The enthalpies of solution and formation of ammonia

Abstract The standard enthalpy of solution of gaseous ammonia in water to form the non-ionized solute was found to be ΔHsolno(298.15 K) = − (8448 ± 15) calth mol−1 by direct solution calorimetry. The results were compared with values from other sources, and the value So(NH4+, aq, 298.15 K) = (26.45 ± 0.13) calth K−1 mol−1 was calculated from adjuvant data on the solution and ionization processes. The enthalpy of formation of NH3(g) was recalculated from a third-law analysis of measurements on the equilibrium: 2 3 H 2 (g) + 1 2 N 2 (g) = NH 3 (g) . A set of best values for some of the thermodynamic properties of the ammonia species is suggested.

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