Question

the H2 : He molecular ratio for Neptune is approximately 4.0 : 1.0, and other gases are so rare that they can be ignored. Assuming that the relative molecular mass of H2 is 2.0 and He is 4.0, calculate the following.

i.The average relative molecular mass .

ii.Average mass in kg of a molecule in Neptune’s atmosphere. Show your working in each case.

iii. The density of Neptune’s atmosphere at 1.0 bar is 0.45 kg m−3. Assuming that Neptune’s atmosphere behaves as an ideal gas, calculate the temperature at the 1 bar level using the equation T = (Pm) / (1.38*10^-23)p. Show your working, including the derivation of units for your final answer. T = (Pm) / (1.38*10^-23)p

Answer 1

i)

The molecule of hydrogen is H₂ and for helium it is He

On the surface of Neptune H₂:He molecular ratio is 4:1

i.e.  H₂:He = 4:1 (molecular ratio)

molecular mass of hydrogen molecule = 2 u

molecular mass of Helium molecule is = 4 u

average relative molecular mass can be calculated as,

(4*2)+(1*4) = 8 + 4 = 12 g/mol

ii)

average mass in kilogram (kg) in Neptune's atmosphere is,

iii)

to calculate the temperature

given

density (p_m) = 0.45 kg/m³

pressure (p) = 1 bar

Substituting the values T = 73.15 K