9.6 Non-Ideal Gas Behavior

The behavior of a gas is often non-ideal, meaning that the observed relationships between its pressure, volume, and temperature are not accurately described by the gas laws.

The reasons for deviations from ideal gas behavior are considered in this section.

The ideal gas law predicts that gases will exhibit significant deviations from their behavior.

The ideal gas law does not describe gas behavior well at high pressures.

Consider the differences between real gas properties and what a hypothetical ideal gas would look like.

Particles of a hypothetical ideal gas do not attract or repel each other.

Gases gases approximate this behavior at low pressures and high temperatures.

At high pressures, the molecule of a gas are crowded closer together, and the amount of empty space between them is reduced.

Raising the pressure of a gas makes the gas less compressible and increases the fraction of its volume that is occupied by the gas molecule.

Gas molecules are so far apart that they are almost like particles of an ideal gas at low pressures.

The force of attraction is no longer insignificant at higher pressures.
The force pulls the molecule a little closer together, slightly decreasing the pressure if the volume is constant or decreasing the volume at constant pressure because they are less effective in overcoming these attractive forces.

The ideal gas law is better approximated by several different equations.

The first one was developed by the Dutch scientist Johannes van der Waals.

A gas with a relatively low number of molecules occupying a large volume is similar to a gas with a relatively low pressure.

Table 9.3 has experimental values for the van der Waals constants.

The volume of the molecule is important at high pressures and small volumes because they are incompressible and constitute a fraction of the total volume.

The ideal gas equation works well when there are no intermolecular attractions between the gas molecule and the volume.

The gas is said to behave ideally, and deviations from the gas laws are small enough that they may be ignored.

The ideal gas law assumes that CO2 molecules don't have volume or attractions, so the value is somewhat different.

Gases exert force per unit area.

The pressure of a gas can be expressed in the SI unit of pascal or kilopascal, as well as in many other units including torr, atmosphere, and bar.
Other gas pressures can be measured using one of several types of manometers.

The behavior of gases can be described by several laws.

If the volume does not change, the pressure of the gas is proportional to its temperature.
Charles's law states that the volume of a gas sample is proportional to its absolute temperature.
When the temperature is held constant, the volume of gas is proportional to its pressure.
All gases have the same number of molecules under the same conditions.

The ideal gas law can be used to derive a number of equations relating directly measured quantities to properties of interest.

The ideal gas equation may be rearranged to allow the calculation of gas densities.
The law of partial pressures may be used to relate gas pressures to their compositions.
Avogadro's law can be used in computations for chemical reactions.

Gaseous atoms and Molecules move through space.

Transferring gaseous atoms and molecules from high concentration to low concentration is called Diffusion.
gaseous species pass from a container to a vacuum through small orifices.
Graham's law states that the rates of effusion of gases are proportional to the square roots of their atoms.

The ideal gas behavior is explained by a simple but effective model.

The theory assumes that gases consist of widely separated molecules of negligible volume that are in constant motion, colliding elastically with one another and the walls of their container with average velocities determined by their absolute temperatures.
The mass and temperature of the gas affect the distribution of the individual molecule's velocities.

Gas molecule have finite volume and experience forces of attraction.

The ideal gas law does not describe gas behavior well.
The ideal gas equation is an accurate description of gas behavior and the gas is said to exhibit ideal behavior under conditions of low pressure and high temperature.
At lower temperatures and higher pressures, it is necessary to account for the finite size and attractive forces of the molecule.
The van der Waals equation can be used to account for the non-ideal behavior of gases under certain conditions.

The barometric pressure in Denver is 615mm Hg.

The barometric pressure in Kansas City is 740 torr.

The Canadian tire pressure gauge is marked in kilopascals.

The Viking landings on Mars had an average atmospheric pressure of 6.50 bars.

The surface of Venus has an atmospheric pressure of 88.6 atm.

The pressure in a cylinder of gas is described in a medical laboratory catalog.

On a mid-August day in the northeastern United States, the following information appeared in the local newspaper: atmospheric pressure at sea level 29.97 in.

A closed-end manometer is used to measure the pressure of a sample of gas.

Mercury is in the manometer.

The pressure of a sample of gas is measured with a manometer.

Mercury is in the manometer.
The pressure is assumed to be 29.92 in.

A mercury manometer is used to measure the pressure of a sample of gas.

A mercury manometer is used to measure the pressure of a sample of gas.

Open-ended manometers would affect the measurement of a gas using a volatile liquid.

On a hot day, leaving a bicycle in the sun can cause a problem.

Figure 9.12 shows the volume of CH4 gas at 150 K and 1 atm.

A spray can can be used until it is empty except for the propellant gas, which has a pressure of 1344 torr.

A weather balloon has a pressure of 0.992 atm and a temperature of 25 degrees.

The volume of an automobile air bag was inflated at 25 degrees.

Iodine, I2, is a solid at room temperature but becomes a gas when warmed.

A high altitude balloon is filled with 1.41 x 104 L of hydrogen at a temperature of 21 degC and a pressure of 745 torr.

A cylinder of medical oxygen has a volume of 35.4 L and contains O2 at a pressure of 151 atm.

1860 L of air can be supplied to a diver at a pressure of 2.37 atm, which is 45 feet deep.

The average human male consumes 14 L of pure O2 per hour while resting.

A liter of methane gas, CH4, has more hydrogen atoms than a liter of pure hydrogen gas, H2.

Explain why using Avogadro's law as a starting point.

The effect of chlorofluorocarbons on the ozone layer is well known.

1 g of radium decays over a year and produces alpha particles.
The alpha particle becomes an atom.

A balloon that is 100.21 L at 21 degC is released and just barely clears the top of Mount Crumpet in British Columbia.

A 36.0-L cylinder of a gas used for calibration of blood gas analyzers in medical laboratories has 4,880 g N2 and 350 g CO2 in it.

A cylinder of gas mixture used for calibration of blood gas analyzers in medical laboratories contains 5.0% CO2, 12.0% O2, and the remainder N2 at a total pressure of 146 atm.

A sample of gas isolated from unrefined petroleum contains 90.0% CH4, 8.9% C2H6, and 1.1% C3H8 at a total pressure of 307.2 kPa.

A mixture of 0.200 g of H2, 1.00 g of N2, and 0.820 g of Ar is in a closed container.

If the gases exhibit ideal behavior, find the volume of the container.

There are a lot of hydrogen gas and oxygen gas.

A mixture with less than 3.0 % O2 is not.

Concentrations of Hg atoms in the air can be detected by a commercial mercury vapor analyzer.

A sample of carbon monoxide was collected over water at a pressure of 756 torr and a temperature of 18 degrees.

A student collected a sample of gas in an experiment in a chemistry lab.

The pressure of the gas was 753 torr and the temperature was 27 degrees.

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CaCO3 and carbon dioxide are produced by heating calcium carbonate.

Bicycle lights used to be powered by carbide lamps.

Acetylene gas, C2H2, and solid calcium hydroxide were formed by the reaction of CaC2 with water.
The light was provided by the acetylene gas.
The same lamps are used by some cavers, and calcium carbide is used to make acetylene.

A 2.50-L sample of a odorless gas was given at STP.

One molecule of hemoglobin and four molecule of oxygen will work together.

The sample was confined in a bulb with a pressure of 18 torr.

When the pressure was 72 torr, hydrogen was added to the bulb.
There was an electric spark through the mixture.
The final pressure of xenon and unreacted hydrogen in the bulb was 36 torr after the HF was removed.

The van Slyke method is one of the methods used to analyze amino acids.

N2 gas can be formed by reacting with HNO2 and nitrous acid.
The amount of amino acid can be determined from the volume of the gas.
A sample of a biological sample containing CH2(NH2)COOH was analyzed by the van Slyke method and yielded 3.70 mL of N2 collected over water at a pressure of 735 torr.

It takes 6 hours to deflate a balloon filled with helium gas.

Graham's law equation relates the relative rates of effusion for two gases to their molecular mass, and is derived from the definition of rate of effusion and Graham's finding relating rate and molar mass.

When two cotton plugs, one moistened with ammonia and the other with hydrochloric acid, are simultaneously inserted into opposite ends of a glass tube, a white ring of NH4Cl forms.

Explain why a gas uniformly fills a container of any shape using the postulates of the kinetic molecular theory.

Graphs show the behavior of gases.

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