Chem 112 Exam AID Course Pack

# 325 kpa is 224 l if you forget you can calculate

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Unformatted text preview: which are in the wrong orientation to have overlap of any kind (neither positive or negative addition 4.0 Gas Laws Major Properties of Gases - little interaction between molecules - individual molecules are far apart - individual molecules have relatively high kinetic energy - compressible (and exert pressure) to a significant degree Molecules which are gases at room temperature tend to have weak intermolecular forces. For example, small non- branched alkanes (methane, ethane, etc) are gases at room temperature, but increasing size (and increasing London dispersion forces) raises the boiling point each time. Molecules that hydrogen bond will have higher boiling points than similar molecules that will not. Gas Pressure à༎ the amount of force a gas exerts on its surroundings/container. Force (N) Pressure (Pa) = Area (m2 ) Taking this further: • From physics we know that Force=mass x gravity • The volume of a fluid in a cylinder is: Volume= cross sectional area x height € o V= A x h à༎ rearrange for A à༎ A=V/h • Substituting these into our original pressure equation we get: mgh P= V • We also know that density is mass divided by volume. Therefore we can substitute further ending with: P = density × gravity × height € Properties of Ideal Gases € Ethan Newton & Barry Zhang for SOS Winter 2012 15 - molecules are point particles (no volume) molecules travel in straight lines only – intermolecular forces (and gravity) have negligible effect on motion collisions are perfectly elastic (no loss of kinetic energy all ideal gases act the same way all ideal gases at the same average kinetic energy have the same temperature, and vice versa (called the Principle of Equipartition of Energy) all ideal gases obey the Ideal Gas Law We can also simply say that ideal gases follow the postulates of the Kinetic Molecular Theory. (All of the above are postulates or consequences of the KMT). Most gases are approximately ideal under normal conditions, and the KMT helps explain why they sometimes deviate from this: − They become less ideal as temperature drops (slower- moving molecules à༎ intermolecular forces act over longer periods of time as molecules pass each other and thus are more significant) or as pressure increases (less space to move in à༎ more collisions, plus molecules are closer to each other, making intermolecular forces stronger). − A real gas approaches the behaviour of ideal gases at the extremes of...
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