K.N. Marsh

An isothermal displacement calorimeter for endothermic enthalpies of mixing

Abstract 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.

A continuous dilution dilatometer the excess volume for the system cyclohexane + benzene☆

Abstract An apparatus for the direct measurement of the excess volumes of mixing for a binary system by continuous dilution is described. The excess volume for the system cyclohexane + benzene at 25° C has been measured and comparison is made with previous determinations. The apparatus is capable of a precision of ±0.0005 cm3 mol−1 in the excess volume.

Excess volumes for alcohols + non-polar solvents I. Ethanol + cyclohexane, + n-hexane, + benzene, + carbon tetrachloride, + cyclopentane, and + p-xylene

Abstract A dilution dilatometer for determining excess volumes at high dilutions of ethanol in the range x (C 2 H 5 OH) ≈ 1 × 10 −3 to ≈8 × 10 −2 , is described. Excess volumes for ethanol +cyclohexane, + n -hexane, +benzene, +carbon tetrachloride, +cyclopentane, and + p -xylene are reported at temperatures from 283.15 to 318.15 K. The excess volumes are highly unsymmetrical, with the function V E x(1−x) showing a very rapid increase at low mole fractions of ethanol. The limiting partial molar excess volumes of ethanol in the various non-polar solvents show a similar trend to that observed for the limiting partial molar excess enthalpy of ethanol in the same solvents.

Enthalpies of mixing of n-hexane + cyclohexane at 25 °C

Abstract The enthalpy of mixing of n-hexane+cyclohexane has been measured at 25 °C as a contribution to the establishment of reliable values for use in testing enthalpy-of-mixing calorimeters.

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

Abstract 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 cm3 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.

A general method for calculating the excess Gibbs free energy from isothermal vapour-liquid equilibria

Abstract A general equation is proposed for calculating excess Gibbs free energies from isothermal vapour-liquid equilibria and the relation between this equation and various other equations is established. The proposed equation appears satisfactory for representing the excess functions of highly unsymmetrical polar + non-polar mixtures.

The isothermal displacement calorimeter: design refinements

Abstract 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.

A stepwise dilution technique for measuring the static dielectric properties of liquid mixtures Dielectric behaviour of ethanol in cyclohexane, n-hexane, carbon tetrachloride, benzene, p-xylene, and carbon disulphide

Dielectric constants at audio-frequency have been measured for solutions of ethanol in various non-polar solvents in the range x(C2H5OH) ≈ 6 × 10−4 to 0.2 using a stepwise dilution technique. The mixtures studied are: ethanol + cyclohexane at 283.15, 298.15, and 318.15 K; ethanol + n-hexane, +benzene, +carbon tetrachloride, +p-xylene, and +carbon disulphide at 298.15 K. The results are analysed in terms of a number of theories to obtain the apparent dipole moment as a function of mole fraction. This quantity varies considerably with both the solvent and the mole fraction. It is concluded that the aromatic solvents and carbon tetrachloride interact with the free OH groups on the monomeric alcohol and terminal OH groups of linear hydrogen-bonded chains. This has the effects that (a) the absolute amounts of the hydrogen-bonded species are lower in these solvents than at the same total mole fraction of alcohol in n-hexane, cyclohexane, or carbon disulphide, and (b) the ratio of cyclic to linear associated forms is lower in the aromatic solvents and carbon tetrachloride than in the other solvents. These effects account qualitatively for the great difference in the apparent dipole moment observed in various solvents.

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

Abstract 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.

Activity coefficients in the ternary system: water + sucrose + sodium chloride

Abstract Isopiestic vapour pressure measurements on mixed solutions of sucrose and sodium chloride at molalities up to 6 mol kg −1 with respect to each solute at 25 °C are reported and used to evaluate the activity coefficients of the solutes. The correctness of the results is confirmed by calculations of the solubilities, which compare well with experimental literature values.