A bomb calorimeter determination of the heats of formation of nitrous oxide and carbon dioxide

Abstract

In the course of a specific heat investigation at the National Physical Laboratory the need arose for an accurate knowledge of the heat of formation of nitrous oxide and since the published values of this constant differed widely it was decided to make a new determination.The work was undertaken by both the Physics and Engineering Departments of the National Physical Laboratory, and, whereas the former used a con tinuous flame method* involving combustion at constant pressure, the latter adopted the explosion method and a constant volume reaction.I t is the purpose of this paper to give an account of the results obtained by the explosion method.The mode of attack is already familiar and consisted, in this investigation, in exploding mixtures of the approximate composition 3C0 -j-2N20 and 3CO -j-0 2 and ascribing the difference in their heats of reaction to the splitting up of the 2NaO into 2N2 and 0 2. Subsequently a series of experiments was made on the mixture 3H2 -(-2N20 and its heat of reaction was compared with th at of the calibration mixture 3H 2 + 0 2. The result confirmed the value already obtained from the CO experiments.A reference has just been made to the calibration mixture and it should be pointed out at once th at the heat capacity of the calorimeter was determined by exploding 3H2 -f-0 2 mixtures in it, and hence the values given for the heats of formation of N 20 and C 0 2 are based on the heat of formation of H 20 (liquid) which has been taken as 68,320 gm. cal.i3° a t constant pressure and at 25° C.The accuracy with which the required heat of formation can be determined depends on the precision with which measurements can be made of the masses of the gases taking part in the reaction and the quantities of heat evolved. For the measurement of the latter the bomb calorimeter shown in fig.

Active Thermochemical Tables: The Adiabatic Ionization Energy of Hydrogen Peroxide

“…An excellent example of this is the dissociation energy of carbon monoxide, which ultimately plays a role in determining the enthalpy of formation for the carbon atom, clearly a quantity of fundamental importance. It transpires that the long-quoted standard enthalpy of formation of the carbon atom (711.49 ± 0.45 kJ mol –1 at 0 K; 716.68 ± 0.45 kJ mol –1 at T = 298 K from the CODATA compilation) relies solely on the bond dissociation energy of carbon monoxide (CO) (as well as the thermochemistry of COwhich was determined by considering experimental calorimetry, − the study of high-temperature equilibrium of CO, CO 2 , and O 2 , , as well as the Boudouard reaction involving the equilibrium of CO, CO 2 , and graphite , and that of the oxygen atom). The CODATA value for D 0 (CO) is taken from a 1955 study of predissociation of CO (B 1 Σ + ) by Douglas and Møller, which was originally intended to distinguish between the contending high (∼11 eV) or low (∼9 eV) estimates of the dissociation energy favored by, among others, Pauling and Herzberg (low values) as well as Kistiakowsky and Brewer (high values).…”