6: Properties of Gases
The gaseous state of matter is the only one that is based on a simple model that can be developed from first principles. As such, it serves as the starting point for the study of the other states of matter.
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- 6.1: Observable Properties of Gas
- The invention of the sensitive balance in the early seventeenth century showed once and for all that gases have weight and are therefore matter. Guericke's invention of air pump (which led directly to his discovery of the vacuum) launched the “pneumatic era" of chemistry long before the existence of atoms and molecules had been accepted. Indeed, the behavior of gases was soon to prove an invaluable tool in the development of the atomic theory of matter.
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- 6.3: Dalton's Law
- Although all gases closely follow the ideal gas law PV = nRT under appropriate conditions, each gas is also a unique chemical substance consisting of molecular units that have definite masses. In this lesson we will see how these molecular masses affect the properties of gases that conform to the ideal gas law. Following this, we will look at gases that contain more than one kind of molecule— in other words, mixtures of gases. We begin with a review of molar volume and the E.V.E.N. principle.
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- 6.4: Kinetic Molecular Theory (Overview)
- The kinetic molecular theory of gases relates macroscopic properties to the behavior of the individual molecules, which are described by the microscopic properties of matter. This theory applies strictly only to a hypothetical substance known as an ideal gas; we will see, however, that under many conditions it describes the behavior of real gases at ordinary temperatures and pressures quite accurately, and serves as the starting point for dealing with more complicated states of matter.
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- 6.5: More on Kinetic Molecular Theory
- In this section, we look in more detail at some aspects of the kinetic-molecular model and how it relates to our empirical knowledge of gases. For most students, this will be the first application of algebra to the development of a chemical model; this should be educational in itself, and may help bring that subject back to life for you! As before, your emphasis should on understanding these models and the ideas behind them, there is no need to memorize any of the formulas.
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- 6.6: Real Gases and Critical Phenomena
- When the temperature is reduced, or the pressure is raised in a gas, the ideal gas begins to break down, and its properties become unpredictable; eventually the gas condenses into a liquid. It is vital for appreciating the limitations of the scientific model that constitutes the "ideal gas".