Two ideal gases have the same mass density and the same absolute pressure. One of the gases is helium (He), and its temperature is 298 K. The other gas is neon (Ne). What is the temperature of the neon?

Answer 1

Molar Density = P/RT

At 298 K and 1 atm, both gases would have the same number or molar density. The MASS density of Ne is 20.2/4.0 = 5.05 times that of He, because of its higher atomic weight. To equal the MASS density of He, the Ne would have to have 5.05 times the absolute temperature of the He, or 1505 K.