Determination of Equilibrium Constants for Reactions between Nitric Oxide and Ammoniacal Cobalt(II) Solutions at Temperatures from 298.15 to 309.15 K and pH Values between 9.06 and 9.37 under Atmospheric Pressure in a Bubble Column

Experiments were conducted in a bubble column to determine the equilibrium constants of reactions between NO and ammoniacal cobalt­(II) solutions at temperatures between 298.15 and 310.15 K and pH values from 9.06 to 9.37 under atmospheric pressure. The two reactions are 2Co­(NH₃)₅(H₂O)²⁺ + 2NO ⇌ (NH₃)₅Co­(N₂O₂)­Co­(NH₃)₅⁴⁺ + 2H₂O and 2Co­(NH₃)₆²⁺ + 2NO ⇌ (NH₃)₅Co­(N₂O₂)­Co­(NH₃)₅⁴⁺ + 2NH₃, respectively. Their equilibrium constants are calculated on the fraction molar basis. All experimental data fit well to the equations ln K_NO⁵ = 3598.5­(1/T) + 16.759 and ln K_NO⁶ = 1476.4­(1/T) + 26.597, which give the enthalpy of reactions between NO and penta- and hexaamminecobalt­(II) nitrates: Δ_rH₅° = −29.92kJ·mol^–1 and Δ_rH₆° = −12.27kJ·mol^–1.