Inorganic · H₂O
The universal process fluid and utility — cooling water, steam, and the reference for specific gravity. Cooling and heating utilities, steam systems, and as the density/viscosity reference for most calculations.
| Formula | H₂O |
| CAS number | 7732-18-5 |
| Synonyms | dihydrogen monoxide, H2O |
| Molar mass | 18.015 g/mol (Computed from the molecular formula and CODATA atomic weights) |
| Normal boiling point | 100 °C (NIST Chemistry WebBook (webbook.nist.gov)) |
| Liquid density | 997 kg/m³ (Reference liquid density near 20–25 °C (NIST WebBook)) |
Antoine equation (mmHg/°C): log₁₀(P) = 8.07131 − 1730.63 / (233.426 + T), valid 1–100 °C. Source: NIST Chemistry WebBook (webbook.nist.gov).
| °C | kPa | bar | mmHg | psia |
|---|---|---|---|---|
| 1.0 | 0.65 | 0.0065 | 4.9 | 0.094 |
| 20.8 | 2.45 | 0.0245 | 18.4 | 0.355 |
| 40.6 | 7.60 | 0.0760 | 57.0 | 1.102 |
| 60.4 | 20.24 | 0.2024 | 151.8 | 2.936 |
| 80.2 | 47.65 | 0.4765 | 357.4 | 6.911 |
| 100.0 | 101.34 | 1.0134 | 760.1 | 14.698 |
Using its Antoine constants (NIST Chemistry WebBook (webbook.nist.gov)), the saturation pressure of water at 25 °C is about 3.16 kPa. Use the calculator above for any temperature within 1–100 °C.
Water boils at 100 °C at atmospheric pressure (NIST Chemistry WebBook (webbook.nist.gov)). At that temperature its vapor pressure equals one atmosphere (760 mmHg).
Water (H₂O, CAS 7732-18-5) has a molar mass of 18.015 g/mol.