Rank the following atoms and molecules based on which would effuse the fastest. i) H2  ii) He iii) N2 iv) CO2 v) H2S

Question – Rank the following atoms and molecules based on which would effuse the fastest.

i) H₂ 

ii) He

iii) N₂

iv) CO₂

v) H₂S

Solution –

Molecular mass of H₂ = 1 x 2 = 2

Molecular mass of He = 4

Molecular mass of N₂ = 2 x 14 = 28

Molecular mass of CO₂ = 12+ 16 = 44

Molecular mass of H₂S = 2 x 1 + 32 = 34

Effusion of gases also depends upon their molecular mass at constant temperature and pressure. According to Graham’s law ,

r_{1 /} r₂ = √ M₂/M₁

r ∝ 1 / √ M

Hence gas with lowest molecular mass will effuse faster.

Decreasing order of molecular mass of gases is,

CO₂ , H₂S, N₂ , He , H₂

Decreasing order of rate of effusion ,

H₂ , He , N­₂ , H₂S , CO₂

H₂ will effuse fastest and Co₂ will effuse slowest.