Properties of Hydrogen (H2)
Hydrogen is the lightest and most abundant chemical element in the universe. It is represented by the symbol “H” on the periodic table and has an atomic number of 1. Hydrogen is a colorless, odorless, and highly flammable gas in its natural state.
The following table provides a comprehensive list of hydrogen properties in both SI and US customary/Imperial units at normal temperature and pressure (NTP).
Click on the icon to switch between Metric and Imperial units.
| Physical Properties | Metric |
|---|---|
| Molar Mass | 2.016 g/mol |
| Density (0°C) | 0.0899 kg/m3 |
| Dynamic Viscosity (25°C) | 8.9 µPa·s |
| Speed of Sound in Gas (27°C) | 1320 m/s |
| Thermal Properties | Metric |
| Melting Point | -259.2 °C |
| Boiling Point | -252.9 °C |
| Thermal Conductivity (25°C) | 0.186 W/m·K |
| Specific Heat Capacity (Cp) | 14305 J/kg·K |
| Critical Constants | Metric |
| Critical Temperature (Tc) | -239.95 °C |
| Critical Pressure (Pc) | 1.298 MPa |
| Critical Density (ρc) | 30 kg/m3 |
| Electrical Properties | Metric |
| Relative Permittivity (εr) | 1.000264 |
| Optical Properties | Metric |
| Refractive Index (589 nm) | 1.000138 |
| Hazardous Data | Metric |
| Autoignition Temperature | 560 °C |
| Lower Flammability Limit | 4% |
| Upper Flammability Limit | 75% |
| NFPA Rating (Health) | 0 |
| NFPA Rating (Fire) | 4 |
| NFPA Rating (Reactivity) | 0 |
Unless stated otherwise, all values are taken at room temperature (approximately 20°C or 68°F) and 1 atm pressure. (1 atm = 101,325 Pa)
Related Pages
References: 1) Cardarelli, François. Materials Handbook: A Concise Desktop Reference. Switzerland: Springer International Publishing, 2018. 2) CRC Handbook of Chemistry and Physics, 97th Edition. United Kingdom: CRC Press, 2016-2017. 3) Yaws, Carl L. The Yaws Handbook of Physical Properties for Hydrocarbons and Chemicals. Netherlands: Elsevier Science, 2015. 4) Fire Protection Guide to Hazardous Materials, 14th Edition. United States: National Fire Protection Association, 2010.