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Methane (CH₄): Thermophysical Properties and Phase Diagram

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Methane, CH4 , is a colorless odorless gas. It is also known as marsh gas or methyl hydride. The vapors are lighter than air.
Methane is easily ignited. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket.

Methane is used as feed stock to chemical industry and is the main constituent of the fuel natural gas .

Methane phase diagram

Chemical, physical and thermal properties of methane:
Values are given for gas phase at 25 °C (77 °F, 298 K) and 1 atm., if not other phase, temperature or pressure given.

For full table with Imperial Units - rotate the screen!

Methane - Thermophysical Properties
Property Value Unit Value Unit Value Unit Value Unit
Autoignition temperature 810 K 537 °C 999 °F
Boiling Point 111.51 K -161.6 °C -259.0 °F
Critical density 10.139 mol/dm3 162.7 kg/m3 0.3156 slug/ft3 10.15 lb/ft3
Critical Pressure 4.5992 MPa=MN/m2 45.99 bar 45.39 atm 667.1 psi=lbf/in2
Critical Temperature 190.56 K -82.59 °C -116.66 °F
Critical Volume 98.63 cm3/mol 0.00615 m3/kg 3.169 ft3/slug 0.0985 ft3/lb
Density, gas 41.0 mol/m3 0.657 kg/m3 0.00127 slug/ft3 0.0410 lb/ft3
Density, gas at STP; 32°F/0°C 1 atm 44.7 mol/m3 0.7168 kg/m3 0.00139 slug/ft3 0.0447 lb/ft3
Density, liquid at -260 °F/-162°C 26429 mol/m3 422.6 kg/m3 0.820 slug/ft3 26.38 lb/ft3
Flammable, gas and liquid yes
Flash point 85 K -188 °C -306 °F
Gas constant - R 518.28 J/kg K 0.1440 Wh/(kg K) 3099 (ft lbf/slug °R) 96.329 (ft lbf/lb °R)
Gibbs free energy of formation -51 kJ/mol -3179 kJ/kg -1367 Btu/lb
Heat (latent) of vaporation 8.19 kJ/mol 511 kJ/kg 219.48 Btu/lb
Specific heat, Cp 35.8 J/mol K 2.232 kJ/kg K 0.533 Btu/lb°F or cal/g K
Specific Heat, Cv 27.4 J/mol K 1.709 kJ/kg K 0.408 Btu/lb°F or cal/g K
Heat of combustion -890.8 kJ/mol -55528 kJ/kg -23.9 Btu/lb
Heat(enthalpy) of formation -75.00 kJ/mol -4675 kJ/kg -2010 Btu/lb
log KOW (Octanol/Water Partition Coefficient) 1.09
Melting point 90.55 K -182.6 °C -296.7 °F
Molecular Weight 16.042 g/mol 0.03537 lb/mol
Solubility in water 0.022 mg/ml
Sound velocity 446 m/s
Specific Gravity (density relativ to air), 0°C/32°F 0.554
Specific Heat Ratio - Cp/Cv 1.31
Specific Volume 0.0244 m3/mol 1.52 m3/kg 784.44 ft3/slug 24.38 ft3/lb
Standard molar entropy, S° 186 J/mol K 11.59 kJ/kg K 2.77 Btu/lb °F
Surface tension at -161 °C / -258 °F 14 dynes/cm 0.014 N/m
Thermal Conductivity 0.0339 W/m°C 0.019587 Btu/hr ft °F
Triple point pressure 0.011696 MPa=MN/m2 0.117 bar 0.115 atm 1.70 psi=lbf/in2
Triple point temperature 90.69 K -182.456 °C -296.42 °F
Vapor (saturation) pressure 62.12 MPa=MN/m2 466000 mm Hg 613.07 atm 9010 psi=lbf/in2
Vapor (saturation) pressure at 38 °C /100 °F 34.47 MPa=MN/m2 258574 mm Hg 340.18 atm 4999 psi=lbf/in2
Viscosity, dynamic (absolute) 0.01107 cP 7.44 (lbm/ft s ×10-6) 0.23 (lbf s/ft2 ×10-6)
Viscosity, kinematic 17.08 cSt 183.8 (ft2/s ×10-6)

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Follow the links below to get values for the listed properties of methane at varying pressure and temperature :

See also more about atmospheric pressure, and STP - Standard Temperature and Pressure & NTP - Normal Temperature and Pressure,
as well as Thermophysical properties of: Acetone, Acetylene, Air, Ammonia, Argon, Benzene, Butane, Carbon dioxide, Carbon monoxide, Ethane, Ethanol, Ethylene, Helium, Hydrogen, Hydrogen sulfide, Methanol, Nitrogen, Oxygen, Pentane, Propane, Toluene, Water and Heavy water, D2O.

Methane is a gas at standard conditions. However, at low temperature and/or high pressures the gas becomes a liquid or a solid.

The methane phase diagram shows the phase behavior with changes in temperature and pressure. The curve between the critical point and the triple point shows the methane boiling point with changes in pressure.

At the critical point there is no change of state when pressure is increased or if heat is added.

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

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