GAS PROPELLANTS

High speed of sound is a desirable feature of gun and rocket propellants. The following formula denotes that low molecular mass and high temperature increase the speed of sound. Hydrogen and helium are called light gases because they have low molecular mass.

speed of sound = A0 = (GRT/M)0.5

where:
G is the ratio of specific heat at constant pressure to specific heat at constant volume
R is the gas constant (8.314 J mol -1 K -1)
T is the absolute temperature
M is the molecular mass
substance G
(ratio of
specific
heats)		 M
(molecular
mass)
[kg/mol]		 speed of
sound at
300 K
temperature
[m/s]		 speed of
sound at
1200 K
temperature
[m/s]
dry air 1.39 0.0288 347 694
ammonia (NH3) 1.29 0.017 435 870
helium (He) 1.64 0.004 1011 2023
hydrogen (H2) 1.45 0.002 1346 2691
methane (CH4) 1.30 0.016 451 901
nitrogen (N2) 1.38 0.028 350 700
oxygen (O2) 1.41 0.032 331 662

substance G
(ratio of
specific
heats)		 M
(molecular
mass)
[kg/mol]		 speed of
sound at
407 K
temperature
[m/s]
steam (H2O) 1.30 0.034 494
Curator: Al Globus
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