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KE per molecule = 3/2 kT = 3/2 * 1.38e-23 * 300 = 6.21e-21 (J) KE per mole: 3/2 RT = 3.74 kJ In the next calculations, it is suggested that the pressure is equal to the standard pressure. Let's suggest that the volume of the gas at 298.2 K is 1 m3. At 273.2 K the gas would have a volume of 1*273.2/298.2 = 0.916 m3 which is 40.9 moles = 2.46e25 molecules. So, The ND is 2.46e25 molecules / m3 at 298.2K The concentration is 40.9 moles / m3