The effect of the molecular shape on the enthalpic behaviour of liquid mixtures: cyclic hydrocarbons in heptane and tetrachloromethane

Excess enthalpies HE at 298.15 K have been determined by flow microcalorimetry for binary mixtures of heptane or tetrachloromethane + a cyclic hydrocarbon (cycloheptane, cyclooctane, cyclodecane, 1,2,3,4-tetrahydronaphthalene, cis-decahydronaphthalene, trans-decahydronaphthalene, bicyclohexyl). With the exception of tetrahydronaphthalene + tetrachloromethane and of trans-decahydronaphtalene + heptane, all mixtures examined exhibit positive deviations. HEs have been analysed in terms of the DISQUAC model. Partial molar excess enthalpies at infinite dilution as well as standard enthalpies of solvation, ΔHo, have been evaluated for cycloalkanes in the two solvents and compared with those of linear and branched alkanes. The effect of cyclization upon ΔHo has been discussed and the contributions to ΔHo of the cavity and of the interaction terms have been estimated through the scaled particle theory.