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Unformatted text preview: Gases Gases have very low densities, and may be compressed or expanded easily: in other words, gases expand or compress to completely f ll whatever container they are in. Gases also tend to Form homogeneous mixtures, that is they tend to mix completely to Form uniForm mixtures. Solids and liquids oFten Form heterogeneous mixtures. Gases exert a pressure or a Force where the gas particles collide with a surFace. Remember, gas particles are moving randomly with high kinetic energy. Everywhere they collide, the Force oF the collision is the pressure that the gas exerts. Pressure units are many and varied: torr, mm Hg, bar, psi, atm, and Pa or kPa. Scientists typically use atmospheres, atm, where sea level atmospheric pressure (called standard atmospheric pressure) is exactly 1 atm. Although atm is quite commonly used, the SI unit oF pressure is actually Pascals, Pa, where 1 atm = 1.01325kPa. In the US, our barometers (what we use to measure atmospheric pressure), usually read in mm Hg or in torr, where 1 atm = 760 mm Hg = 760 torr. Kinetic-Molecular Theory of Gases The special properties of gases have been explained by a series of assumptions, called the Kinetic-Molecular Theory: 1) Gases consist of large numbers of particles that are in continuous, random motion. This is why gases mix relatively quickly and form uniform mixtures. 2) The volume of the particles of gases is negligible compared to the volume of empty space between the particles. In fact, gas particles typically take up only about 0.1% of the total volume of their containers, the rest being empty space. In contrast, liquids occupy about 70% of their total volume. 3) Attractive and repulsive forces between gas particles is negligible. Therefore, there are no appreciable intermolecular forces and all of the gas particles act essentially independently of one another....
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This note was uploaded on 06/25/2008 for the course CHEM 400-401 taught by Professor Dr.samples during the Fall '06 term at American River.
- Fall '06