Standard Article

Combustion Calorimetry

Thermal Analysis

  1. P. A. G. O'Hare1,
  2. Maria D. M. C. Ribeiro da Silva2,
  3. Manuel A. V. Ribeiro da Silva2

Published Online: 12 OCT 2012

DOI: 10.1002/0471266965.com031.pub2

Characterization of Materials

Characterization of Materials

How to Cite

O'Hare, P. A. G., Ribeiro, M. D. M. C. and Ribeiro, M. A. V. 2012. Combustion Calorimetry. Characterization of Materials. 1–15.

Author Information

  1. 1

    Green Valley, AZ, USA

  2. 2

    University of Porto, Department of Chemistry and Biochemistry, Faculty of Science, Portugal

Publication History

  1. Published Online: 12 OCT 2012

Abstract

In the absence of direct experimental information, one often must rely on knowledge of thermodynamic properties to predict the chemical behavior of a material under operating conditions. For such applications, the standard molar Gibbs energy of formation inline image is particularly powerful; it is frequently derived by combining the standard molar entropy of formation inline image and the standard molar enthalpy of formation inline image, often as functions of temperature and pressure. It follows, therefore, that the standard molar enthalpy of formation, inline image, is among the most valuable and fundamental thermodynamic properties of a material. This quantity is defined as the enthalpy change that occurs upon the formation of the compound in its standard state from the component elements in their standard states, at a designated reference temperature, usually (but not necessarily) 298.15 K, and at a standard pressure, currently taken to be 100 kPa.

Many methods have been devised to obtain inline image experimentally. Those include the so-called second- and third-law treatments of Knudsen effusion and mass-spectrometric results from high-temperature vaporization observations, as well as EMF results from high-temperature galvanic cell studies (Kubaschewski et al., 1993). Each of those techniques yields inline image for the studied process at a given temperature. To derive values of inline image, the high-temperature results for inline image must be combined with auxiliary thermodynamic information (heat capacities and enthalpy increments at elevated temperatures). Frequently, it turns out that the latter properties have not been measured, so they must be estimated (Kubaschewski et al., 1993), with a consequent degradation in the accuracy of the derived inline image. Furthermore, high-temperature thermodynamic studies of the kind outlined here often suffer from uncertainties concerning the identities of species in equilibrium. Another potential source of error arises from chemical interactions of the substances or their vapors with materials of construction of Knudsen or galvanic cells. All in all, these approaches do not, as a rule, yield precise values of inline image. Sometimes, however, they are the only practical methods available to the investigator.

Alternative procedures involve measurements of the enthalpies (or enthalpy changes) of chemical reactions, inline image of a substance and the elements of which it is composed. Experimentally, the strategy adopted in such determinations is dictated largely by the chemical properties of the substance and by the equipment available in the laboratory. The most obvious approach involves direct combination of the elements, an example of which is the combustion of gaseous H2 in O2 to form H2O. In the laboratory, however, it is often impossible under experimental conditions to combine the elements to form a particular compound quantitatively. An alternative, albeit less direct route has been used extensively for the past century or more, and involves measurements of the enthalpy change associated with a suitable chemical reaction of the material of interest. Here, the compound is “destroyed” rather than formed. Such chemical reactions have involved, inter alia, dissolution in a mineral acid or molten salt (Marsh and O'Hare, 1994) and the construction of an appropriate thermochemical cycle, thermal decomposition to discrete products (Gunn, 1972), or combustion in a gas such as oxygen or a halogen. This last method is the subject matter of this article.

Keywords:

  • combustion calorimetry;
  • static bomb calorimeter;
  • rotating bomb calorimetry