Gases, Properties of (Encyclopedia of Science)
Gases are a state of matter characterized by two properties: their lack of definite volume and their lack of definite shape. This definition suggests, in the first place, that a given mass of gas can occupy any volume whatsoever. Imagine a cylindrical tank filled with a small amount of hydrogen gas placed in a chemistry laboratory. If the top is removed from that tank in a room, the gas escapes from the tank to fill the room. If the door to the room is opened, the gas then escapes to fill the building. If the building door also is opened, the gas escapes into the outside environment and, at least in theory, then expands throughout the universe. Neither solids nor liquids, the other two common forms of matter, display this property.
Gases also take the shape of the container in which they are placed. Suppose the valve of the tank of hydrogen gas is fitted with a rubber hose that leads to a cubic box. When the valve is opened, the hydrogen gas fills the cubic box. Its shape changes from cylindrical to cubic. Liquids also take the shape of their container, although solids do not.
Kinetic theory of matter
Our understanding of the properties of gases arises from the kinetic theory of matter. The kinetic theory of matter says that all matter is made
(The entire section is 1200 words.)
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Gases, Properties of (Encyclopedia of Nursing & Allied Health)
The fundamental physical properties of a gas are related to its temperature, pressure, and volume. These properties can be described and predicted by a set of equations known as the gas laws. While these laws were originally based on mathematical interpretations for an ideal or perfect gas, modern atomic and kinetic theory of gases has led to a modified expression that more accurately reflects the properties of real gases.
Current understanding of gas properties came as a result of study of the interaction between volume, pressure, and temperature. Robert Boyle was the first to describe the relationship between the volume and pressure of a gas. In 1660 he learned that if an enclosed amount of a gas is compressed to half its original volume while the temperature is kept constant, the pressure will double. He expressed this mathematically as PV = constant, where P stands for pressure, V stands for volume, and the value of the constant depends on the temperature and the amount of gas present. This expression is known as Boyle's law.
The second fundamental property of gases was defined by Jacques Charles in 1787. He found that the temperature and volume of a gas are directly related. Charles observed that a number of gases expanded equally as heat was applied and the pressure was kept constant.
Charles's ideas were expanded upon in research by others in the field, most notably Joseph Gay-Lussac, who also studied the thermal expansion of gases. The volume/temperature relationship is known as Charles's law.
The third property of gases was described by Gay-Lussac who, in addition to his work with volume and temperature, researched the connection between pressure and temperature. In 1802, he formulated an additional law. These three laws can be combined into one generalized equation that expresses the interrelation between pressure, temperature and volume. This equation, called the ideal gas law, is written as PV = nRT.
While the ideal gas law works very well in predicting gas properties at normal conditions, it does not accurately represent what happens under extreme conditions. Neither does it account for the fact that real gases can undergo phase change to a liquid form. Modern atomic theory helps explain these discrepancies. It describes molecules as having a certain freedom of motion in space. Molecules in a solid material are arranged in a regular lattice such that their freedom is restricted to small vibrations about lattice sites. Gas molecules, on the other hand, have no macroscopic spatial order, and they can move about their containers at random. The motion of these particles can be described by the branch of physics known as classical mechanics. The study of this particulate motion is known as the kinetic theory of gases. It states that the volume of a gas is defined by the position distribution of its molecules. In other words, the volume represents the available amount of space in which a molecule can move. The temperature of the gas is proportional to the average kinetic energy of the molecules, or to the square of the average velocity of the molecules. The pressure of a gas, which can be measured with gauges placed on the container walls, is a function of the particle momentum, which is the product of the mass of the particles and their speed.
The human body requires certain gases to function. Oxygen and carbon dioxide are respiratory gases that move between the blood and air through the lungs. Respiratory gases are exchanged between the body and the environment through the mechanisms of convection and diffusion.
Convection is also called mass flow. Convection moves the air from the air in the environment into the lungs. Convection also moves the blood between the body tissues and the lungs. Diffusion moves the oxygen and carbon dioxide across membranes and transports gases between air and blood in the lungs and between blood and respiratory tissues in the body.
Role in human health
The gases in the human body that are most significant are oxygen and carbon dioxide. If the gases are not exchanged in the proper quantities and adequately transported through the body, then both minor and major health problems can result.
Common diseases and disorders
Many common diseases or disorders can affect the adequate exchange of gases throughout the human body. These diseases or ailments can range from severe respiratory diseases, such as emphysema, to the common cold. Both lung disease and heart disease can lead to abnormalities in the composition of blood gases. Following is a list of just a few of the diseases or disorders that can cause abnormalities in the exchange of gases in the human body.
- chronic obstructive pulmonary disease
- congestive heart failure
Ideal gas lawhe mathematical expression that predicts the behavior of a "perfect" gas.
Kinetic theory of gaseshe physical principles that describe how gas molecules interact.
Holum, John R. Fundamentals of General, Organic and Biological Chemistry. Wiley and Sons, 1994.
Tortora, Gerard, and Sandra Grabowski, eds. Principles of Anatomy and Physiology, 8th edition. New York: Harper Collins, 1996.
Adcock, Louis H. "The Egg in the Bottle Revisited: Gas pressure and Amonton's Law (Charles's Law)." Journal of Chemical Education 75, no. 12 (Dec. 1998):1567.
"Physical Properties of Gases." Pump.Net <<a href="http://pump.net/thebasics/physpropgases.htm">http://pump.net/thebasics/physpropgases.htm>.
Peggy Elaine Browning