The molar heat of formation of a compound (ΔHf) is equal to its enthalpy change (ΔH) when one mole of compound is formed at 25°C and 1 atm from elements in their stable form. This is a table of the heats of formation for a variety of common compounds. As you can see, most heats of formation are negative quantities, which implies that the formation of a compound from its elements usually is an exothermic process. | Compound | ΔHf (kJ/mol) | Compound | ΔHf (kJ/mol) |
| AgBr(s) | -99.5 | C2H2(g) | +226.7 |
| AgCl(s) | -127.0 | C2H4(g) | +52.3 |
| AgI(s) | -62.4 | C2H6(g) | -84.7 |
| Ag2O(s) | -30.6 | C3H8(g) | -103.8 |
| Ag2S(s) | -31.8 | n-C4H10(g) | -124.7 |
| Al2O3(s) | -1669.8 | n-C5H12(l) | -173.1 |
| BaCl2(s) | -860.1 | C2H5OH(l) | -277.6 |
| BaCO3(s) | -1218.8 | CoO(s) | -239.3 |
| BaO(s) | -558.1 | Cr2O3(s) | -1128.4 |
| BaSO4(s) | -1465.2 | CuO(s) | -155.2 |
| CaCl2(s) | -795.0 | Cu2O(s) | -166.7 |
| CaCO3 | -1207.0 | CuS(s) | -48.5 |
| CaO(s) | -635.5 | CuSO4(s) | -769.9 |
| Ca(OH)2(s) | -986.6 | Fe2O3(s) | -822.2 |
| CaSO4(s) | -1432.7 | Fe3O4(s) | -1120.9 |
| CCl4(l) | -139.5 | HBr(g) | -36.2 |
| CH4(g) | -74.8 | HCl(g) | -92.3 |
| CHCl3(l) | -131.8 | HF(g) | -268.6 |
| CH3OH(l) | -238.6 | HI(g) | +25.9 |
| CO(g) | -110.5 | HNO3(l) | -173.2 |
| CO2(g) | -393.5 | H2O(g) | -241.8 |
| H2O(l) | -285.8 | NH4Cl(s) | -315.4 |
| H2O2(l) | -187.6 | NH4NO3(s) | -365.1 |
| H2S(g) | -20.1 | NO(g) | +90.4 |
| H2SO4(l) | -811.3 | NO2(g) | +33.9 |
| HgO(s) | -90.7 | NiO(s) | -244.3 |
| HgS(s) | -58.2 | PbBr2(s) | -277.0 |
| KBr(s) | -392.2 | PbCl2(s) | -359.2 |
| KCl(s) | -435.9 | PbO(s) | -217.9 |
| KClO3(s) | -391.4 | PbO2(s) | -276.6 |
| KF(s) | -562.6 | Pb3O4(s) | -734.7 |
| MgCl2(s) | -641.8 | PCl3(g) | -306.4 |
| MgCO3(s) | -1113 | PCl5(g) | -398.9 |
| MgO(s) | -601.8 | SiO2(s) | -859.4 |
| Mg(OH)2(s) | -924.7 | SnCl2(s) | -349.8 |
| MgSO4(s) | -1278.2 | SnCl4(l) | -545.2 |
| MnO(s) | -384.9 | SnO(s) | -286.2 |
| MnO2(s) | -519.7 | SnO2(s) | -580.7 |
| NaCl(s) | -411.0 | SO2(g) | -296.1 |
| NaF(s) | -569.0 | So3(g) | -395.2 |
| NaOH(s) | -426.7 | ZnO(s) | -348.0 |
| NH3(g) | -46.2 | ZnS(s) | -202.9 |
Reference: Masterton, Slowinski, Stanitski, Chemical Principles, CBS College Publishing, 1983.
