At high pressures and small volumes, the correction for the volume of the molecules becomes important because the molecules themselves are incompressible and constitute an appreciable fraction of the total volume. The attractive force between molecules initially makes the gas more compressible than an ideal gas, as pressure is raised Z decreases with increasing P. At very high pressures, the gas becomes less compressible Z increases with P , as the gas molecules begin to occupy an increasingly significant fraction of the total gas volume.
Strictly speaking, the ideal gas equation functions well when intermolecular attractions between gas molecules are negligible and the gas molecules themselves do not occupy an appreciable part of the whole volume.
These criteria are satisfied under conditions of low pressure and high temperature. Under such conditions, the gas is said to behave ideally, and deviations from the gas laws are small enough that they may be disregarded—this is, however, very often not the case.
Calculate the pressure of this sample of CO 2 :. The value is somewhat different because CO 2 molecules do have some volume and attractions between molecules, and the ideal gas law assumes they do not have volume or attractions.
Check your Learning A mL flask contains Calculate the pressure of N 2 :. Gas molecules possess a finite volume and experience forces of attraction for one another. Consequently, gas behavior is not necessarily described well by the ideal gas law. Under conditions of low pressure and high temperature, these factors are negligible, the ideal gas equation is an accurate description of gas behavior, and the gas is said to exhibit ideal behavior.
However, at lower temperatures and higher pressures, corrections for molecular volume and molecular attractions are required to account for finite molecular size and attractive forces. The van der Waals equation is a modified version of the ideal gas law that can be used to account for the non-ideal behavior of gases under these conditions. Graphs showing the behavior of several different gases follow. Which of these gases exhibit behavior significantly different from that expected for ideal gases?
Gases C, E, and F. Explain why the plot of PV for CO 2 differs from that of an ideal gas. Under which of the following sets of conditions does a real gas behave most like an ideal gas, and for which conditions is a real gas expected to deviate from ideal behavior? The gas behavior most like an ideal gas will occur under the conditions in b. Molecules have high speeds and move through greater distances between collision; they also have shorter contact times and interactions are less likely.
Deviations occur with the conditions described in a and c. December 01 This Site. Google Scholar. John M. Campbell John M. SPE J. This content is only available via PDF. Copyright has expired. View Metrics. Cited By Web Of Science 8. Email Alerts Article Activity Alert. Latest Issue Alert. Determining Bottomhole Pressures in Pumping Wells.
Print ISSN Resources Terms of Use Privacy Help. Subscribe Subscribe. Calculate the pressure exerted by 0. The non-ideal gas had a greater pressure by 1. An ideal gas is one in which the molecules don't interact with each other and don't take up any space. In an ideal world, collisions between gas molecules are completely elastic. All gases in the real world have molecules with diameters and which interact with each other, so there's always a bit of error involved in using any form of the Ideal Gas Law and van der Waals equation.
However, noble gases act much like ideal gases because they don't participate in chemical reactions with other gases. Helium, in particular, acts like an ideal gas because each atom is so tiny. Other gases behave much like ideal gases when they are at low pressures and temperatures. Low pressure means few interactions between gas molecules occur. Low temperature means the gas molecules have less kinetic energy, so they don't move around as much to interact with each other or their container.
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