What is the NIST Chemistry WebBook?
The NIST Chemistry WebBook (webbook.nist.gov) is a free online database of chemical and physical data compiled and distributed by the National Institute of Standards and Technology (NIST) under its Standard Reference Data Program. It is designated SRD 69. You can use it to look up thermochemical, thermophysical, spectral, and ion energetics data for specific compounds, searching by name, chemical formula, CAS registry number, molecular weight, chemical structure, or selected ion energetics and spectral properties.
Who runs it and what it is
The site is maintained by NIST, a U.S. federal agency, and its contents are part of the NIST Standard Reference Data Program. NIST states that it uses its best efforts to deliver a high-quality copy of the database and to verify that the data were selected on the basis of sound scientific judgment, but it makes no warranties to that effect and is not liable for damage resulting from errors or omissions.
One thing to note for planning purposes: NIST reserves the right to charge for access to this database in the future. As described on the site, access is currently provided without a stated fee, but that could change.
What data it contains
The WebBook covers several distinct categories. The table below summarizes the main ones and their approximate scope as stated on the site.
| Data category | Approximate coverage | Examples of values |
|---|---|---|
| Thermochemical data | Over 7,000 organic and small inorganic compounds | Enthalpy of formation, enthalpy of combustion, heat capacity, entropy, phase transition enthalpies and temperatures, vapor pressure |
| Reaction thermochemistry | Over 8,000 reactions | Enthalpy of reaction, free energy of reaction |
| IR spectra | Over 16,000 compounds | Infrared spectra |
| Mass spectra | Over 33,000 compounds | Mass spectra |
| UV/Vis spectra | Over 1,600 compounds | Ultraviolet/visible spectra |
| Gas chromatography | Over 27,000 compounds | GC data |
| Electronic and vibrational spectra | Over 5,000 compounds | Electronic and vibrational spectra |
| Constants of diatomic molecules | Over 600 compounds | Spectroscopic data |
| Ion energetics | Over 16,000 compounds | Ionization energy, appearance energy, electron affinity, proton affinity, gas basicity, cluster ion binding energies |
| Thermophysical properties | 74 fluids | Density, specific volume, Cp, Cv, enthalpy, internal energy, entropy, viscosity, thermal conductivity, Joule-Thomson coefficient, surface tension (saturation curve only), sound speed |
How to search it
The site supports several search entry points for a specific compound:
- Name
- Chemical formula
- CAS registry number
- Molecular weight
- Chemical structure
- Selected ion energetics and spectral properties
This means you can start from whatever identifier you already have. If you only know a spectrum or an ion energetics value, the last option lets you search on that basis rather than requiring a name or CAS number.
When it is useful, and its limits
The WebBook is a reasonable first stop when you need a reference value for a known compound — for example, a formation enthalpy, a mass spectrum, or the viscosity of one of the 74 covered fluids. Because the data are compiled under a national standards program, they are commonly cited in academic and technical work.
Keep the following in mind:
- Coverage is broad but not universal. The counts above are the site's own figures, and a compound outside those sets may not appear.
- The thermophysical property data cover 74 fluids specifically, not all substances.
- Surface tension is given only along the saturation curve.
- NIST explicitly disclaims warranties, so verify critical values against primary sources when the stakes are high.
- Access terms could change, since NIST reserves the right to charge in the future.
If your compound is in scope and you need a standard reference value, the WebBook is a direct and citable source. If you need data outside these categories, or for a substance not covered, you will need another database.