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Name: Alison D.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 1/9/2004


Question:
What are the methods available for measuring the rate of a chemical reaction?


Replies:
There are literally thousands of methods for measuring the rates of chemical reactions, depending upon a large number of variables -- how fast is the reaction, is it a gas phase, liquid phase, solid phase, or mixed phases -- to mention just a few. In principle, any chemical or physical change that occurs as the reaction proceeds can be used to measure its rate. This could be pH, color, volume, temperature, pressure, -- the list is very long. You can find out some specific methods if you look up a book on "chemical kinetics" or even an introductory text on physical chemistry in the library. You might also do a "Google" search on terms like "rate(s) of chemical reaction" on the Internet.

Vince Calder


Alison,

Your question is not easy to answer because there are so many kinds of chemical reactions. Allow me to describe the bottom-line approach. For example in a hypothetical reaction like this:

A + B ===> C + D

We can measure the rate at which reactants (A and B) become products (C and D) by measuring how fast A (or B) disappears and / or how fast C (or D) appears in the reaction system. This is done by measuring the amounts (concentrations) of the reactants and / or products as the reaction proceeds.

This means that we must have a way to sample (or otherwise detect changes in) the contents of the reaction vessel while the reaction is in progress. That may or may not be easy because some reactions can be exceedingly fast or agonizingly slow.

Thus, the approach taken must consider the properties of the reactants and products and the overall nature of the process under study.

Regards,
ProfHoff 761


If the reaction causes a color change, then just watch this with instrumentation.

If the pH changes, things like this, then watch with a meter.

You could occasionally take sample from the reaction chamber and run the samples through a chromatography system, which separates out the parts. At first there will be only reactants. But as time goes on, and you come back for more samples, perhaps a new signal will begin to show up, the product. This might be useful for a slower reaction, where you have time to do all this.

Maybe the reaction releases heat, well watch the system warm up over time.

Many ways, but you have to narrow it down based on the reaction.

Steve Ross



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