Enthalpy of solution of oxalic, succinic, adipic, maleic, malic, tartaric, and citric acids, oxalic acid dihydrate, and citric acid monohydrate in water at 298.15 K

Enthalpies of solution of several organic acids in water at 298.15 K were measured in an LKB calorimeter. The molar enthalpies of solution extrapolated to infinite dilution are for anhydrous oxalic acid, Δ_solH_m^∞(298.15 K) = (8853 ± 99) J · mol^-1 and for oxalic acid dihydrate, Δ_solH_m^∞(298.15 K) = (35225 ± 72) J · mol^-1. The molar enthalpies of solution for finite molalities are: anhydrous citric acid, Δ_solH_m(298.15 K, m = 0.0200 mol · kg^-1) = (18211 ± 69) J · mol^-1; citric acid monohydrate, Δ_solH_m(298.15 K, m = 0.0203 mol · kg^-1) = (29061 ± 123) J · mol^-1; succinic acid, Δ_solH_m(298.15 K, m = 0.0334 mol · kg^-1) = (28705 ± 89) J · mol^-1; adipic acid, Δ_solH_m(298.15 K, m = 0.0195 mol · kg^-1) = (32848 ± 82) J · mol^-1; maleic acid, Δ_solH_m(298.15 K, m = 0.0256 mol · kg^-1) = (21333 ± 29) J · mol^-1; malic acid, Δ_solH_m(298.15 K, m = 0.0318 mol · kg^-1) = (21846 ± 86) J · mol^-1; and tartaric acid, Δ_solH_m(298.15 K, m = 0.0310 mol · kg^-1) = (15705 ± 29) J · mol^-1. The molar enthalpies of hydration are for oxalic acid, Δ_hydrH_m(298.15 K) = -(26.34 ± 0.17) kJ · mol^-1; and for citric acid, Δ_hydrH_m(298.15 K) = -(10.85 ± 0.19) kJ · mol^-1.