Flame combustion calorimetry oxygen

Flame combustion calorimetry in oxygen is used to measure the enthalpies of combustion of gases and volatile liquids at constant pressure [54,90]. Some highly volatile liquids (e.g., n-pentane [91]) have also been successfully studied by static-bomb combustion calorimetry. In general, however, the latter technique is much more difficult to apply to these substances than flame combustion calorimetry. In bomb combustion calorimetry, the sample is burned in the liquid state and must be enclosed in a container prior to combustion. Encapsulation may be difficult, because it is necessary to minimize the amount of vaporized compound inside the container as much as possible. In addition, volatile liquids tend to burn violently under a pressure of 3.04 MPa of oxygen, which leads to incomplete combustion. These problems are avoided in flame combustion calorimetry, where the sample is carried to the combustion zone as a vapor and burned under controlled conditions at atmospheric pressure. 

The study of reaction 7.73 is one of the most important thermochemical experiments ever made, and it will be briefly analyzed here to illustrate the flame combustion calorimetry method. The application of flame combustion calorimetry to hydrocarbons and other organic compounds containing oxygen, nitrogen, or chlorine is covered in detail in the review by Pilcher [90]. 

Much of the discussion of oxygen flame calorimetry presented in section 7.3 is directly applicable to fluorine flame calorimetry. As in the case of bomb calorimetry, however, the special properties of fluorine combustion systems and problems associated with handling fluorine require a somewhat different experimental method [109,115,116]. Thus, for example, a metal burner should be used. Also, the fact that the mixing of many gases with F2 may lead to spontaneous ignition hinders the use of a premixed flame. Fluorine combustion calorimetry has been used to study the thermochemistry of important reactions, such as... 

G. Pilcher. Oxygen Flame Calorimetry. In Experimental Chemical Thermodynamics, vol. 1 Combustion Calorimetry, S. Sunner, M. Mansson, Eds. IUPAC-Pergamon Press Oxford, 1979 chapter 14. 

Fluorine flame calorimetry is a logical extension of oxygen flame calorimetry in which a gas is burned in excess of gaseous oxidant (214). The decision does not reach that of the oxygen flame calorimeter in which, for example, Affj(H20) was determined with a standard deviation of 0.01%. Combustions of H2, NH3 (8), and fluorinated hydrocarbons are typical applications, but the uncertain nonideality corrections of HF(g) prevent full realization of the inherent accuracy. 

When hydrocarbons or other organic compounds are burnt in a flame calorimeter it is often necessary to pre-mix the gas with oxygen to increase flame stability and obtain complete reaction. However, if the optimum proportion of oxygen is exceeded the flame temperature becomes too high and thermal decomposition with deposition of carbon occurs below the jet. Since the combustion takes place at constant pressure close to 1 bar, the enthalpy of combustion is measured under conditions near to those of the standard states. Flame calorimetry has the advantage that enthalpies of combustion are obtained for the gaseous state without the necessity of measuring enthalpies of vaporization in separate experiments and, moreover, completeness of combustion can be established by determination of both the water and the carbon dioxide produced. 

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