Properties of Common Gases
Molar mass, gas constant, density, viscosity and speed of sound of nine common gases at 20 C and 1 atm.
Different gases behave very differently: hydrogen is 14 times lighter than air and carries sound nearly four times as fast, while carbon dioxide is half again as heavy. This table compares nine common gases at 20 C and atmospheric pressure, with the density, the gas constant and the speed of sound worked out from the molar mass and the heat capacity ratio.
The table
| Gas | Molar mass (g/mol) | Gas constant R (J/kg K) | Density at 20 C, 1 atm (kg/m3) | Heat capacity ratio gamma | Specific heat cp (J/kg K) | Dynamic viscosity (micropascal seconds) | Kinematic viscosity (mm2/s) | Speed of sound (m/s) | Density compared with air |
|---|---|---|---|---|---|---|---|---|---|
| Air (dry) | 28.96 | 287.1 | 1.2039 | 1.4 | 1005 | 18.2 | 15.12 | 343 | 1 |
| Nitrogen | 28.013 | 296.8 | 1.1645 | 1.4 | 1039 | 17.6 | 15.11 | 349 | 0.967 |
| Oxygen | 31.999 | 259.8 | 1.3302 | 1.4 | 918 | 20.4 | 15.34 | 327 | 1.105 |
| Carbon dioxide | 44.01 | 188.9 | 1.8295 | 1.3 | 846 | 14.7 | 8.03 | 268 | 1.519 |
| Hydrogen | 2.016 | 4124.2 | 0.0838 | 1.41 | 14307 | 8.8 | 105 | 1306 | 0.07 |
| Helium | 4.0026 | 2077.3 | 0.1664 | 1.66 | 5193 | 19.6 | 117.79 | 1005 | 0.138 |
| Argon | 39.948 | 208.1 | 1.6607 | 1.67 | 520 | 22.3 | 13.43 | 319 | 1.379 |
| Methane | 16.043 | 518.3 | 0.6669 | 1.31 | 2254 | 11 | 16.49 | 446 | 0.554 |
| Propane | 44.097 | 188.5 | 1.8332 | 1.13 | 1670 | 8.1 | 4.42 | 250 | 1.522 |
Source and notes: Molar masses and typical gas properties at 20 C and 101.325 kPa (standard tables: Cengel and Ghajar, Appendix; CRC Handbook). Calculated: R = 8 314.46 / M, density = P / (R T), kinematic viscosity = dynamic viscosity / density, speed of sound = sqrt(gamma R T). Values for gamma and viscosity are typical and vary a little with temperature.
How to use this table
- Find the gas.
- Use the density for mass flow and buoyancy, the gas constant R in the ideal gas law (P = ρ R T), and the speed of sound for Mach number and choked flow.
- For another temperature or pressure, scale the density with P ÷ T.
Worked example: lifting power of helium and hydrogen
- Density: air 1.204 kg/m³, helium 0.166 kg/m³, hydrogen 0.084 kg/m³.
- Each cubic meter of helium lifts (1.204 − 0.166) × 9.807 = 10.17 N (1 038 g of lift).
- Hydrogen lifts 10.98 N per cubic meter, only 8 percent more than helium, but it burns.
Notes and cautions
- The heat capacity ratio and viscosity are typical values at 20 C. They change a little with temperature.
- Real gases depart from the ideal gas law at high pressure or low temperature; use a compressibility factor Z then.
- Never use these gases without the right safety precautions: hydrogen and methane burn, and nitrogen, argon, helium and CO₂ can displace oxygen in a closed room.
Related tools and guides
- Properties of Air vs Temperature
- Compressed Air Consumption Calculator
- Compressed Air and Gas Flow (guide)
- Ideal Gases and Processes (guide)
- All reference tables
FAQ
What is the density of CO₂?
About 1.83 kg/m³ at 20 C and 1 atm, 1.5 times that of air, so it settles in low places.
Why does helium raise the pitch of the voice?
Sound travels about 3 times faster in helium, which raises the resonant frequencies of the vocal tract.
What is the gas constant for air?
287.05 J/kg·K (the universal gas constant 8 314.46 divided by 28.96).
Sources
- Cengel and Ghajar, Heat and Mass Transfer and Cengel and Boles, Thermodynamics, property appendices; CRC Handbook of Chemistry and Physics (viscosity); molar masses from IUPAC atomic weights.
- Molar masses and typical gas properties at 20 C and 101.325 kPa (standard tables: Cengel and Ghajar, Appendix; CRC Handbook). Calculated: R = 8 314.46 / M, density = P / (R T), kinematic viscosity = dynamic viscosity / density, speed of sound = sqrt(gamma R T). Values for gamma and viscosity are typical and vary a little with temperature.