Question

Calculate the de Broglie wavelength of a Helium atom moving at a speed of 50 m/s.

Answer 1

molar mass of He = 4.003 g/mol

This is mass of 6.022*10^23 atoms

we have below equation to be used:

mass of 1 atom = molar mass /(6.022*10^23)

mass of 1 atom = 4.003/(6.022*10^23)

mass of 1 atom = 6.635*10^-24 g

so, we have:

v = 50 m/s

mass, m = 6.635*10^-24 g

= 6.635*10^-27 kg [using conversion 1 Kg = 1000 g]

we have below equation to be used:

wavelength = Planck constant / (mass*velocity)

wavelength = (6.626*10^-34) / (6.635*10^-27*50)

wavelength = 2.0*10^-9 m

Answer: 2.0*10^-9 m