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(physical chemistry)
The measurement, interpretation, and analysis of heat changes accompanying chemical reactions and changes in state.



a branch of physical chemistry and a specific area of chemical thermodynamics concerned with the measurement and calculation of the heat effects of reactions, the heats of such phase transitions as vaporization, and the heats of other processes; also, the study of the heat capacities, enthalpies, and entropies of substances and physicochemical systems and the temperature dependence of these quantities.

The experimental side of thermochemistry is known as calo-rimetry, which entails the development of techniques for determining the properties listed above. Thermochemical measurements are performed with calorimeters.

The importance of studying heat effects and heat capacities was first pointed out by M. V. Lomonosov in the years 1752–54. The first thermochemical measurements were carried out by J. Black, A. Lavoisier, and P. Laplace in the second half of the 18th century. Calorimetric measuring techniques were refined in the 19th century through the work of such scientists as G. I. Gess (G. H. Hess), P. Berthelot, H. P. Thomsen, and V. F. Luginin. In the early 20th century, progress in thermochemistry was marked, on the one hand, by increases in the accuracy and temperature range of experiments and, on the other, by the establishment of links between the energy effects of processes, the structure of particles (atoms, molecules, ions), and the position of elements in D. I. Mendeleev’s periodic system. In addition, the number of substances that were investigated increased. In the mid–20th century, theories of thermochemistry came to be based on statistical concepts and concepts from quantum chemistry.

The difficulty and, sometimes, impossibility of directly measuring the heat effects of many processes often necessitates determinations through an indirect method, which is based on the fundamental law of thermochemistry—Hess’s law. These calculations employ standard heats of formation gsed_0001_0025_0_00017 of various substances. Standard heats of combustion are used for the reactions of organic compounds. Heats of formation gsed_0001_0025_0_00017 of chemical reactions may be recomputed at other temperatures using Kirchhoff’s equation. When the data required for a calculation are lacking, it is often necessary to resort to approximate relationships. These relationships make possible a determination of various energy properties of processes and substances on the basis of composition and structure, as well as by analogy with previously studied substances and processes.

Data from thermochemical studies, together with experimentally established relationships, are used to compute the heat balance of technological processes, investigate the heat value of fuels, calculate chemical equilibria, and determine the correlations between the energy properties of substances and the substances’ composition, structure, stability, and reactivity. In conjunction with other thermodynamic properties, thermochemical data make it possible to choose the optimal conditions for the production of chemicals.

Broad advances have been made in the thermochemistry of solutions, specifically, in determining heat capacities, heats of solution, mixing, and vaporization, and the dependence of these quantities on temperature and concentration. When these quantities are known, the properties of individual components may be found, and the heats of solvation and the heat effects of other processes may be calculated. This information is important as a basis for theories on the nature and structure of solutions. Thermochemical methods are employed in, for example, colloid chemistry and studies of biological processes.


Skuratov, S. M., V. P. Kolesov, and A. F. Vorob’ev. Termokhimiia, parts 1–2. Moscow, 1964–66.
Mishchenko, K. P., and G. M. Poltoratskii. Voprosy termodinamiki i stroeniia vodnykh i nevodnykh rastvorov elektrolitov. [Leningrad] 1968.
Experimental Thermochemistry, vols. 1–2. New York-London, 1956–62.
Calvet, E., and H. Prat. Mikrokalorimetriia. Moscow, 1963. (Translated from French.)
Mortimer, C. Teploty reaktsii i prochnost’ sviazei. Moscow, 1964. (Translated from English.)
Benson, S. Termokhimicheskaia kinetika. Moscow, 1971. (Translated from English.)
Stull, D., E. Westrum, and G. Sinke. Khimicheskaia termodinamika organkheskikh soedinenii. Moscow, 1971. (Translated from English.)


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Wilhoit, "ThermoML--an XML-based Approach for Storage and Exchange of Experimental and Critically Evaluated Thermophysical and Thermochemical Property Data.
This is significant because the thermochemical model does not require tunneling electrons to damage the oxide (only the applied gate field is required).
In this paper the inhomogeneous thermochemical behavior, during cure, of an unsaturated polyester resin through the thickness is reported.
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Save Stratford, a network of residents concerned about toxic waste in town, has been pushing the EPA to determine whether thermochemical conversion could be used to detoxify waste at the Raymark Superfund site and other brownfields in town.
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Enerkem Inc, a company that develops biofuels and chemicals from waste, with its proprietary thermochemical technology, has named Carl Rush as its director.
A broad range of options are explored and assessed, including familiar renewable sources like wind and solar, as well as biofuels, nuclear, hydrogen, synthetics, photochemical, thermochemical, atmospheric carbon dioxide recycling, and biological sources.
The collaboration will include how algae can add energy content to other feedstocks such as woody and herbaceous materials, which are already being configured for biochemical and thermochemical upgrading for energy production.
The topics are the chemistry, resources, and logistics of biomass; the kinetics and microbiology of biological processes; anaerobic digestion for biogas production; biological processes for ethanol production and butanol production; the chemical conversion process for biodiesel production; and the thermochemical conversion of biomass to power and fuels.
In recent years, thermochemical treatments--and especially ionitriding (also known as plasma nitriding) have gained a wide usage in machines manufacturing processes, due especially to the advantages they offer in terms of improved hardness and strength of the superficial layer of parts and consequently this topic has been widely discussed by various authors (Ruset, 1991; Rie, 1999; Tracton, 2007).