Calorimetric determination of thermodynamic quantities for chemical reactions in the system CO2?NaOH?H2O from 225 to 325�C

Abstract

The phase equilibrium CO2(g)=CO2(aq) and the aqueous reactions CO32−+H+=HCO3−, HCO3−+H+=CO2(aq)+H2O, and Na++CO32−=NaCO3− were studied from 225 to 325°C using a flow calorimetric technique. Heats of mixing of gaseous CO2 with liquid H2O and with aqueous NaOH solutions were measured at these temperatures. Log K, ΔH, ΔS, and ΔCp values were determined for these reactions from the heat of mixing data. Equations for these thermodynamic quantities valid at infinite dilution (I=0) and 12.4 MPa are given as a function of temperature from 225 to 325°C. The log K and ΔH values agree well with literature values at these temperatures for the first and third reactions, but not for the second reaction. No previous results have been reported for the fourth reaction at high temperatures. The isocoulombic reaction principle is tested using the log K values determined in this study. This principle is found to be valid for the reactions where each charge on one side of the equation is balanced on the other side by a charge of the same sign and magnitude, but not for the reaction where two single negative charges (HCO3− and OH−) are balanced by one double negative charge (CO32−).