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CHAPTER 6 : GASES
As studied in Chapter 5 (States of Matter) a gas has
no bounding surface and thus has no definite volume or shape.
In this chapter, we examine and learn to use the laws
governing the behavior of gases. These laws, combined with the other properties
of gases, form the basis for the Kinetic molecular theory of gases.
6.1 Properties of Gaseous State
Following are the five properties of gases which
can be measured experimentally.
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1.
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Gases are easily compressible.
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The molecules in a gas are very far apart due to
very low intermolecular forces. By external pressure they can be
brought closer, thereby compressing the gas.
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2.
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Gases do not have definite volume.
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Molecules move easily and occupy the entire volume
of the container and take the shape of the container.
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3.
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Gases exert pressure in all directions.
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Molecules are always in a state of rapid zig zag
motion, colliding with each other and with the walls of the container.
Collisions account for pressure. As the same number of molecules
strike a given surface in unit time, gases exert pressure uniformly
in all directions.
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4.
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Gases diffuse easily.
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Molecules of other substances can fill a large
space between gaseous molecules. This is nothing but diffusion.
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5.
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Gases have low
density.
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Due to large space, the number of units of molecules
per unit volume of gas is very low compared to solids or liquids.
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Gas Laws :
The quantitative relationship between volume, pressure,
temperature and the rate of diffusion for a given quantity of gas are
termed as ’Gas Laws’.
These Laws are
* Boyle’s law
* Charles’ law
* Pressure-temperature
law
* Avogadro’s law
* Graham’s law of diffusion
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