CHEMISTRY · Single correct · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Three separate 1.00 mol samples of He, Ar, and NH3 are each placed in identical rigid 5.00 L containers at 250 K. The measured pressures are as follows:
He: 4.1 atm
Ar: 3.8 atm
NH3: 2.9 atm
Which statement is most consistent with these observations?
(a) Finite molecular volume reduces the free space inside the container; because NH3 has the largest molecular size, its pressure shows the greatest negative deviation from the ideal value.
(b) The strength of attractive intermolecular forces increases from He to Ar to NH3, producing progressively larger negative deviations from ideal behavior.
(c) Because NH3 has the greatest molar mass, it exerts the lowest pressure according to the ideal gas law, whereas He, the lightest gas, shows the highest pressure.
(d) Attractive intermolecular forces decrease from He to Ar to NH3, so the deviation from ideality becomes increasingly positive across the series.