Hydrogen - Thermophysical Properties

Thermophysical properties of Hydrogen (H2) at 25°C (77°F, 298 K) and atmospheric pressure. Includes molecular weight, density, viscosity, specific heat, thermal conductivity, boiling point, freezing point, critical properties, and heat of combustion.

Property	Value (US Units)	Value (SI Units)
Molecular Weight	—	2.016 g/mol
Specific Gravity (air = 1)	0.070	0.070
Specific Volume	194 ft³/lb	12.1 m³/kg
Density of Liquid at Atmospheric Pressure	4.43 lb/ft³	71.0 kg/m³
Absolute Viscosity	6.05×10⁻⁶ lbm/ft·s	0.009 cP
Sound Velocity in Gas	—	1315 m/s
Specific Heat (cp)	3.42 Btu/lb·°F	14310 J/kg·K
Specific Heat Ratio (cp/cv)	1.405	1.405
Gas Constant (R)	767 ft·lb/lb·°R	4126 J/kg·°C
Thermal Conductivity	0.105 Btu/hr·ft·°F	0.182 W/m·°C
Boiling Point	−423 °F	20.4 K
Latent Heat of Evaporation	192 Btu/lb	447000 J/kg
Freezing/Melting Point	−434.6 °F	−259.1 °C
Latent Heat of Fusion	25.0 Btu/lb	58000 J/kg
Critical Temperature	−399.8 °F	−240.0 °C
Critical Pressure	189 psia	1.30 MN/m²
Critical Volume	0.53 ft³/lb	0.033 m³/kg
Flammable	Yes	Yes
Heat of Combustion	320 Btu/ft³ / 62050 Btu/lb	144000 kJ/kg