CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
An unknown monatomic gas is studied at 350 K. The measured compressibility factors up to 70 atm are listed below.
Pressure (atm) → 1 30 70
Z → 0.97 0.85 0.95
Beyond 70 atm no measurements were taken.
(a) Sketch a qualitative Z versus P curve for this gas from 1 atm up to 200 atm. Your sketch should pass smoothly through the three measured points and extend to 200 atm. Clearly label the approximate pressure at which Z is expected to equal 1 again.
(b) Using molecular-level reasoning, justify the shape of the curve you drew, including why Z must eventually rise above 1 at sufficiently high pressure.
(c) Compare the likely magnitudes of the van der Waals constants a and b for the unknown gas to those of helium. State whether each constant is expected to be larger, smaller, or about the same, and justify your answer by referring to features of the Z versus P behavior you described.