Compute the root-mean-square speed of Ar molecules in a sample of argon gas at a temperature of 79°C.

Question

__m s^-1

Answer 1

v_rms = √3RT/MW

v_rms = root mean square velocity

R = gas constant = 8.3145 kg·m²/s²/K·mol (note the units used for R in this case,& see below)**

T = temp in K = 79C + 273 = 352K

MW = molar mass = 39.9 g/mol = 0.0399 kg/mol (note units used here to match those used for R)

v_rms = √(3)(8.3145 kg-m²/s²/Kmol)(352K) / 0.0399 kg

v_rms = 469.1 m/s

** You may be used to seeing R as 8.3145 J/K-mol but since 1 J = 1 kg-m²/s², we substitute these units