Standard Thermodynamic Data
Standard enthalpies of formation (ΔHf°), Gibbs free energies of formation (ΔGf°), and standard molar entropies (S°) for common substances at 25°C and 1 atm.
| Substance | State | ΔHf° (kJ/mol) | ΔGf° (kJ/mol) | S° (J/mol·K) |
|---|---|---|---|---|
| H2 | g | 0 | 0 | 130.7 |
| O2 | g | 0 | 0 | 205.2 |
| N2 | g | 0 | 0 | 191.6 |
| C (graphite) | s | 0 | 0 | 5.7 |
| C (diamond) | s | 1.9 | 2.9 | 2.4 |
| H2O | l | -285.8 | -237.1 | 69.9 |
| H2O | g | -241.8 | -228.6 | 188.8 |
| CO2 | g | -393.5 | -394.4 | 213.8 |
| CO | g | -110.5 | -137.2 | 197.7 |
| CH4 | g | -74.6 | -50.5 | 186.3 |
| C2H6 | g | -84 | -32 | 229.2 |
| C2H2 | g | 227.4 | 209.9 | 200.9 |
| C6H6 | l | 49.1 | 124.5 | 173.4 |
| CH3OH | l | -238.4 | -166.6 | 126.8 |
| C2H5OH | l | -277.6 | -174.8 | 160.7 |
| NH3 | g | -45.9 | -16.4 | 192.8 |
| NO | g | 91.3 | 87.6 | 210.8 |
| NO2 | g | 33.2 | 51.3 | 240.1 |
| HCl | g | -92.3 | -95.3 | 186.9 |
| HF | g | -273.3 | -275.4 | 173.8 |
| SO2 | g | -296.8 | -300.1 | 248.2 |
| SO3 | g | -395.7 | -371.1 | 256.8 |
| NaCl | s | -411.2 | -384.1 | 72.1 |
| KCl | s | -436.5 | -408.5 | 82.6 |
| CaCO3 | s | -1206.9 | -1128.8 | 92.9 |
| Fe2O3 | s | -824.2 | -742.2 | 87.4 |
| Al2O3 | s | -1675.7 | -1582.3 | 50.9 |
| NaOH | s | -425.6 | -379.5 | 64.5 |
| AgCl | s | -127 | -109.8 | 96.3 |
| H2SO4 | l | -814 | -690 | 156.9 |
Important Notes
- All values at standard conditions: 25°C (298.15 K) and 1 atm (1 bar for gases).
- ΔHf° and ΔGf° for elements in their standard states are zero by definition.
- Use Hess's law: ΔH°rxn = Σ ΔHf°(products) − Σ ΔHf°(reactants).
- ΔG°rxn = Σ ΔGf°(products) − Σ ΔGf°(reactants). Negative ΔG° means the reaction is spontaneous at standard conditions.
- ΔG° = ΔH° − TΔS° relates enthalpy, entropy, and free energy.
- Entropy (S°) is always positive. Gases have higher S° than liquids, which have higher S° than solids.
- Data sourced from CRC Handbook of Chemistry and Physics and NIST Chemistry WebBook.