Passage IV

An ideal gas is a hypothetical gas that behaves exactly as predicted by the ideal gas law. Depending on the conditions, an ideal gas may or may not be a good model for a real gas. The compressibility factor (z) is a value that quantifies the deviation of a gas from ideal behavior. Figure 1 shows, for an ideal gas and for 5 real gases, how z varies with pressure (in atmospheres, atm) at 0 ℃. Table 1 shows how the volume of 1 mole (6 × 10²³ atoms or molecules) of gas varies with pressure for an ideal gas, for 3 of those 5 real gases, and for air.

Figure and table adapted from E. D. Eastman and G. R. Rollefson, Physical Chemistry, 1st ed. ©1947 by McGraw-Hill Book Co.