That is, no pressure applied to a sample of carbon dioxide gas at or above 304K (87.8 degF [31degC]) will induce the gas to liquefy. However, at or below that temperature, the gas can be liquefied if sufficient pressure is applied. For example, a sample of CO2 gas under normal conditions would require a pressure greater than or equal to 738 mmHg (50 psi) to achieve liquid form.
At low pressures, a gas will tend to spread out over a large area rather than remain in a liquid state. So, for a given temperature, less volume means more time for the gas to transition from a gaseous state to a liquid one or vice versa.
Theoretically, any pressure high enough to cause a gas to change phase will also cause it to collapse into a smaller volume, so an ideal pressure could theoretically convert all gases into liquids. In practice, this is not possible because there is a limit on how small you can make a gas before its electrons begin to overlap, forming molecules with stable bonds. But even if it were possible, you would need infinitely high pressures, which no physical system can provide.
In conclusion, only gases that do not interact with each other chemically can be converted into one another by applying pressure. At least two gases must be present for this process to occur.
(xxix) "liquefiable gas" refers to a gas that, while in equilibrium with normal atmospheric pressure, may be liquefied by pressure at -10 oC but will be totally vaporised (760 mm). The gas must be liquid at least at one temperature and normally at any other fixed temperature within the range -80 to 150 oC. It should not be soluble in water at ordinary temperatures.
Liquefiable gases include carbon dioxide, hydrogen sulfide, and various organic compounds. They are usually colourless, odourless, and non-flammable. When mixed together, they produce methane, which is also a liquefiable gas.
Liquefaction of gases is of great importance in many industries including the chemical industry, where gaseous chemicals can be converted into liquids for storage and transportation purposes, and the pharmaceutical industry, where certain medicines cannot be administered orally because they would simply vaporise at body temperature and escape before reaching the stomach or intestines.
The term "liquefiable gas" was first used by Paul Bert in 1872. He described it as a gas that, under pressure, changes state from a gas to a liquid.
Today, most scientists believe that the properties of gases change when they are compressed into liquids.
Water particles in the gas phase move very quickly at 373.99 degrees Celsius. No matter how much pressure is applied to the gas, the gas phase cannot liquefy at any temperature greater than that. Above this temperature, the molecules are too slow to come together before they escape back out into space.
The gas phase of water has a maximum temperature of about 573 degrees Celsius. Even at this high temperature, water remains in its gaseous state.
Any attempt to cool liquid water below its freezing point will cause it to change state from liquid to solid. As soon as the ice crystals form, some small amount of heat must be absorbed by either another object or some internal fluid motions if the sample is not to exceed the melting point and return to a complete state of disorder.
This is why water is said to freeze instantly when exposed to low temperatures. The ice crystals form with no trace of liquid remaining inside their boundary layers. This shows that water becomes a pure crystal at 32 degrees Fahrenheit (0 degrees Celsius).
Above the boiling point, heat must be added to keep water in a liquid state. Vaporized water molecules travel through space rapidly compared to those within a liquid molecule, so any surface immersed in a bath of hot vapor will eventually be heated to the boiling point.
The gases are greatly compressed into a tiny volume when adequate pressure is applied. Gas particles become so close together that they begin to attract one another, forming a liquid. As a result, high pressure and low temperature can be used to liquefy gases. For example, nitrogen at 200 atmospheres (about 30,000 psi) and -258 degrees F becomes a fluid.
Liquefying a gas increases its ability to dissolve other substances, which may be desirable or undesirable depending on the application. For example, fluorine gas is very toxic and will kill most people if it is not handled properly. However, as a liquid it is non-toxic and non-flammable, so it can be safely stored and transported. It also mixes well with other chemicals in a process called "fluorination". The fluoro chemical industry depends on the liquid form of fluorine for efficiency and safety reasons.
There are several methods for liquefying gases. Here we will use cooling to achieve this goal. When a gas enters a cold chamber, it begins to take away energy from its surroundings until it reaches the point where thermal equilibrium is re-established. At this point, all the molecules of the gas have the same speed and direction, and thus no longer contribute to the heat of the system. This is why refrigeration works by removing energy from a system by means of evaporation or condensation.
Natural gas is liquefied by decreasing the hydrocarbon's temperature to around -260 degrees Fahrenheit (-160 degrees Celsius). This temperature reduction liquefies the methane found in natural gas, allowing it to be transported under atmospheric pressure in the form of LNG.
When transported in this form, LNG takes up about one-fifth as much space as gas at normal temperatures and has a much longer transport distance before requiring re-liquefying. The LNG also has a better quality than gas extracted at surface locations because any contaminants (such as water) that might be present in the crude oil used to extract the natural gas will vaporize at the low temperature required for transport.
Liquefaction is only possible with natural gas because it contains mostly methane molecules. Other hydrocarbons such as ethane or propane cannot be transformed into liquid form at standard temperatures. However, these gases can be converted into substances called "mono-methyl-hydrazine" and "di-methyl-hydrazine", which are then further processed into nitrogen and carbon dioxide, respectively. These chemicals can then be recycled and reused.
The main advantage of LNG over other forms of transportation is its capacity to provide heat when it is warmed back up to room temperature. This makes LNG useful for areas where it gets cold at night, such as northern Canada and the United States.