Gases - Ratios of Specific Heat

A reference tool for the ratios of specific heat (k = cp/cv) for various gases. The ratio of specific heat is a dimensionless property that represents the relationship between specific heat at constant pressure and specific heat at constant volume for ideal gases.

GasRatio of Specific Heat (k)
Acetylene1.3
Air, Standard1.4
Ammonia1.32
Argon1.66
Benzene1.12
N-butane1.18
Iso-butane1.19
Carbon Dioxide1.28
Carbon Disulphide1.21
Carbon Monoxide1.4
Chlorine1.33
Ethane1.18
Ethyl alcohol1.13
Ethyl chloride1.19
Ethylene1.24
Helium1.66
N-heptane1.05
Hexane1.06
Hydrochloric acid1.41
Hydrogen1.41
Hydrogen chloride1.41
Hydrogen sulphide1.32
Methane1.32
Methyl alcohol1.2
Methyl butane1.08
Methyl chloride1.2
Natural Gas (Methane)1.32
Nitric oxide1.4
Nitrogen1.4
Nitrous oxide1.31
N-octane1.05
Oxygen1.4
N-pentane1.08
Iso-pentane1.08
Propane1.13
R-111.14
R-121.14
R-221.18
R-1141.09
R-1231.1
R-134a1.2
Steam (water)1.33
Sulphur dioxide1.26
Toluene1.09

Key Relationships

Internal Energy

For an ideal gas: du = c_v dT

Enthalpy

For an ideal gas: dh = c_p dT

Specific Heat Relationship

For an ideal gas: c_p - c_v = R

where R is the individual gas constant

Ratio of Specific Heat

k = c_p / c_v

where:

  • k = Ratio of Specific Heat (dimensionless)
  • c_p = specific heat at constant pressure (kJ/kgK)
  • c_v = specific heat at constant volume (kJ/kgK)

The ratio is dimensionless and has the same value in both SI and Imperial units.