• 1.) Gases are all around us, but although many, such as perfume, can be smelt, most gases are invisible. Like liquids, gases can flow but, unlike solids or liquids, gases will not stay where they are put. They have no set shape or volume, and they expand in every direction to fill completely whatever container they are put into. If the container has no lid, the gas escapes.
  • 2.) In 1811, Avogadro suggested the principle that equal volumes of gases contain equal number of molecules or atoms under identical conditions of temprature and pressure. This direct relationship between the number of moles and volume is written in equation form and shown graphically.
  • 3.) Vapour is a gas that has evaporated from a liquid before the liquid has reached its boiling point. Water, for example, boils to form a gas at 100°C (212°F). But, even at much lower temperatures, some water particles escape from the liquid to form a gas, called vapour, that mixes with the air. When vapour cools slightly, the gas forms droplets seen as mist.
  • 5.) In hot air balloons, a burner heats the air inside. This causes the particles of air to gain more energy and so they move faster and farther apart from one another, pushing at the sides of the balloon. Heat always causes gases to expand. If you left a balloon near a fire, the air inside could expand so much that the balloon would burst.
  • 6.) Why does a champagne cork explode out of a shaken bottle? The champagne inside the bottle contains lots of tiny bubbles of gas. Shaking the bottle releases the gas, and the high-speed gas particles bang against the cork. This creates an enormous pressure on the cork, and eventually forces the cork out of the bottle.
  • 7.) You might hear the term vapor. Vapor and gas mean the same thing. The word vapor is used to describe gases that are usually liquids at room temperature. Good examples of these types of liquids include water (H2O) and mercury (Hg). They get the vapor title when they are in a gaseous phase. You will probably hear the term “water vapor” which means water in a gas state. Compounds such as carbon dioxide (CO2) are usually gases at room temperature. Scientists will rarely talk about carbon dioxide vapor.
  • 8.) Gases hold huge amounts of energy and their molecules are spread out as much as possible. When compared to solids or liquids, those spread out gaseous systems can be compressed with very little effort. Scientists and engineers use that physical trait all of the time. Combinations of increased pressure and decreased temperature force gases into containers that we use every day.
  • 9.) You might have compressed air in a spray bottle or feel the carbon dioxide rush out of a can of soda. Those are both examples of gas forced into a smaller space at greater pressure. As soon as the gas is introduced to an environment with a lower pressure, it rushes out of the container. The gas molecules move from an area of high pressure to one of low pressure. 

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