Margret Månsson

Test substances for bomb combustion calorimetry. p-Chlorobenzoic acid

Abstract Enthalpies of combustion were determined on two different samples of p-chlorobenzoic acid in three series of measurements under widely varied conditions. Three different rotating-bomb calorimeters were used. The enthalpies of combustion, ΔHoo obtained were −(732.07±0.18),−(732.02±0.25), and − (732.06±0.20) kcal th mol −1 respectively, for the reaction with (HCl·600H2O)(1) as the chlorine-containing product in the final state. p-Chlorobenzoic acid is recommended as a test substance for bomb combustion calorimetry of organic chlorine compounds. A value for the enthalpy of solution of carbon dioxide in pure water was derived from the temperature dependence of existing solubilities. A detailed computation form for the Washburn corrections for organic chlorine compounds is given.

Enthalpies of vaporization of some 1-substituted n-alkanes

Abstract Enthalpies of vaporization at 298.15 K have been determined calorimetrically for some 1-substituted straight-chain alkanes. The results are: Compound ΔH v o /kJ mol −1 Compound ΔH v o /kJ mol −1 1-octene 40.27 ± 0.20 1-bromooctane 55.77 ± 0.25 1-decene 50.43 ± 0.20 1-bromododecane 74.77 ± 0.38 1-dodecene 60.78 ± 0.20 1-bromohexadecane 94.4 ± 1.5 1-hexadecene 80.25 ± 0.42 methyl pentanoate 43.10 ± 0.06 1-hexanol 61.85 ± 0.20 methyl hexanoate 48.04 ± 0.12 1-heptanol 66.81 ± 0.20 methyl heptanoate 51.62 ± 0.48 1-octanol 70.98 ± 0.42 methyl octanoate 56.41 ± 0.50 1-nonanol 76.86 ± 0.75 methyl nonanoate 61.99 ± 0.41 1-decanol 81.50 ± 0.75 methyl decanoate 66.75 ± 0.57 1-dodecanol 91.96 ± 0.59 methyl undecanoate 71.37 ± 0.30 1-tetradecanol 102.2 ± 2.3 methyl dodecanoate 77.17 ± 0.56 1-mercaptodecane 65.48 ± 0.54 methyl tridecanoate 82.68 ± 0.84 methyl tetradecanoate 86.98 ± 0.94 1-chloropropane 28.50 ± 0.21 methyl pentadecanoate 93.49 ± 0.94 1-chlorododecane 71.93 ± 0.32 1-chlorohexadecane 91.8 ± 1.1 An analysis of available data shows that the enthalpy of vaporization for members within seven homologous series, XC m H 2m + 1 , can be expressed as ΔH v o (X, m ) = A x + B x m .

Enthalpies of combustion and formation of acetonitrile

Abstract The enthalpy of combustion at 298.15 K has been determined and the standard enthalpy of formation for the compound in the liquid state derived as ΔH f o (l) = (40.56±0.40) kJ·mol −1 . The results of recent work on acetonitrile by Barnes and Pilcher are summarized. The weighted mean from the two investigations becomes ΔH f o (l) = (40.59±0.30) kJ·mol −1 . An attempt has been made to reduce literature values for the enthalpies of vaporization ΔH vap for the lower n -alkanenitriles to values referring to the ideal-gas state, ΔH vap o . The resulting standard enthalpy of formation for acetonitrile in the gaseous state is ΔH f o (g) = (74.04±0.37) kJ·mol −1 .

Non-bonded oxygen-oxygen interactions in straight-chain compounds☆

Abstract Enthalpies of combustion and vaporization at 25.0 °C have been measured for some saturated, straight-chain oxa-compounds. Enthalpies of formation at 25.0 °C have been derived for the compounds in the liquid and gaseous states. The results are: ΔH f o (l)/kJ mol −1 ΔH f o (g)/kJ mol −1 3,5-Dioxaheptane −450.4 ± 0.8 −414.8 ± 0.8 3,5,7-Trioxanonane −625.8 ± 1.0 −581.1 ± 1.0 3,5,7,9-Tetraoxaundecane −794.6 ± 1.2 −741.0 ± 1.4 3,5,7,9,11-Pentaoxatridecane −968.4 ± 1.4 −905.9 ± 1.9 3,6-Dioxaoctane −451.4 ± 1.0 −408.2 ± 1.0 The compounds with next-nearest-neighbour oxygen atoms are shown to be stabilized by (16.9 ± 0.2) kJ mol−1 per OCO interaction compared with monoethers. The results are summarized in terms of an Allen bond energy scheme and the OCO interaction parameter is calculated. The Allen scheme fails in predicting the ΔHfo(g) value for 3,6-dioxaoctane, which has an “apparent strain” of 10 kJ mol−1. The enthalpy of isomerization for CH2OCH2CH2O-(g) = CH2OCH2OCH2-(g) has been calculated, and is in good agreement with that for 1,4-dioxane(g) = 1,3-dioxane(g). Strain in a number of six-membered, cyclic oxa-compounds is discussed in the light of the results of this investigation.

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.

A 4.5 cm3 bomb combustion calorimeter and an ampoule technique for 5 to 10 mg samples with vapour pressures below approximately 3 kPa (20 Torr)

A micro combustion calorimeter, internal bomb volume 4.5 cm3, has been built and tested. The calorimeter, intended for sample sizes around 10 mg, can be calibrated electrically as well as by combustion of benzoic acid. The standard deviation of the mean of a series of five experiments on 10 mg samples is ordinarily less than 0.02 per cent. The ratio of the energy equivalents, derived from benzoic acid and electrical calibrations, is 1.00019 with an uncertainty of ±0.00034 at a 95 per cent confidence level. The energy of combustion of 1,8-dimethylnaphthalene has been determined and is in good agreement with a recent macro determination. An ampoule technique for 5 to 8 mg solid samples with vapour pressures below approximately 20 Torr has been developed. The calorimeter fits the LKB 8700 precision calorimetry system.

Enthalpies of combustion and formation of ethyl propionate and diethyl carbonate

Abstract Enthalpies of combustion and vaporization at 298.15 K have been measured for ethyl propionate and diethyl carbonate. Enthalpies of formation at 298.15 K have been derived for the compounds in the liquid and gaseous states. The results are: ΔH f o (l)/kJ mol −1 ΔH f o (g)/kJ mol −1 Ethyl propionate −502.7 ± 0.7 −463.6 ± 0.7 Diethyl carbonate −681.5 ± 0.8 −637.9 ± 0.8 The sum of the Allen bond-energy scheme parameters ( Γ oc d o d + Δ coo d ) for esters has been calculated. The stabilization energy calculated for ethyl propionate is 80 kJ mol −1 and for diethyl carbonate 129 kJ mol −1 .

Thermochemistry of nine diazenes (azo compounds)

Abstract Enthalpies of combustion of five diazenes and enthalpies of vaporization of nine diazenes have been measured. The experimental results yield values of the enthalpies of formation for the condensed and gaseous states of these compounds: di- n -propyldiazene; di- i -propyldiazene; di- t -butyldiazene; t -butyl(1,1,3,3-tetramethylbutyl)diazene; di(1,1,3,3-tetramethylbutyl)diazene; 1,1,3,3-tetramethyltrimethylenediazene; 1,1,4,4-tetramethyltetramethylenediazene; 2,3-diazabicyclo[2.2.1]heptene-2; and 1,4-dimethyl-2.3-diazabicyclo-[2.2.2]-octene-2.

The energy of combustion of succinic acid

Abstract The energy of combustion of a thoroughly dried sample of succinic acid was measured by oxtgen-bomb combustion calorimetry, with the result: ΔU o o (298.15 K ) M = −(3020.86±0.54) cal th g −1 from six combustions. The results of 15 previous investigations on the energy of combustion of succinic acid were critically reviewed and recalculated to 298.15 K and standard state conditions. The weighted mean values for succinic acid are: ΔU o o M = −(3020.55±0.38) cal th g −1 ; ΔU o o = −(356.69 7 ±0.045) kcal th mol −1 ; ΔH o o = −(356.40 1 ±0.045) kcal th mol −1 ; ΔH t o = −(224.75±0.13) kcal th mol −1 . The optimum procedures for use of succinic acid as a test substance in combustion calorimetry are discussed.

Enthalpies of formation of mono- and diammonium succinates and of aqueous ammonia and ammonium ion☆

Abstract The energies of combustion of mono- and di-ammonium succinates were measured by rotating-bomb combustion calorimetry. Enthalpies of solution of the two salts and of succinic acid were obtained by solution calorimetry. The results were used with other data to evaluate enthalpies of formation as follows: State ΔH f o (298.15 K)/kcal th mol −1 Monoammonium succinate c −255.22±0.21 Diammonium succinate c −282.67±0.18 NH 4 + aq −31.820±0.045 NH 3 aq −13.395±0.045