Title

Thermodynamic Properties Of Electrolytes In Methanol And Dimethylsulfoxide (volumes, Compressibilities, Heat Capacities, Calorimeters)

Date of Award

1985

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Abstract

Volumes, compressibilities, and heat capacities for univalent electrolytes and selected nonelectrolytes have been examined in methanol (MeOH) and dimethylsulfoxide (DMSO) at 25(DEGREES)C, and compared to water and other nonaqueous solvents. A high temperature flow calorimeter has been constructed which allowed study of heat capacities to 80(DEGREES)C.For alkali metal halides and tetraphenyl salts, (')V(,2)('0) and (')K(,s,2)('0) are strongly dependent upon solvent compressibilities. (')V(,2)('0) and (')K(,s,2)('0) become lower (less positive or more negative) as solvent compressibility increases in all of the solvents studied. (')V(,2)('0) becomes larger as ionic size increases. The change in (')K(,s,2)('0) with ionic size depends on solvent compressibility, (')K(,s,2)('0) becoming less negative in low compressibility solvents (water, DMSO), and more negative in high compressibility solvents (MeOH, EtOH, MeCN) as ionic size increases. (')V(,2)('0) and (')K(,s,2)('0) of simple electrolytes can be predicted with reasonable accuracy from solvent compressibilities and ionic sizes. (')V(,2)('0) and (')K(,s,2)('0) for tetraphenyl and tetraalykl ions involve additional factors. Solvent penetration is greater for tetraalkyl ions than for tetraphenyl ions. There is significant dissymmetry in (')V(,2)('0) and (')K(,s,2)('0) between(, )(phi)(,4)P('+) and (phi)(,4)B('-) in DMSO compared to MeOH. Tentative procedures to quantify this dissymmetry have been developed. A new thermodynamic function, the standard change in specific isentropic compressibility, ((DELTA)(beta)(,s)/m)('0), has been proposed as an additional tool for analyzing compressibilities.(')C(,p,2)('0) for alkali metal halides are positive and insensitive to temperature to 80(DEGREES)C in DMSO. In MeOH, (')C(,p,2)('0) for simple electrolytes are negative and decrease with temperature. This behavior in MeOH is attributed to strong electrostriction by ionic charge and bonding of anions to MeOH molecules, which increase with temperature, and result in large negative effects on heat capacity. Similar behavior occurs in water above 50-70(DEGREES)C. The charge effect on (')C(,p,2)('0) is positive and constant with temperature in DMSO, but becomes increasingly negative in MeOH and water. (')C(,p,2)('0) for benzene is positive in MeOH and DMSO, and increases with temperature, a reflection of the absence of ionic charge.

Keywords

Chemistry, Physical

Link to Full Text

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