Ideal gas behavior, deviations from

Ideal gases obey the ideal gas law at all temperatures and pressures. However, there are no ideal gases, only real gases. Real gases deviate from ideal behavior most strongly at high pressures and/or low temperatures. So, where do the basic tenets of Kinetic Molecular Theory fail ... 

Answer This is a very long problem—and you won t be asked to solve a problem this complex on the AP test. It can also show you the degree to which different gases deviate from ideal behavior. 

An equation of state relates the molar quantity and volume of a gas to temperature and pressure. The simplest and most widely used of these relationships is the ideal gas equation of state (the familiar PV = nRT), which, while approximate, is adequate for many engineering calculations involving gases at low pressures. However, some gases deviate from ideal behavior at nearly all conditions and all gases deviate substantially at certain conditions (notably at high pressures and/or low temperatures). In such cases it is necessary to use more complex equations of state for PVT calculations. 

You should be aware of how real gases deviate from ideal behavior. Van der Waals equation ... 

Real Gases Deviations from Ideal Behavior... 

REAL GASES DEVIATIONS FROM IDEAL BEHAVIOR... 

REAL GASES DEVIATIONS FROM IDEAL BEHAVIOR We learn that real gases deviate from ideal behavior because the gas molecules have finite volume and because attractive forces exist between molecules. The van der Waab equation gves an accurate account of real gas behavior at high pressures arxJ low temperances. 

List two reasons why gases deviate from ideal behavior. 

The basic assumptions of the kinetic-molecular theory of gases give us insight into why real gases deviate from ideal behavior. The molecules of an ideal gas are assumed to occupy no space and have no attraction for one another. Real molecules, however, do have finite volumes and do attract one another. As Figure 10.21 shows, the unoccupied space in which real molecules can move is less than the container volume. At low pressures, the combined volume of the gas molecules is negligible relative to the container volume. Thus, the unoccupied volume available to the molecules is essentially the container volume. 

REAL GASES DEVIATIONS FROM IDEAL BEHAVIOR (SECTION 10.9) Departures from ideal behavior increase in magnitude as pressure increases and as temperature decreases. Real gases depart from ideal behavior because (1) the molecules possess finite volume and (2) the molecules experience attractive forces for one another. These two effects make the volumes of real gases larger and their pressures smaller than those of an ideal gas. The van der Waals equation is an equation of state for gases, which modifies the ideal-gas equation to account for intrinsic molecular volume and intermolecular forces. 

Gases deviate from ideal behavior at very high pressures and very low temperatures. Under these conditions, the gas laws would not necessarily hold. 

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