Isothermal Displacement Calorimeter Research Articles

Excess functions for cyclopentane+cyclohexane, cyclopentane+cycloheptane, and cyclohexane+cyclo-octane

Excess enthalpies for cyclopentane+cycloheptane at 288.15, 298.15, and 308.15 K and excess enthalpies for cyclohexane+cyclo-octane at 288.15, 298.15, 308.15, and 318.15 K have been measured with an isothermal displacement calorimeter. The excess volumes for cyclopentane+cyclohexane and cyclopentane+cycloheptane have been measured over a similar temperature range, using a dilution dilatometer. Vapour pressures for cyclopentane+cyclohexane, cyclopentane+cycloheptane, and cyclohexane+cyclo-cotane have been measured at 298.15 K by a precise static technique. The excess Gibbs free energies for the three mixtures have been calculated over the temperature range from the vapour pressures and the temperature dependence of the excess enthalpies. Isothermal compressibilities for cyclopentane+cyclohexane and cyclohexane+cyclo-octane have been measured at 298.15 K.

Molar excess enthalpies and volumes of isomeric dichloroethylene mixtures at 298.15 K

Excess molar enthalpies and volumes for the three binary mixtures of cis-dichloroethylene, trans-dichloroethylene, and carbon tetrachloride were measured at 298.15 K with an isothermal displacement calorimeter and a double-stem pyknometer. The results are qualitatively interpreted in terms of dispersion and dipolar interactions.

Excess Gibbs free energies, excess enthalpies, and excess volumes for 2,3-dimethylbutane+ cyclo-octane

The excess enthalpies of mixtures of 2,3-dimethylbutane+cyclo-octane have been measured at 288.15, 298.15, and 313.15 K with an isothermal displacement calorimeter. The excess volumes have been measured at the same temperatures with a dilution dilatometer. Vapour pressures of the mixtures have been measured at 298.15 K by a precise static vapour pressure technique. The excess Gibbs free energy, calculated at the three temperatures from the vapour pressure measurements and the temperature dependence of the excess enthalpies has a maximum of 184 J mol−1. The excess Gibbs free energy is independent of temperature, within experimental error, over the temperature range considered. The excess enthalpy has a maximum of 185 J mol−1 at 288.15 K. The enthalpies decrease with increase in temperature. The excess volume has a minimum of −0.63 cm3 mol−1 at 288.15 K and the volumes become more negative with increase in temperature. All the extrema are at a mole fraction of cyclo-octane of 0.47.

Excess Gibbs free energies, excess enthalpies, and excess volumes for mixtures of cyclopentane+2,3-dimethylbutane

The excess enthalpies of cyclopentane+2,3-dimethylbutane have been measured at 288.15, 298.15, and 308.15 K, with an isothermal-displacement calorimeter. The excess volumes have been measured at the same temperatures with a dilution dilatometer. Vapour pressures of the mixtures have been measured at 298.15 K by a precision static vapour pressure technique. The excess Gibbs free energy, calculated at the three temperatures from the vapour pressure measurements and the temperature dependence of the excess enthalpies, is independent of temperature and has a maximum of 12 J mol −1 . At 298.15 K the excess enthalpy changes sign with composition and becomes more positive with increase in temperature. The excess volumes are independent of temperature and have a minimum of −0.268 cm 3 mol −1 .

Enthalpies of dilution of urea solutions in six polar solvents at several temperatures

Using the isothermal displacement calorimeter, enthalpies of dilution are obtained for solutions of urea in water, methanol, ethanol, formamide, N,N-dimethyl-formamide, and dimethyl sulfoxide. The results are discussed in terms of solute-solvent and solute-solute interactions.

An Isothermal Displacement Calorimeter for Measuring Enthalpies of Mixing

Abstract An isothermal displacement calorimeter of the Van Ness type has been constructed. The calorimeter was tested on three systems, benzene+cyclohexane, cyclohexane+n-hexane, and benzene+dichloromethane, at 25°C, and the performance of the calorimeter was discussed in connection with the literature values. The precision of the new calorimeter was within 0.5%; this was equal to, or better than, that of calorimeters of a similar type which have been constructed by several investigators.

The isothermal displacement calorimeter: design refinements

The isothermal displacement calorimeter described in previous publications has been modified and rebuilt. Further constructional details are given and results for the systems cyclohexane + n-hexane and benzene + cyclohexane, both at 25 °C, are compared with the results from earlier models.

Excess enthalpies, excess volumes, and excess gibbs free energies for mixtures of cyclo-octane+cyclopentane at 288.15, 298.15, and 308.15 K

The excess volumes for the system cyclo-octane + cyclopentane have been measured at 288.15, 298.15, and 308.15 K with a dilution dilatometer. The excess volume has a minimum of −0.25 cm 3 mol −1 at 288.15 K and becomes more negative with increase in temperature. Vapour pressures of the mixtures have been measured at the same temperatures by a precision static vapour pressure technique. The derived excess Gibbs free energy changes sign with composition and becomes more negative with increase in temperature. Excess enthalpies have been measured at 288.25 and 308.32 K with an isothermal displacement calorimeter. Measurements at 298.15 K have been presented previously. The excess enthalpy has a minimum of −33.7 J mol −1 at 288.25 K and becomes more negative with increase in temperature. Enthalpies calculated from the temperature dependence of the excess Gibbs free energy are consistent, within experimental error, with the direct measurements.

Enthalpies of mixing and excess Gibbs free energies of mixtures of octamethylcyclotetrasiloxane+cyclopentane at 291.15, 298.15, and 308.15 K

The enthalpies of mixing of octamethylcyclotetrasiloxane+cyclopentane have been measured at 291.15, 298.15, and 308.15 K with an isothermal displacement calorimeter. Vapour pressures of the mixtures have been measured at the same temperatures by a precision static vapour pressure method. The enthalpy of mixing has a maximum of 227 J mol −1 at 291.15 K and the enthalpies decrease with increase in temperature. The excess Gibbs free energy, calculated from the vapour pressures, has a minimum of −199 J mol −1 at 291.15 K. This function becomes more negative with increase in temperature. The excess volumes, measured previously, change sign with composition and are independent of temperature.

Excess enthalpies of octamethylcyclotetrasiloxane mixtures

Excess enthalpies and partial molar excess enthalpies for the systems octamethylcyclotetrasiloxane + benzene and octamethylcyclotetrasiloxane + carbon tetrachloride have been measured at 25 and 45°C with an isothermal displacement calorimeter. For the first system the directly measured partial molar excess enthalpies of benzene agree, within experimental limits, with those determined from vapour pressure measurements. The measured excess enthalpies have a precision of ±2 J mol–1 for the benzene solutions and ±0.3 J mol–1 for the carbon tetrachloride solutions.

Enthalpies of exothermic mixing measured by the isothermal displacement calorimeter for cyclo-octane + cyclopentane at 25 °C

The isothermal displacement calorimeter previously described is readily adapted to the measurement of exothermic enthalpies of mixing. Results for cyclo-octane + cyclopentane are given.

An isothermal displacement calorimeter for endothermic enthalpies of mixing

An isothermal displacement calorimeter has been constructed and used to measure the enthalpies of mixing for the systems benzene+cyclohexane at 25 °C and benzene+carbon tetrachloride at 25 °C. Detailed comparisons with previous measurements are made. The calorimeter has the advantage that partial molar enthalpies of mixing of the added component are measured directly. Its precision appears to be higher than that of previous instruments.