Specific Heat Capacity Gases

Reference data and engineering information about specific heat capacity gases for thermodynamics applications.

specificheatcapacitygasesCalculatorData Table

Overview

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The specific heat capacity of a gas describes how much energy is required to change its temperature. Gases have two distinct values: c_p (constant pressure) and c_v (constant volume). Their ratio, κ = c_p/c_v, governs isentropic processes such as compression and expansion in turbines, compressors, and nozzles.

For an ideal gas the individual gas constant satisfies:

R = c_p − c_v

All values below are approximate at 20 °C (68 °F) and 1 atm (14.7 psia).

Key Formulas

Relationship	Equation	Description
Specific heat ratio	κ = c_p / c_v	Also called the isentropic exponent
Individual gas constant	R = c_p − c_v	Derived from Mayer's relation
Universal gas constant	R̄ = M · R	R̄ ≈ 8.314 kJ/(kmol·K)
Specific heat at constant volume	c_v = R / (κ − 1)	From combining the two relations above
Specific heat at constant pressure	c_p = κ · R / (κ − 1)	Equivalently c_p = κ · c_v

Variables

Symbol	Meaning	Typical SI Unit
c_p	Specific heat at constant pressure	kJ/(kg·K)
c_v	Specific heat at constant volume	kJ/(kg·K)
κ	Specific heat ratio (isentropic exponent)	dimensionless
R	Individual gas constant	kJ/(kg·K)
R̄	Universal gas constant (≈ 8.314)	kJ/(kmol·K)
M	Molar mass	kg/kmol

Specific Heat Capacity Data

15 rows

Specific heat capacity of common gases at 20 °C, 1 atm (approximate)
Gas or Vapor	Formula	c_p(kJ/(kg·K))	c_v(kJ/(kg·K))	c_p(Btu/(lbm degF))	c_v(Btu/(lbm degF))	κ	R(kJ/(kg·K))	R(ft lbf/(lbm degR))
Acetone	(CH₃)₂CO	1.47	1.32	0.35	0.32	1.11	0.15
Acetylene	C₂H₂	1.69	1.37	0.35	0.27	1.232	0.319	59.34
Air	—	1.007	0.718	0.24	0.17	1.4	0.287	53.34
Ammonia	NH₃	2.16	1.66	0.52	0.4	1.31	0.53	96.5
Argon	Ar	0.52	0.312	0.12	0.07	1.667	0.208
Benzene	C₆H₆	1.09	0.99	0.26	0.24	1.12	0.1
Bromine	Br₂	0.25	0.2	0.06	0.05	1.28	0.05
Butane	C₄H₁₀	1.67	1.53	0.395	0.356	1.094	0.143	26.5
Carbon dioxide	CO₂	0.846	0.655	0.21	0.16	1.289	0.189	38.86
Carbon monoxide	CO	1.02	0.72	0.24	0.17	1.4	0.297	55.14
Carbon disulphide	CS₂	0.67	0.55	0.16	0.13	1.21	0.12
Chlorine	Cl₂	0.48	0.36	0.12	0.09	1.34	0.12
Chloroform	CHCl₃	0.63	0.55	0.15	0.13	1.15	0.08
Ethanol	C₂H₅OH	1.88	1.67	0.45	0.4	1.13	0.22
Methanol	CH₃OH	1.93	1.53	0.46	0.37	1.26	0.39

Source: engineeringtoolbox.com

Monoatomic vs Diatomic Gas Comparison

Specific Heat Ratio κ by Gas

Calculator: Derive c_p from R and κ

For an ideal gas with known individual gas constant R and specific heat ratio κ, you can compute both specific heats.

Ideal Gas Specific Heats from R and κ

Individual gas constant R(kJ/(kg·K))

Specific heat ratio κ

Unit Converter

The source page included a specific heat Unit Converter. This migrated converter preserves the common engineering units for gas specific heat and gas constants.

Gas Specific Heat Unit Converter

Specific heat(kJ/(kg K))

Individual gas constant(kJ/(kg K))

Temperature(K)

Restored Original Source Tables

The following tables are restored from the original source page to preserve the complete reference data.

Gases - Specific Heats and Individual Gas Constants

The source table includes SI columns for cp and cv, Imperial columns for cp and cv in Btu/(lbm °F), the ratio cp/cv, and the individual gas constant R = cp - cv in both kJ/(kg K) and ft lbf/(lbm °R). All of those original data columns are retained below; the final two columns represent the source's cp-cv / individual gas constant values.

47 rows

Gases - Specific Heats and Individual Gas Constants
Gas or Vapor	Formula	cp (kJ/kgK)	cv (kJ/kgK)	cp (Btu/(lbmoF))	cv (Btu/(lbmoF))	κ = cp/cv	cp-cv (kJ/kgK)	cp-cv (ft lbf/(lbmoR))
Acetone	(CH3)2CO	1.47	1.32	0.35	0.32	1.11	0.15
Acetylene	C2H2	1.69	1.37	0.35	0.27	1.232	0.319	59.34
Air		1.007	0.718	0.24	0.17	1.4	0.287	53.34
Alcohol (ethanol)	C2H5OH	1.88	1.67	0.45	0.4	1.13	0.22
Alcohol (methanol)	CH3OH	1.93	1.53	0.46	0.37	1.26	0.39
Ammonia	NH3	2.16	1.66	0.52	0.4	1.31	0.53	96.5
Argon	Ar	0.52	0.312	0.12	0.07	1.667	0.208
Benzene	C6H6	1.09	0.99	0.26	0.24	1.12	0.1
Blast furnace gas		1.03	0.73	0.25	0.17	1.41	0.3	55.05
Bromine	Br2	0.25	0.2	0.06	0.05	1.28	0.05
Butane	C4H10	1.67	1.53	0.395	0.356	1.094	0.143	26.5
Carbon dioxide	CO2	0.8459	0.655	0.21	0.16	1.289	0.189	38.86
Carbon monoxide	CO	1.02	0.72	0.24	0.17	1.4	0.297	55.14
Carbon disulphide	CS2	0.67	0.55	0.16	0.13	1.21	0.12
Chlorine	Cl2	0.48	0.36	0.12	0.09	1.34	0.12
Chloroform	CHCl3	0.63	0.55	0.15	0.13	1.15	0.08
Coal gas		2.14	1.59
Combustion products		1		0.24
Ethane	C2H6	1.75	1.48	0.39	0.32	1.187	0.276	51.5
Ether (diethyl ether)	(C2H5)2O	2.01	1.95	0.48	0.47	1.03	0.06
Ethylene	C2H4	1.53	1.23	0.4	0.33	1.24	0.296	55.08
Chlorodifluoromethane, R-22	CHClF2					1.18
Helium	He	5.251	3.12	1.25	0.75	1.667	2.08	386.3
Hexane	C6H14					1.06
Hydrochloric acid		0.795	0.567
Hydrogen	H2	14.32	10.16	3.42	2.43	1.405	4.12	765.9
Hydrogen Chloride	HCl	0.8	0.57	0.191	0.135	1.41	0.23	42.4
Hydrogen Sulfide	H2S			0.243	0.187	1.32		45.2
Hydroxyl	OH	1.76	1.27			1.384	0.489
Krypton	Kr	0.25	0.151
Methane	CH4	2.22	1.7	0.59	0.45	1.304	0.518	96.4
Methyl Chloride	CH3Cl			0.24	0.2	1.2		30.6
Natural Gas		2.34	1.85	0.56	0.44	1.27	0.5	79.1
Neon	Ne	1.03	0.618			1.667	0.412
Nitric Oxide	NO	0.995	0.718	0.23	0.17	1.386	0.277
Nitrogen	N2	1.041	0.743	0.25	0.18	1.4	0.297	54.99
Nitrogen tetroxide	N2O4	4.69	4.6	1.12	1.1	1.02	0.09
Nitrous oxide	N2O	0.88	0.69	0.21	0.17	1.27	0.18	35.1
Oxygen	O2	0.9189	0.659	0.22	0.16	1.395	0.26	48.24
Pentane	C5H12					1.07
Propane	C3H8	1.67	1.48	0.39	0.34	1.13	0.189	35
Propene (propylene)	C3H6	1.5	1.31	0.36	0.31	1.15	0.18	36.8
Water Vapor Steam 1 psia. 120 – 600 oF	H2O	1.93	1.46	0.46	0.35	1.32	0.462
Steam 14.7 psia. 220 – 600 oF	H2O	1.97	1.5	0.47	0.36	1.31	0.46
Steam 150 psia. 360 – 600 oF	H2O	2.26	1.76	0.54	0.42	1.28	0.5
Sulfur dioxide (Sulphur dioxide)	SO2	0.64	0.51	0.15	0.12	1.29	0.13	24.1
Xenon	Xe	0.16	0.097

Source: engineeringtoolbox.com

For conversion of units, use the Specific heat online unit converter.

See also tabulated values of specific heat capacity of food and foodstuff, metals and semimetals, common liquids and fluids, common solids and other common substances as well as values of molar heat capacity of common organic substances and inorganic substances.

Engineering Notes

See also specific heat for common solids, food and foodstuff, metals and semimetals, liquids and fluids, and other related heat-capacity tables.
Ideal-gas assumption: The listed values assume ideal-gas behaviour. At high pressures or near the saturation line, real-gas corrections (departure functions) become significant.
Temperature dependence: Specific heats increase with temperature, especially for polyatomic gases. The values here apply near 20 °C; for combustion or cryogenic work, use temperature-dependent correlations (e.g., polynomial fits from NIST-JANAF tables).
Monatomic gases (He, Ar, Ne) have κ ≈ 5/3 = 1.667, a theoretical result from kinetic theory. Diatomic gases near room temperature have κ ≈ 1.4.
Specific heat ratio κ directly sets isentropic relations: T₂/T₁ = (p₂/p₁)^((κ−1)/κ). A small error in κ can propagate into large errors in compressor or turbine outlet temperatures.
Blast furnace gas and other fuel-gas mixtures should be treated with caution—composition varies with process conditions.
R = c_p − c_v holds exactly only for ideal gases. For real gases, Mayer's relation includes a correction term involving the equation of state.
The individual gas constant R is related to the universal gas constant R̄ by R = R̄ / M, where M is the molar mass in kg/kmol.

References

Engineering ToolBox – Specific Heat of Gases

Source: engineeringtoolbox.com