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Name: Max
Status: student
Grade: 9-12
Location: NY
Country: USA
Date: Winter 2011-2012


Question:
Why is it that a gas like butane can be compressed into a liquid and stored at room temperature (for example in simple plastic containers of disposable lighters), while compressed liquid hydrogen must be stored at very low temperatures in reinforced containers? What is the physical mechanism, which makes butane easier to compress and store at room temperature than hydrogen?



Replies:
Max, it is the attraction between the molecules that makes this possible. Butane molecules are chemically more attracted to each other (they would rather be near each other than far apart in a gas) than hydrogen molecules. The biggest factor is molecular weight - it takes more energy for a butane molecule to break away from its 'friends' (evaporate). The higher the temperature, the easier it is for a molecule to break away because higher temperature means more (vibrational) energy. But at the same temperature, hydrogen molecules evaporate much more readily than butane. They have much lower attraction to each other. At room temperature, to get hydrogen molecules to be very close together (because their molecular attraction is low), it requires a lot more pressure than butane does.

Hope this helps, Burr Zimmerman



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