Heat capacity ratio

Heat capacity ratio for various gases[1][2]
Gas Temp. [°C] γ
H2 −181 1.597
−76 1.453
20 1.410
100 1.404
400 1.387
1000 1.358
2000 1.318
He 20 1.66
Ar −180 1.760
20 1.670
O2 −181 1.450
−76 1.415
20 1.400
100 1.399
200 1.397
400 1.394
N2 −181 1.470
Cl2 20 1.340
Ne 19 1.640
Xe 19 1.660
Kr 19 1.680
Hg 360 1.670
H2O 20 1.330
100 1.324
200 1.310
CO2 0 1.310
20 1.300
100 1.281
400 1.235
1000 1.195
CO 20 1.400
NO 20 1.400
N2O 20 1.310
CH4 −115 1.410
−74 1.350
20 1.320
NH3 15 1.310
SO2 15 1.290
C2H6 15 1.220
C3H8 16 1.130
Dry air -15 1.404
0 1.403
20 1.400
200 1.398
400 1.393
1000 1.365

In thermal physics and thermodynamics, the heat capacity ratio, also known as the adiabatic index, the ratio of specific heats, or Laplace's coefficient, is the ratio of the heat capacity at constant pressure (CP) to heat capacity at constant volume (CV). It is sometimes also known as the isentropic expansion factor and is denoted by γ (gamma) for an ideal gas[note 1] or κ (kappa), the isentropic exponent for a real gas. The symbol γ is used by aerospace and chemical engineers. where C is the heat capacity, the molar heat capacity (heat capacity per mole), and c the specific heat capacity (heat capacity per unit mass) of a gas. The suffixes P and V refer to constant-pressure and constant-volume conditions respectively.

The heat capacity ratio is important for its applications in thermodynamical reversible processes, especially involving ideal gases; the speed of sound depends on this factor.

  1. ^ White, Frank M. (October 1998). Fluid Mechanics (4th ed.). New York: McGraw Hill. ISBN 978-0-07-228192-7.
  2. ^ Lange, Norbert A. (1967). Lange's Handbook of Chemistry (10th ed.). New York: McGraw Hill. p. 1524. ISBN 978-0-07-036261-1.


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