# Why is helium gas more viscous than nitrogen gas?

The Chapman-Enskog equationmay be used to estimate viscosity for a dilute gas. This equation is based on semi-theorethical assumption by Chapman and Enskoq. The equation requires three empirically determined parameters: the collision diameter (σ), the maximum energy of attraction divided by the Boltzman constant (є/к) and the collision integral (ω(T*)). η0*10^7=266.93*[(M*T)^(1/2)]/ [σ^2*ω(T*)] ·T*=κT/ε Reduced temperature (dimensionless) ·η0 = viscosity for dilute gas (uP) ·M = molecular mass (g/mol) ·T = temperature (K) ·σ = the collision diameter (Å) ·ε / κ = the maximum energy of attraction divided by the Boltzman constant (K) ·ωη = the collision integral So you can see that since nitrogen has a higher moecular mass M, then it will have a higher ratio in the 2nd term of this equation, therefore it will have a higher viscosity than helium. This is your answer.

Errenhius’ Equation. Patricles with smaller mass move faster. A nitrogen molecule is much larger than a helium atom.