Thermodynamics for ionization of water at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa: apparent molar volumes of aqueous KCl, KOH, and NaOH and apparent molar heat capacities of aqueous HCl, KCl, KOH, and NaOH

摘要

Apparent molar volumes V_#phi# of aqueous KCl, KOH, and NaOH and apparent molar heat capacities C_p,#phi# of aqueous HCl, KCl, KOH, and NaOH have been determined at the pressure p = 0.35 MPa, and at molalities 0.015 < = m/mol·kg~(_1) < = 0.5. Densities were measured using a vibrating-tube densimeter (DMA 512, Anton Paar, Austria) at temperatures 278.15 < = T/K < = 368.15. These values were used to calculate the apparent molar volumes. A fixed-cell, differential-output, power-compensating, temperature-scanning calorimeter (NanoDSC model 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.) was used to measure the heat capacities of the same solutions at temperatures 278.15 < = T/K < = 393.15. Results were fitted by using equations that describe the surfaces (m, T, V_#phi#) and (m, T, C_p,#phi#). Using these equations, we have calculated the surfaces (m, T, #DELTA#_rV_m), (m, T, #DELTA#_rC_p,m),(m, T, #DELTA#_rH_m),(m, T, pQ_a), and (m, T, #DELTA#_rS_m) for the ionization of water in the presence of combinations of the above electrolytes. The last three surfaces were calculated by integration using our (m, T, #DELTA#_rC_p,m) surface and literature values for the molality dependence of #DELTA#_rH_m and pQ_a at T = 298.15K.