Gases are all around us. Many of them are vital to our life. The oxygen we breathe reacts with certain nutrients such as carbohydrates or lipids to give us energy. We exhale carbon dioxide and water. Plants take up carbon dioxide and water vapor to convert back in to oxygen and nutrients in the presence of sun light.
Other gases in the atmosphere have different roles. For an example, plants cannot use atmospheric nitrogen directly. Certain micro organisms called nitrogen fixing bacteria take up nitrogen and convert it to nitrates.
Some of the gases are responsible for the green house effect. These gases include; water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorocarbons (CFxClx) and tropospheric ozone (O3).
Characteristic properties of gases
There are some general Characteristic of gases which distinguish them from solids and gases. These are called Characteristic properties of gases. Some of them are listed as follows.
1. They are easy to compress - compressibility.
In General, compressibility is the ability of something to be "squashed" into a smaller space. Gases are easy to compress even with relatively little pressure. An internal combustion engine is a good example. Compared to gases, liquids are very less compressible. How about solids ? You can understand the compressibility of solids, if you try to squeeze a big table in to very small room. It is really hard!
2. They expand to fill their containers- expandability.
We know that gases tend expand until they fill whatever contains them. Therefore, it is safe to assume that the volume of gas is equal to the volume of its container.
3. They occupy far more space than the liquids or solids at the same pressure from which they form.
Generally, the volume of a liquid or solid increases approximately 800 times when it forms a gas. This large change in volume can be utilized to do work such as steam engine. Here, the escaping steam can be made to do work. Same phenomenon occurs on a much smaller scale when we "POP" popcorn. When the kernel of popcorn is heated in oil, the liquid inside the kernel turns in to gases. The pressure build up inside the kernel is enormous and the kernel eventually explodes.
Common gases at room temperature
It might be useful to understand which elements or compounds are gases at room temperature.
According to this table, we can observe several patterns.
1. Both elements (eg: He) and compounds (eg: CO2) may be gases room temperature.
2. Elements that are gases at room temperature are all non metals (eg: He, O2).
3. Compounds that are gases at room temperature are all covalent compounds (eg: CO2,NH3)
4. All these gases have relatively small molecular weights but there may be rare exceptions.
Some of the common gases at room temperature.
Element or compound
|
Molecular Weight
|
H2 (hydrogen)
|
2.02
|
He (helium)
|
4.00
|
CH4 (methane)
|
16.02
|
NH2 (ammonia)
|
17.03
|
Ne (neon)
|
20.18
|
HCN (hydrogen cyanide)
|
27.03
|
CO (carbon monoxide)
|
28.01
|
N2 (nitrogen)
|
28.01
|
NO (nitrogen oxide)
|
30.01
|
C2H6 (ethane)
|
30.07
|
O2 (oxygen)
|
32.00
|
PH3 (phosphine)
|
34.00
|
H2S (hydrogen sulfide)
|
34.08
|
HCl (hydrogen chloride)
|
36.46
|
F2 (fluorine )
|
38.00
|
Ar (argon)
|
39.95
|
CO2 (carbon dioxide)
|
44.01
|
N2O ( dinitrogen oxide)
|
44.01
|
C3H8 (
propane)
|
44.10
|
NO2 (nitrogen dioxide)
|
46.01
|
O3 (ozone)
|
48.00
|
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