Enthalpy of combustion of acetylsalicylic acid

Abstract

The massic energy of combustion of crystalline acetylsalicylic acid was determined in an NIST adiabatic-aneroid-rotation bomb calorimeter. The standard molar enthalpy of combustion at T = 298.15 K and p o = 10 5Pa is Δ c H m o (C 9H 8O 4, cr, 298.15K) = − (3926.71 ± 0.34)kJ · mol − 1 . The derived standard molar enthalpy of formation is Δ f H m o (C 9H 8O 4, cr, 298.15K) = − (758.19 ± 0.52) kJ · mol − 1 . The molar enthalpy of fusion Δ fus H m o (C 9H 8O 4, cr, 414.0K) = (29.80 ± 0.22)kJ · mol − 1 was determined by differential scanning calorimetry. The molar Kirchhoff relationship, d( ΔH) = ΔC p d T, was used to convert this value to T = 298.15 K, Δ fus H m o (C 9H 8O 4, cr, 298.15K) = (19.28 ± 0.22)kJ · mol − 1 . The molar enthalpy of vaporization was estimated using the group contribution scheme of Lebedev and Miroshnichenko. The molar enthalpy of vaporization of acetylsalicyclic acid was estimated as Δ vap H m o (C 9H 8O 4, cr, 298.15K) = (106.4 ± 2.0)kJ · mol − 1 . The molar enthalpies of fusion and vaporization were used to calculate enthalpies of formation for the liquid and gaseous states of acetylsalicyclic acid, Δ f H m o (C 9H 8O 4, l, 298.15K) = − (738.91 ± 0.56)kJ · mol − 1 and Δ f H m o (C 9H 8O 4, g, 298.15K) = − (632.5 ± 2.1)kJ · mol − 1 , respectively.