Question

What is the de Broglie wavelength of a nitrogen molecule in air at 300 K? Assume that the molecule is moving with the root-mean square speed of molecules at this temperature. (Atomic mass of nitrogen = 14.0076 u)

Answer 1

Temperature of the nitrogen molecule, T = 300 K
Atomic mass of nitrogen = 14.0076 u
Hence, mass of the nitrogen molecule, m = 2 × 14.0076 = 28.0152 u
But 1 u = 1.66 × 10⁻²⁷ kg
m = 28.0152 ×1.66 × 10⁻²⁷ kg
Planck’s constant, h = 6.63 × 10⁻³⁴ Js
Boltzmann constant, k = 1.38 × 10⁻²³ J K⁻¹

Therefore, the de Broglie wavelength of the  nitrogen molecule is 0.028 nm.