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Gas Laws
Gas Laws: Some Basic Principles
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Let's begin our exploration of the gas laws by observing a demonstration. The video will begin with a can of soda being heated on a hot plate (see photo above). All the soda has been removed from the can and replaced with a small amount of water. The water inside the can is now boiling and the inside of the can is filled with water vapor. Observe what happens when the can is taken from the hot plate and then immediately inverted into an ice water bath. Click here to watch.
Why did the can collapse?
When the soda can was placed in the ice water bath, most of the water vapor inside the can condensed, greatly reducing the number of gas molecules exerting a force on the inside walls of the can. There was then not enough force on the inside of the can to counteract the atmospheric gas molecules which were bombarding the container on the outside. Thus, the can was crushed.
Air is a mixture of roughly 80% nitrogen and 20% oxygen by volume. But what if it were, let's say, pure nitrogen? Would the can have been crushed just as easily under similar conditions? Or what if air were 100% oxygen, or another mixture ratio for that matter?
The answer lies in the fact that gases, unlike liquids and solids, have almost no intermolecular attractions under ordinary conditions of temperature and pressure. Every gas molecule acts as an independent particle. Furthermore, every gas molecule in a sample of nitrogen gas will behave in very much the same way as every gas molecule in a sample of oxygen gas. Had air been 100% nitrogen, or 100% oxygen, or any other ratio of the two, the can would have been crushed just as a dramatically, whatever the case.
Since dissimilar gases exhibit remarkably similar characteristics, gas laws exist which apply to virtually every gas under ordinary conditions. This activity will give you a chance to discover these laws and how molecular behavior influences them.
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