Heat Capacity Of Liquid Phase Research Articles

The heat capacity of fluorinated propane and butane derivatives by differential scanning calorimetry

The constant pressure liquid-phase heat capacities of 21 hydrogen containing fluorinated propane and butane derivatives and one fluorinated ether (CF3OCF2H) with boiling points ranging from -34.6° to 76.7°C have been measured to 3% accuracy by differential scanning calorimetry at 40°C. The measurements are needed to help identify alternative refrigerants and blowing agents that do not deplete the stratospheric ozone layer. The DSC method has two significant advantages for this purpose, which are: (i) only small samples (less than 100 mg) are required, and (ii) the instruments are available in many laboratories and can be used for the heat capacity measurement of liquids with subambient boiling points without modification or special accessories.

Concerning the shape of a growing dendrite

Time-independent growth of a dendrite with a nonisothermic surface is considered. The Gibbs-Thomson correction, kinetic supercooling and the curvature correction under conditions of thermal balance are taken into account. The solid- and liquid-phase heat capacities need not be equal. We obtain lower estimates for the degree of difference of the dendrite shape from paraboloidal (parabolic), valid for any — not necessarily small — values of the parameters (supercooling, surface tension, etc.).

Narrow-boiling distillates of coal liquefaction products: 2. Heat capacities

The liquid phase heat capacities of narrow-boiling-range distillates from coal liquefaction products were predicted using group contribution, corresponding states and curve-fitting procedures. These predictions were compared to experimentally determined values. The results indicate that the accuracy of the correlations can be ranked in the following order: group contribution > curve fits > corresponding states. The success of the group contribution approach can be attributed to the structural information that is incorporated into the correlation. Using the group contribution method, one can estimate liquid heat capacities of the narrow-boiling range distillates with an overall accuracy of 8% using data from only 1H n.m.r. and elemental analysis.

Heat capacities and enthalpies of fusion of dibenzothiophene (220 to 560 K) and of biphenyl, cyclohexylbenzene, and cyclohexylcyclohexane (220 to 475 K) Enthalpies and temperatures of three transitions in solid cyclohexylcyclohexane

Heat capacities and enthalpies of transition have been measured by d.s.c. for dibenzothiophene (220 to 560 K) and biphenyl, cyclohexylbenzene, and cyclohexylcyclohexane (220 to 475 K). The measurements are considered accurate to ± 1.5 per cent for heat capacity and ± 1 to 2 per cent for enthalpies of fusion. Temperatures and enthalpies of fusion for the first three compounds are: dibenzothiophene, (371.0±0.5) K, (21.6±0.2) kJ·mol −1; biphenyl (342.2±0.5) K, (18.6±0.2) kJ·mol −1; and cyclohexylbenzene, (280.5±0.5) K, (15.3±0.2) kJ·mol −1. For cyclohexylcyclohexane, in addition to fusion, three solid-to-solid phase transitions were examined, at least one of which is hitherto unreported. Two of these are first-order transitions, and one appears to be of higher order, although the previous literature does not agree on this point. The temperatures and enthalpies obtained in the present work for these transitions are: S III = S IIb, (256.1±0.5) K, (1540±60) J·mol −1; S IIb = S IIa (higher order), (267.5±1.0) K (peak maximum), (740±40) J·mol −1 (from an arbitrary baseline); S IIa = S I, (273.5±0.5) K, (7080±150) J·mol −1; S I = L, (277.2±0.5) K, (6780±120) J·mol −1. The liquid-phase heat capacities of the three hydrocarbons are compared with values predicted from a group-additivity method, and reasonable agreement (1 to 4 per cent) is found over the temperature range intended for the predictions: 280 to 380 K. Above 380 K, however, deviations become significant for cyclohexylbenzene and cyclohexylcyclohexane, but not for biphenyl, suggesting that the aliphatic contributions in the estimation method need to be adjusted for application above 380 K.