Here are the most important things about gases to remember:
- Gases assume the shape and volume of their container.
- Gases have lower densities than their solid or liquid phases.
- Gases are more easily compressed than their solid or liquid phases.
- Gases will mix completely and evenly when confined to the same volume.
- All elements in Group VIII are gases. These gases are known as the noble gases.
- Elements that are gases at room temperature and normal pressure are all nonmetals.
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How do they make liquid helium, liquid oxygen, liquid nitrogen… atoms that are normally in the gases state?
The basic idea is that they compress the gas (remember the room full of ping pong balls? Now squish the room so it’s only half the size. Do the balls bounce faster or slower? Faster! So the temp increases.) When they compress the gas, it heats it up, so they cool it, then squish it even more to higher pressure and cool to near room temperature. They keep repeating this until it becomes a very high pressure, then finally they release the pressure (which is like suddenly expanding the squished room to the size of a football field), which makes the temperature drop way fast and the gas becomes extremely cold, condensing into a liquid.
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