Determine the density of NH3 gas at 435 K and 1.00 atm?

Question

Haven't learned this yet. Need help understanding...

Answer 1

Density is mass per unit volume. If the number of moles of anything is known, then we know the mass via the molecular weight. So, in the case of the ideal gas, PV = nRT, we can replace the number of moles (n) with mass (m) divided by molecular weight (M): PV=(m/M)RT. Now all we have to do is rearrange the equation to: m/V = PM/RT, which equals density. Substituting (molecular weight of ammonia is 17 g/mole):

d = (1 atm) (17 g/mole) / (0.0821 L*atm/K*mole) (435 K)

d = 0.0047 g/L, or 4.7 mg/L.