Topic 8:  Gases and Condensation

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a) What are the characteristics of gases? (Properties, uses)

Gases are the least complex state of matter.  Gases have very low density compare to liquids and solids.  For example 1 mol of oxygen gas (32.0g) has a volume of roughly 22 400mL compared with 1 mol of water (18.0g) with a volume of 18.0 mL or 1 mol of aluminum metal (27.0g) with a volume of 10.0 mL.  Gases are easily compressed because there is so much space between particles compared to a solid or liquid.

The atmosphere is a sea of gases.

The molecular composition of the atmosphere provides the perfect conditions for life to exist on Earth.  For example, the oxygen we breathe is generally abundant in supply.  The atmosphere provides protection from the sun, and it helps keep Earth at a comfortable temperature.

Gases found in the atmosphere.

How does this layer of gases keep the Earth warm?  More than half of the sun’s radiant energy that is directed toward Earth is absorbed by the surface.

b) What behaviors are described by the gas laws? (Gas laws)

You will now study a series of mathematical relationships that relate the four variables described in the last section to kinetic molecular theory.  Each of the four variables is represented by a symbol.

P = pressure exerted by the particles

V = volume occupied by the particles

T = temperature in Kelvin’s of the particles

n = number of moles of the particles

These symbols define the mathematical expressions known as the gas laws.  Using the gas laws, you can make predictions about how the volume of a fixed amount of gas will respond to changes in pressure and temperature.

Charles's law provides a basic for absolute temperature.

Absolute temperature scale--a temperature measurement made relative to absolute zero--the lowest possible temperature.

Charles's law states the volume of a gas at constant pressure is directly proportional to the absolute temperature.

For example if a balloon is in a eighty to ninety degree room then it will be bigger than if it was in thirty degree room.  Why?  When it is warmer the molecules are moving faster and they don’t want to be next to each other so they expand.  When it is cold and the molecules want to come together because it is cold so the balloon will be smaller.

  This is around 80°F HOT.

This is around 30°F COLD.

Boyle's law describes a pressure-volume relationship.

Boyle's Law states the volume of a gas at constant temperature is inversely proportional to the pressure.

For example if you puss on the plunger, you are compressing the trapped gas particles into a smaller space.  In the smaller space, the particles collide with the walls more often, and more collisions result in a higher pressure.

c) What conditions will cause a gas to condense? (Forces of attraction, temperature)

Forces of attraction.  At low temperature, gas particles slow down.  At high pressures, gas volumes are reduced, the gases still differ from the ideal because of particle size.  Conditions are such that particle size and the attractive forces between particles significantly affect particle volume.  If temperature is low enough and the pressure is high enough, the attractive forces between particles will be so strong that the gas will condense to form a liquid or solid.