Basic Hydrogen Properties

Data including density, flammability range, and autoignition energy for hydrogen.

Hydrogen Properties
Properties Value Units
Auto ignition temperature [3,a] 500-585 °C
  1085 °F
Boiling point (1 atm) [b] -252.9 °C
  -423.2 °F
Density NTP [1,b] 0.08375 kg/m³
  0.005229 lb/ft³
Diffusion coefficient in air NTP [1, a] 0.610 cm²/s
  6.57 E-4 ft²/s
Enthalpy NTP [1, b] 3858.1 kJ/kg
  1659.8 Btu/lb
Entropy NTP [1, b] 53.14 J/g-K
  12.70 Btu/lb-°R
Flame temperature in air [a] 2045 °C
  3713 °F
Flammable range in air [1,a] 4.0 - 75.0 vol%
Ignition energy in air [c] 2.0 E-5 J
  1.9 E-8 Btu
Internal Energy NTP [1, 2, b] 2648.3 kJ/kg
  1139.3 Btu/lb
Molecular weight [b] 2.02  
Specific gravity (air = 1) NTP [1, c] 0.0696  
Specific volume NTP [1,b] 11.94 m³/kg
  191.26 ft³/lb
Specific heat at constant pressure , Cp NTP [1, b] 14.29 J/g-K
  3.415 Btu/lb-°R
Specific heat at constant volume, Cv NTP [1, b] 10.16 J/g-K
  2.428 Btu/lb-°R
Thermal conductivity NTP [1, b] 0.1825 W/m-K
  0.1054 Btu/ft-h-°R
Viscosity NTP [1,b] 8.813 E-5 g/cm-sec
  5.922 E-6 lb/ft-sec
Attachment: 
Notes: 
  • NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm
  • Reference state: Internal Energy U=0 at 273.16 K for saturated liquid; Entropy S=0 at 273.16 K for saturated liquid.
  • The autoignition temperature depends on hydrogen concentration (minimum at stoichiometric combustion conditions), pressure, and even the surface characteristics of the vessel.  Reported figures range from 932-1085 oF according to source [a].
Source