Introduction

We have had quite enough theoretical discussion for now. Let's see how to get some numbers into our equations so as to be able to calculate something useful. Welcome to the world of experimental thermochemistry.

In this chapter we will have a look at a few of the ways in which the thermodynamic parameters we have derived are measured; i.e., where the numbers in the tables and databases come from. A deep knowledge of this subject is not necessary in order to use thermodynamics to model chemical, geological, or environmental systems, in the same sense that a knowledge of a composer's life and times is not necessary to enjoy his or her music. But it does enrich the experience, and in the case of using thermodynamics, such knowledge does serve to make the user conscious of the many, many reasons why his or her data might be incorrect. It enables the user to truly believe in the “modeler's motto” – never trust your data absolutely.

Thermochemical data are produced for the most part by dedicated scientists, who devote a good part of their lives to tracking down elusive sources of error, and devising ever-improved methods for determining nature's fundamental parameters as defined by thermodynamic theory. When determined by independent methods and/or independent laboratories, the results are often satisfyingly in agreement, but almost as often they are not, meaning that there is some source of error, and identifying it can take a lot of discussion (perhaps arguments would be a better term) and a long time.