These are molar heats of formation for anions and cations in aqueous solution. In all cases, the heats of formation are given in kJ/mol at 25°C for 1 mole of the ion.

Cations ΔHf (kJ/mol) Anions ΔHf (kJ/mol)
Ag+ (aq) +105.9 Br- (aq) -120.9
Al3+ (aq) -524.7 Cl- (aq) -167.4
Ba2+ (aq) -538.4 ClO3- (aq) -98.3
Ca2+ (aq) -543.0 ClO4- (aq) -131.4
Cd2+ (aq) -72.4 CO32- (aq) -676.3
Cu2+ (aq) +64.4 CrO42- (aq) -863.2
Fe2+ (aq) -87.9 F- (aq) -329.1
Fe3+ (aq) -47.7 HCO3- (aq) -691.1
H+ (aq) 0.0 H2PO4- (aq) -1302.5
K+ (aq) -251.2 HPO42- (aq) -1298.7
Li+ (aq) -278.5 I- (aq) -55.9
Mg2+ (aq) -462.0 MnO4- (aq) -518.4
Mn2+ (aq) -218.8 NO3- (aq) -206.6
Na+ (aq) -239.7 OH- (aq) -229.9
NH4+ (aq) -132.8 PO43- (aq) -1284.1
Ni2+ (aq) -64.0 S2- (aq) +41.8
Pb2+ (aq) +1.6 SO42- (aq) -907.5
Sn2+ (aq) -10.0
Zn2+ (aq) -152.4
Reference: Masterton, Slowinski, Stanitski, Chemical Principles, CBS College Publishing, 1983.