Beiping Liu

Heat capacities and thermodynamic functions of p-chlorobenzoic acid

The heat capacities of p-chlorobenzoic acid were measured in the temperature range from 80 to 580 K by means of an automatic adiabatic calorimeter equipped with a small sample cell of internal volume of 7.4cm(3). The construction and procedures of the calorimetric system were described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on alpha-Al2O3. The deviations of experimental heat capacities from the corresponding smoothed values lie within +/-0.28 per cent, while the inaccuracy is within +/-0.40 per cent, compared with the recommended reference data in the whole experimental temperature range. A fusion transition at T = 512.280 K was found from the C-p-T curve of p-chlorobenzoic acid. The enthalpy and entropy of the phase transition, as well as the thermodynamic functions {G((T)) - G((298.15))}, {H-(T) - H-(298.15)} and {S-(T) - S-298.15}, were derived from the heat capacity data. The mass fraction purity of p-chlorobenzoic acid sample used in the present calorimetric study was determined to be 0.99935 by fraction melting approach

Calorimetric study and thermal analysis of [ErY(Ala)4(H2O)8](ClO4)6 (Ala=ALANINE)

A solid complex of rare-earth compounds with alanine, [ErY(Ala)4(H2O)8](ClO4)6 (Ala=alanine), was synthesized, and a calorimetric study and thermal analysis for it was performed through adiabatic calorimetry and thermogravimetry. The low-temperature heat capacity of [ErY(Ala)4(H2O)8](ClO4)6 was measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 K. A solid-solid phase transition was found between 99 and 121 K with a peak temperature at 115.78 k. The enthalpy and entropy of the phase transition was determined to be 1.957 Kj mol-1, 16.90 j mol-1 k-1, respectively. Thermal decomposition of the complex was investigated in the temperature range of 40~550°C by use of the thermogravimetric and differential thermogravimetric (TG/DTG) analysis techniques. The TG/DTG curves showed that the decomposition started from 120 and ended at 430°C, completed in three steps. A possible mechanism of the thermal decomposition was elucidated.

Low-temperature heat capacity and thermodynamic properties of [Re2(Ile)4(H2O)8](ClO4)6 (Re=Nd, Er, Ile=isoleucine)

AbstractThe heat capacities of two kinds of rare-earth element solid complexes with isoleucine [Re 2 (Ile) 4 (H 2 O) 8 ](ClO 4 ) 6 (whereRe = Nd, Er, and Ile = isoleucine) have been measured by an automatic adiabatic calorimeter in the temperature rangefrom 80 to 370K. Two solid–solid phase transitions were found from the C p curve of Nd formed complex in the rangeof 165–175K with a peak temperature of 167.88K and in the range of 195–210K with a peak temperature of 202.13K.The corresponding molar enthalpies of these phase transitions were determined to be 404.61Jmol −1 and 2.955kJmol ,respectively. One solid–solid phase transition was found for the Er formed complex in the range of 190–205K with a peaktemperature of 193.42K. The corresponding molar enthalpy of this transition was 14.11kJmol −1 . Smooth heat capacities andthermodynamic functions relative to the standard state (298.15K), H T − H 298 . 15 , S T − S 298 . 15 and −[ G T − G 298 . 15 ], of thetwo compounds, were calculated on basis of experimental heat capacity data. Possible mechanisms of thermal decompositionsfor the pair of compounds were suggested according to the thermogravimetric (TG) analysis.© 2002 Elsevier Science B.V. All rights reserved.

Calorimetric study and thermal analysis of [Ho-2(Ala)(4)(H2O)(8)]Cl-6 and [ErY(Ala)(4)(H2O)(8)] (ClO4)(6)

Two solid complexes of rare-earth compounds with alanine, [ho2(ala)(4)(h2o)(8)] cl-6 and [ery(ala)(4)(h2o)(8)] (clo4)(6) (ala = alanine) were synthesized, and a calorimetric study and thermal analysis for the two complexes were performed through adiabatic calorimetry and thermogravimetry. the low-temperature heat capacities of [ho2(ala)(4)(h2o)(8)] cl-6 and [ery(ala)(4)(h2o)(8)] (clo4)(6) were measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 k. solid-solid phase transitions were found between 214 k and 255 k with a peak temperature of 235.09 k for [ho2(ala)(4)(h2o)(8)] cl-6, between 99 k and 121 k with a peak temperature of 115. 78 k for [ery (ala)(4) (h2o)(8)] (clo4)(6). the enthalpies and entropies of the phase transitions were determined to be 3.02 kj . mol(-1), 12.83 j . k-1 . mol(-1) for [ho2(ala)(4)(h2o)(8)] cl-6; 1.96 kj . mol(-1), 16.90 j . k-1 . mol(-1) for [ery(ala)(4)(h2o)(8)] (clo4)(6), respectively. thermal decomposition of the two complexes were investigated in the temperature range of 40 similar to 800 degreesc by using the thermogravimetric and differential thermogravimetric (tg/dtg) analysis techniques. the tg/dtg curves showed that the decomposition started from 80 degreesc and ended at 479 degreesc, completed in two steps for [ho2 (ala)(4) (h2o)(8)]cl-6, and started from 120 degreesc and ended at 430 degreesc, completed in three steps for [ery(ala)(4) (h2o)(8)] (clo4)(6), respectively. the possible mechanisms of the thermal decompositions were elucidated.