SpecificGasConstant
Calculate the specific gas constant Rs = R / M for any gas using molar mass. Free online thermodynamics calculator with gas presets (air, CO2, He, H2) and comparison charts.
About This Calculator
The specific gas constant (Rs) is a gas-specific constant derived from the universal gas constant R divided by the gas molar mass M. It appears in the specific form of the ideal gas law P = ρ·Rs·T, where ρ is density. Engineers and scientists use Rs in compressible fluid dynamics, pipeline flow calculations, compressor design, aerodynamics, and meteorology.
The formula is Rs = R / M, where R = 8.314462618 J/(mol·K) and M must be in kg/mol. For example, dry air has a molar mass of 28.9647 g/mol (0.0289647 kg/mol), giving Rs = 287.058 J/(kg·K). Lighter gases like helium have a much higher Rs (2077 J/(kg·K)), while heavy gases like chlorine have a lower value (117 J/(kg·K)).
This calculator supports selecting from 12 common gases with preset molar masses or entering a custom molar mass. The results include a step-by-step breakdown and a comparison bar chart showing Rs values across all preset gases.
Frequently Asked Questions
What is the specific gas constant?
The specific gas constant Rs is the universal gas constant R divided by the molar mass M of the gas. It has units of J/kg·K and is used in the specific form of the ideal gas law: P = ρ·Rs·T where ρ is density.
How do you calculate specific gas constant?
Rs = R / M where R = 8.314462618 J/(mol·K) is the universal gas constant and M is the molar mass in kg/mol. Alternatively, Rs = Cp − Cv where Cp and Cv are the specific heat capacities at constant pressure and volume.
What is the specific gas constant of air?
The specific gas constant of dry air is approximately 287.058 J/kg·K, calculated using a molar mass of 28.9647 g/mol.
What are the units of specific gas constant?
The specific gas constant is measured in joules per kilogram-kelvin (J/kg·K). In SI base units this is m²/(s²·K).
How is specific gas constant used in engineering?
The specific gas constant is essential in thermodynamics for compressible fluid flow calculations, pipeline design, compressor sizing, aerodynamics, and meteorology. It directly relates pressure, density, and temperature in the ideal gas law.
Does specific gas constant vary between gases?
Yes, each gas has a unique specific gas constant because it depends on molar mass. Light gases like hydrogen have a high Rs (4124 J/kg·K), while heavy gases like chlorine have a low Rs (117 J/kg·K).
Whats the specific gas constant of hydrogen?
The specific gas constant of hydrogen H2 is 4124.2 J/kg·K calculated from its molar mass of 2.016 g/mol.
What is the difference between universal and specific gas constant?
The universal gas constant R (8.314 J/mol·K) applies to one mole of any ideal gas. The specific gas constant Rs = R/M applies to one kilogram of a specific gas, making it unique to each gas.