Heats of Formation Table

Enthalpy of Cations and Anions in Aqueous Solution

Use heat of formation to tell whether energy is absorbed or released in a reaction.
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Anne Marie Helmenstine, Ph.D.
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  • Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
  • B.A., Physics and Mathematics, Hastings College
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
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Anne Marie Helmenstine, Ph.D.
Updated November 04, 2019

The molar heat of formation or standard enthalpy of formation is the change in enthalpy when 1 mole of a substance is formed from its elements under standard state conditions. The standard enthalpy change of formation is the sum of the heats of formation of the products of a reaction minus the sum of the heats of formation of the reactants.

Molar Heat of Formation

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.