Using air as a reference substance, what is the specific gravity of carbon dioxide at 20 degrees Celsius?

Question

Using air as a reference substance, what is the specific gravity of carbon dioxide at 20 degrees Celsius?

Answer 1

Assuming ideal gas, the specific gravity is equal to the ratio of the molar mass of carbon dioxide to air.

All ideal gasses have the same molar density (moles per unit volume). You can easily show this from ideal gas law :

p∙V = n∙R∙T

<=>

n/V = R∙T/p

Multiply by the molar mass and you get the density of the gas

ρ = m/V = M∙n/V = M∙R∙T/p

The specific gravity is equal to ratio of densities:

g_CO2 =  ÃÂ_CO2 / ρ_air

=  (M_CO2∙R∙T/p) / (M_air∙R∙T/p)

= M_C02 / M_air

with

M_CO2 = 44.0099 g/mol

M_air = 28.9644 g/mol (at standard composition)

g_CO2 =  44.0099 / 28.9644 = 1.5194