An adiabatic calorimeter was used to measure the enthalpy of solution of 1-octyl-3-methylimidazolium tetrafluoroborate (0.0035 mol·kg-1 to 0.02 mol·kg-1) in water and in aqueous sodium fluoride of different ionic strengths (0.1 mol·kg-1 to 0.43 mol·kg-1) at nominal temperatures of 298 K, 306 K, and 313 K. Two additional measurements of the enthalpy of solution of 1-butyl-3-methylimidazolium tetrafluoroborate (0.013 mol·kg-1) in water at 298 K are also reported. The present results lead to the standard-state changes of enthalpy and heat capacity for the solution process. The contribution of a methylene group to the enthalpy of solution of these ionic liquids was determined from the measurements and is shown to be in agreement with the value obtained from other classes of organic compounds. The enthalpy of solution increment for the methylene group is used to calculate the enthalpy of solution of the series of 1-alkyl-3-methylimidazolium tetrafluoroborates. Calculated standard-state heat capacity values for the aqueous solution process and the aqueous solute are also given. Potential micelle formation of 1-octyl-3-methylimidazolium tetrafluoroborate in water was examined.

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An adiabatic calorimeter was used to measure enthalpies of solution into water of sodium chloride (∼0.13 mol‚kg -1 ) at nominal temperatures of 298.15 K, 303.15 K, and 308.15 K and of potassium sulfate (∼0.039 mol‚kg -1 ) at nominal temperatures of 298.15 K and 303.15 K. The results for sodium chloride were compared to a previous equation of state so as to validate the use of values from that equation of state for calibration of, or checks on the accuracy of, solution calorimeters. Thermodynamic properties from the literature for the potassium sulfate + water system and the present measurements were used to generate equations that represented the thermodynamic properties of this system from the freezing point of the aqueous solution to 500 K. The measured values included in the fitted equations spanned the range of temperature of approximately 271 K to 530 K for K 2 SO 4 (aq) and 13 K to 854 K for K 2 SO 4 (cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of K 2 SO 4 (cr) from 0 K to near the orthorhombic to hexagonal transition at 857 K, (2) the change in chemical potential for both K 2 SO 4 and H 2 O in K 2 SO 4 (aq) as a function of temperature and molality, valid from 271 K to 500 K, from 0 mol‚kg -1 to the saturation molality, and to pressures of 40 MPa, and (3) standard-state properties for the aqueous solution process.

The specific conductance of p y r i d i n i u m HCI, N -m e t h y l p y r i d i n i u m chloride, N -m e t h y l p y r i d i n i u m bromide, 4-methylpyridinium bromide, and p y r i d i n i u m bromide, was measured as a function of temperature. The NMR spectra of the first three fused salts were also measured over the same temperature ranges. Correlations between conductance data and spectral data were found to exist.The experimental results indicate that the "friction" between the chloride and pyridinium ion is greater than between the bromide and the p y r i d i n i u m ion. The positive charge of the pyridinium ion seems to be localized on the nitrogen. In the pyridinium HC1 system the labile proton is probably contributing to the conductivity.

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A test substance with characteristics and properties similar to those of cellulose· based solid waste products is needed to calibrate calorimeters and combustors which will be routinely burning these materials to determine their calorific values precisely for use in commerce. Microcrystalline cellulose was found to be a good calibrant for this purpose. The enthalpy of combustion of microcrystalline cellulose ~H~ at (25 0q, and its estimated uncertainty, was determined to be -2B12.401±1.725 kllmol based upon the sample mass.A calculated heat of wetting correction of 1.514 kl Imol was applied to the combustion data.