Maxwell-Boltzmann distribution gives the average (equilibrium) molecular speed as v ¯ ¯ = 2 π π v p = 2 2 π π ⋅ ⋅ k B T m where v p is the most probable speed. We note that k B ⋅ ⋅ N A = R and M = m ⋅ ⋅ N A