why can helium be compressed?
Yes. All gases can be compressed.
which is a greenhouse gas.
First, Jaqcueline, if you have a question, it is much better to put it in as a separate post in <Post a New Question> rather than attaching it to a previous question, where it is more likely to be overlooked.
Since this is not my area of expertise, I searched Google under the key words "greenhouse gas" to get these possible sources:
http://en.wikipedia.org/wiki/Greenhouse_gas
http://www.eia.doe.gov/bookshelf/brochures/greenhouse/Chapter1.htm
http://www.epa.gov/climatechange/emissions/index.html
(Broken Link Removed)
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
I hope this helps. Thanks for asking.
A greenhouse gas is a gas which, when added to the atmosphere, prevents the Earth's infrared radiation from being reradiated back to space, and therefore acts as an insulating "blanket" to make the Earth warmer. Water vapor is not considered a greenhouse gase because there is so much of it, that radiation cannot escape at its broad range of absorbing wavelengths anyway. The most important greenhouse gases causing global warming are CO2 and CH4.
Helium can be compressed because it is a gas at room temperature and low pressure, but it can transform into a liquid or even a solid when it is subjected to very high pressure and low temperature. This is a general property of gases - they have high compressibility.
To understand why helium can be compressed, we need to look at the behavior of its molecules. Helium is composed of very small, light atoms, which means that the intermolecular forces between helium atoms are relatively weak compared to other gases. These forces are called Van der Waals forces or London dispersion forces. Since the intermolecular forces are weak, helium atoms are not tightly packed together like in a solid or a liquid. Instead, they are free to move around and have a lot of empty space between them.
When we compress a gas like helium, we apply external pressure, which reduces the volume of the gas. As the gas is compressed, the molecules get closer to each other, decreasing the amount of empty space between them. This increases the density of the gas and makes it more compact.
However, there are limits to how much helium can be compressed. As the pressure increases, the intermolecular forces start coming into play. At extremely high pressures, the weak intermolecular forces between the helium atoms become significant and cause the gas to condense into a liquid or solid phase. The transition to a liquid or solid state occurs at very low temperatures as well, making it difficult to achieve for everyday applications.
In conclusion, helium can be compressed due to the weak intermolecular forces between its atoms. However, there are limits to compressibility, and at very high pressures and low temperatures, it will transition into a liquid or solid state.