A.J. Head

Thermodynamic properties of organic oxygen compounds 21. Enthalpies of combustion of benzoic acid, pentan-1-ol, octan-1-ol, and hexadecan-1-ol

Abstract The factors which govern the precision and accuracy of the results obtained using the electrically calibrated static-bomb calorimeter recently constructed in this Laboratory have been investigated and controlled. A precise value is reported for the energy of combustion of benzoic acid which is in close agreement with values obtained in two other laboratories where the energy of combustion of benzoic acid from the same batch (National Bureau of Standards 39i) has been measured. The enthalpies of combustion of pentan-1-ol, octan-1-ol, and hexadecan-1-ol have been determined. The enthalpies of formation in the gas-phase of the normal alkanols CnH2n + 2O have been shown to vary linearly with n for values of n = 2, 3, 4, 5, 8, 16.

Thermodynamic properties of organic oxygen compounds 41. Enthalpies of formation of eight ethers

Abstract Energies of combustion at 298.15 K by static-bomb calorimetry and enthalpies of vaporization at 298.15 K have been determined for the following ethers: methyl n -propyl, methyl n -butyl, methyl t -butyl, ethyl n -propyl, di- t -butyl, methyl n -decyl, methyl phenyl, and ethyl phenyl. A semi-automatic method for recording the temperature changes in combustion calorimetry and modifications to the LKB vaporization calorimeter are described. Standard enthalpies of formation in the ideal-gas state at 298.15 K for the eight ethers have been calculated from the results of these measurements. Best values of ΔH f 0 (g, 298.15 K) are tabulated for 15 aliphatic ethers and discussed in relation to molecular structure.

Thermodynamic properties of fluorine compounds 9. Enthalpies of formation of some compounds containing the pentafluorophenyl group

Abstract The energies of combustion of pentafluorobenzene, methylpentafluorobenzene, pentafluorophenol, and chloropentafluorobenzene have been determined using a rotating-bomb calorimeter. The sublimation pressures at temperatures near 25 °C of p -fluorobenzoic acid, pentafluorobenzoic acid, and pentafluorophenol have been measured by a transpiration method, and enthalpies of sublimation have been calculated from the results of these measurements. Enthalpies of formation in the gas state at 298 K (derived from these and previously published results) are reported for pentafluorobenzene, methylpentafluorobenzene, pentafluorophenol, chloropentafluorobenzene, and pentafluorobenzoic acid, together with a slightly revised value for hexafluorobenzene, and are discussed in terms of electrostatic interaction between the dipolar substituents of the benzene nucleus.

Thermodynamic properties of aliphatic halogen compounds 4. The enthalpy of combustion of 1,1,1,2-tetrachloroethane

Abstract The enthalpy of combustion of 1,1,1,2-tetrachloroethane at 298.15 K has been determined by rotating-bomb calorimetry. Arsenious oxide was used as the reducing agent in a tantalum-lined combustion bomb. The value − ΔH c o = (973.90 ± 1.28) kJ mol −1 was obtained from which − ΔH f o (l) = (193.45 ± 1.35) kJ mol −1 was derived.

Thermodynamic properties of organic oxygen compounds 22. Enthalpies of combustion of some aliphatic ketones

Abstract The energies of combustion of pentan-2-one, pentan-3-one, 3-methylbutan-2-one, hexan-2-one, hexan-3-one, 3,3-dimethylbutan-2-one, nonan-5-one, and undecan-6-one have been determined. The enthalpies of formation in the gas-phase of eight straight-chain alkanones C n H 2 n O have been shown to vary linearly with n over the range n = 3 to 11. The increment in δH f o (g, 298.15 K) per methylene group differs by a small but significant amount from that found in the n -alkanol series.

Thermodynamic properties of organic oxygen compounds 42. Physical and thermodynamic properties of benzaldehyde

Abstract The following properties of a purified sample of benzaldehyde have been measured: vapour pressure (311 to 481 K); density of liquid (293 to 490 K); heat capacity of crystals and liquid (13 to 425 K); enthalpy of fusion; triple-point, normal boiling, and critical temperatures; and enthalpy of combustion in oxygen. From the measurements, the enthalpy of vaporization, the entropy (crystal, liquid, and ideal gas); and the enthalpy of formation (liquid and ideal gas) have been calculated. Thermodynamic functions (0 to 1000 K) of the ideal gas have been calculated from a vibrational assignment and molecular dimensions.

A comparison of standard reactions for solution and combustion calorimetry II. Combustion-calorimeter measurements

Abstract The enthalpy of reaction of tris(hydroxymethyl)-aminomethane ( Tris ) with excess dilute hydrochloric acid has been compared with the enthalpy of reaction of sulfuric acid with excess sodium hydroxide at low and high concentrations. In the following paper, the enthalpy of the H2SO4+NaOH reaction at high concentration has been measured relative to the enthalpy of combustion of benzoic acid. Combination of the results permits deduction of the enthalpies of the H2SO4+dilute NaOH and Tris +HCl reactions, independent of the absolute accuracy of the electrical-heating calibrations of the solution calorimeter.

Thermodynamic properties of phosphorus compounds 3. The enthalpy of formation of aqueous orthophosphoric acid

Abstract The enthalpy of formation of aqueous orthophosphoric acid has been determined using a rotating-bomb calorimeter. White phosphorus, encapsulated in polyethylene, was burnt in oxygen and the products hydrolysed to orthophosphoric acid using perchloric acid at 50 °C, the combustion and hydrolysis reactions both being completed within the reaction period of a calorimetric experiment. From the results of these determinations and other thermal measurements, together with published heat capacities, the following value was calculated: δH 0 f (H 3 PO 4 in 40 H 2 O, 298.15 K) = − (1294.3 ± 1.6) kJ mol −1

The standard enthalpy of formation of ammonium nitrate and of the nitrate ion

Abstract The standard enthalpy of formation of ammonium nitrate in its stable reference state at 298.15 K has been derived from measurements of the energy of combustion of samples of hydrocarbon oil and polyethene sheet in the presence of ammonium nitrate. Under the conditions chosen, the last substance decomposed to N2(g), O2(g), and H2O(l); the only significant by-product found was HNO3·nH2O. Special care was devoted to preparation of the NH4NO3 sample in its stable state (crystalline form IV), free of water. Combination of the resulting value of ΔtHo with recent data on the enthalpies of solution and dilution of NH4NO3(cr, IV), together with key values from the CODATA compilation, gave ΔtHo(NO3−, aq) = −(206.81 ± 0.41) kJ mol−1.

Thermodynamic properties of phosphorus compounds 4. The energy of combustion of triphenylphosphine oxide: a test substance for the combustion calorimetry of organophosphorus compounds☆☆☆

Abstract The energy of combustion of triphenylphosphine oxide at 298.15 K has been determined by rotating-bomb calorimetry. Two series of measurements were carried out using firstly water, and secondly perchloric acid, as hydrolytic agent in the combustion bomb. The results of the two series were in very good agreement and the weighted mean value − Δu c o = (35789 ± 6.0) J g −1 was obtained for the reaction C 18 H 15 OP(c) + 22.5O 2 (g) = 18CO 2 (g) + (H 3 PO 4 + 6H 2 O)(1). Triphenylphosphine oxide fulfils the requirements of a reference material for the combustion calorimetry of organophosphorus compounds.