Question

Speed of sound in helium at 27c temp given molecular weight of helium 4g/mol

Answer 1

You forgot to write " at temperature 27°C "

according to Laplace equation of speed of sound in gas is given by

Now, mixture contains 1 mole of Helium and 2 mole of oxygen,

Molecular mass of mixture :

= (1 × 4 + 2 × 32)/(1 + 2) = 68/3 g/mol = 68/3 × 10⁻³ Kg/mol

For γ of mixture , we should find Cv and Cp

Cv for helium = 3R/2 { because monoatomic }

Cv for oxygen = 5R/2 { because diatomic }

= (1 × 3R/2 + 2 × 5R/2)/(1 + 2) = 13R/6

So, = Cv + R = R + 13R/6 = 19R/6

Now,

Ymix = Cp/Cv = 19/13

Mmix = 0.068/3 kg/mol

Now, speed of sound in mixture =

= 400.9 m/s