Specific gas constant

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The specific gas constant of a gas is given by the universal gas constant, divided by the molar mass of the gas.

Contents

[edit] Definition

Let:

R \be the universal gas constant, or about 8.314472 \mathrm{\frac{J}{mol \ K}} \
r \be the specific gas constant for the gas you are working with
M \be the molar mass of the gas

So then:

r = {\frac{R}{M}} \ -or rewritten as- R = rM \

[edit] Examples

[edit] Helium

The molar mass of helium is:

0.004003 \mathrm{\frac{kg}{mol}}

Therefore, the specific gas constant of helium is:

\mathrm{{\frac {8.314472 {\frac{J}{mol \ K}}}{ 0.004003{\frac{kg}{mol}} }} \approx 2077 {\frac{J}{kg \ K}}}\

[edit] Air

The generally accepted molar mass of air is:

0.02897 \mathrm{\frac{kg}{mol}}

Therefore, the specific gas constant of air is:

\mathrm{{\frac {8.314472 {\frac{J}{mol \ K}}}{0.02897{\frac{kg}{mol}} }} \approx 287 {{\frac{J}{kg\ K}}}}
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