The isothermal displacement calorimeter: Design modifications for measuring exothermic enthalpies of mixing

Abstract

The isothermal displacement calorimeter described previously has been modified by the inclusion of a thermoelectric cooling module to allow the study of both endothermic and exothermic mixing. Other modifications are also described. Excess enthalpies are reported for 1,4-dioxan+tetrachloro-methane, benzene+dichloromethane, tetrahydrofuran+water, and ethanol+water at 298.15 K and 1,4- dioxan+dichloromethane at 298.15 and 303.15 K. These mixtures have been suggested as possible reference mixtures for either checking the operation of, or calibrating, calorimeters to be used for making measurements on exothermic mixtures. The performances of our calorimeters have been evaluated on the basis of the results presented here and by comparison with previous results. Some advantages and disadvantages of the proposed reference mixtures are discussed. Photochemical effects from the tungsten thermostat lamp affect the results for mixtures of tetra-chloromethane with 1,4-dioxan.

Relative Effects of Alcohol and pH on Betacyanin Stability in Aqueous Djulis Extracts and Their Color Qualities after Organic Acid Addition

“…The observation above reported two competing factors: ethanol-water mixing and ethanol-betacyanin interaction. The latter effect results in color degradation and the former might buffer the ethanol effects on color degradation and lead to a minimum near the molar ratio of ethanol at which the largest heat of mixing or most exothermic ethanolwater mixture occurs (Costigan et al 1980).…”

Hydrogen bond network relaxation resolved by alcohol hydration (methanol, ethanol, and glycerol)

“…a–c), which is likely due to the polarization through nonbonding electrons. The softening of H–O bond explains why mixing alcohols with water is exothermic and the mixture has lower melting temperatures, while the polarization‐induced softening of O:H segment contributes the observed depression of freezing temperatures …”

Experimental study and ERAS modeling of the excess molar enthalpy of (acetonitrile+1-heptanol or 1-octanol) mixtures at (298.15, 313.15, and 323.15)K and atmospheric pressure

“…A comparison between experimental data with the plentiful literature data taken from Costigan et al [18] shows an average difference lower than 1.0% over the whole composition range.…”

“…The performance of the calorimeter was tested by measuring H E m of the well-investigated system (ethanol + water) [16][17][18] at 298.15 K over the whole composition range and atmospheric pressure. A comparison between experimental data with the plentiful literature data taken from Costigan et al [18] shows an average difference lower than 1.0% over the whole composition range.…”