt that anything less than a quite complex mathematical model would help
I say this mainly because when I scale up an experiment it usually reacts quicker, so it's not just chemistry but volume, shape etc. of reaction vessel affects rate, and of course as most reaction rates are temperature sensitive you'd have to model thermal masses etc.
So one or two trial runs is probably easier and quicker.

SunriseSunset - 16-10-2015 at 05:57

Concentration of reactants make more of a difference on reaction rate than scaling things up or down. That much I understand, makes sense.

blogfast25 - 16-10-2015 at 06:59

Quote: Originally posted by SunriseSunset  

I want to find out what things I should start learning, and at what point of learning these things minimum should I begin to form my understanding, without getting too side tracked and distracted by other topics that aren't included for having a understanding decent enough to apply on my own experiments



To answer some of your questions higher up, as far as I know it is not yet possible to derive reaction rate constants and activation energies merely from theory, only from experiment.

To form an understanding I'd recommend to study the following concepts:

1) Thermochemistry: thermodynamics applied to chemical reactions.
2) Collision theory: understand reaction kinetics, including activation energy and catalysis at the molecular collision level.

In addition, a minimum of Quantum Chemistry should also help.

[Edited on 16-10-2015 by blogfast25]

annaandherdad - 16-10-2015 at 07:41

It is possible to calculate reaction rates, but the calculations are not simple and the accuracy may not be as high as you would like. Here is one reference:

W. H. Miller, J. Chem. Phys. 61, 1823 (1974)

For further references you can search on "transition state theory" in Google Scholar.

blogfast25 - 16-10-2015 at 08:13

Quote: Originally posted by annaandherdad  
It is possible to calculate reaction rates, but the calculations are not simple and the accuracy may not be as high as you would like. Here is one reference:

W. H. Miller, J. Chem. Phys. 61, 1823 (1974)

For further references you can search on "transition state theory" in Google Scholar.


Do you have the full text? As ever, the abstract doesn't tell you that much.

annaandherdad - 16-10-2015 at 08:17

I'll get it to you later. I don't have access to it where I am now.

blogfast25 - 16-10-2015 at 08:25

Quote: Originally posted by annaandherdad  
I'll get it to you later. I don't have access to it where I am now.


Thank you.

Polverone - 16-10-2015 at 10:03

The Green research group at MIT is working on models for similar problems: http://cheme.scripts.mit.edu/green-group/

Their software is open source: http://reactionmechanismgenerator.github.io/

You might be interested in the CanTherm component.

Their open software relies on some closed-source software though, notably Gaussian for performing individual quantum chemistry calculations. It's one of those things that I've wanted to try fixing, one of these days.

EDIT: See the "model chemistry" referenced in their docs? http://reactionmechanismgenerator.github.io/RMG-Py/users/can...

The G3 and CBS-Q3 models they mention are composite thermochemical models of the sort I'm working on implementing in open source: https://www.sciencemadness.org/whisper/viewthread.php?tid=63...

[Edited on 10-16-2015 by Polverone]

MeshPL - 16-10-2015 at 11:21

Here, where I live, there is a country-sized chemistry competition for high-schools. This year, one of task for first, preliminary stage is about partialy about reaction rate. The participants are supposed to sketch the chart, of substrate concentration, product concentration and reaction rate dependancy on time. The reaction is 2SO3 <-> 2SO2 + O2. Equilibrum constant, final SO2 and O2 concentrations and temperature are known.

I assume that "sketch" means "draw it rougly correct" cause for the amount of knowledge you have here, when you leave highschool here you barely know about reaction constant. And preliminary stage isn't suppose to concern anything but mostly what is taught in highshools.

annaandherdad - 16-10-2015 at 14:26

Here is the Miller article.

Attachment: Miller.JCP.61.1823.1974.pdf (1.2MB)
This file has been downloaded 483 times

blogfast25 - 16-10-2015 at 15:39

Thanks. Downloaded.