Methane (CH₄): Thermophysical Properties and Phase Diagram

Chemical, Physical and Thermal Properties of Methane - CH₄. Phase diagram included.

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=lb_f/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	(lb_m/ft s ×10^-6)	0.23	(lb_f s/ft² ×10^-6)
Viscosity, kinematic	17.08	cSt	183.8	(ft2/s ×10-6)

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

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.

Methane phase diagram C

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.