Thermochemistry and the Thermodynamic Properties of Substances

Abstract

This review concerns a branch of physical chemistry that had its begin­ ning in the period when chemistry emerged as a recognized branch of natural philosoph y. In fact, one of the early thermochemists was "the father of chem­ istry," Antoine Lavoisier , whose calorimetric researches included dete rmina­ tions of the heats of combustion of hydrogen , charcoal, phosphorus, candle wax, and olive oil and the heat of reaction of potassium nitrate with char­ coal. Thus, the field of the rmochemistry is at least 170 years old. The related field of chemical the rmodynamics grew up at its side as the laws of thermo­ dynamics were discovered and consolidated . These fields, despite their age, st ill attract able investigators with a multitude of challenging problems, as witnessed by the number of rese arch publications in the period covered by this rev iew. The reason for the continu ing, and perhaps increasing, interest in thermo­ chemistry and chemical thermodynamics is not hard to see. The long-range aim is to obtain accurate values of standard heat and free energy of forma­ tion of all che mical substances of intere st, so that accurate values of standard heat of reaction and equil ibrium constant may be calculated for any chemical reactions of interest. When it is remembered that "chemical substances of interest" may include any of the half million or so compounds now known and the hundreds discovered each year, it is seen that the endeavor has just begun . Moreover , if the restriction of "standard" is removed and replaced by "under conditions of intere st," the ende avor is compounded manyfo ld. The accumulation of data on the heat and free energy of formation of chemical substances is not, however , a matter of routine dete rminatio n, by established meth ods , of more numbers to fill more pages of tables . On the contra ry, the acquisition of such data ever poses new problems to test the abilities of the ablest experimenter , and the interpretation of experimental observations often calls for a high degree of theoretical ingenu ity. Furthermore , the co­ products of many the rmodynamic studies, such as a clearer insight into the detailed structure and energetics of molecules and crystals, may seem more rewarding than the additions to the store of chemical the rmodynamic infor­ mation that come from the studies . The contributions of the rmodynamics to the study of molecular and crystal structure, and indeed to nearly all fields of physical chemi stry, are important topics, which, however , are more appro­ priate to reviews of these other fields and will not be conside red here. I This review covers recen t publicat ions on thermochemistry and chemical thermo ­