Identification of Properties of Gases

Through the study of gases, we can gain a better understanding of the behaviour of matter at its most fundamental level, that of individual particles acting independently and nearly totally free of interactions and interferences with one another. It is through this knowledge of gases that we will be able to gain a better understanding of the far more complicated condensed phases (liquids and solids), in which the theory of gases will no longer provide us with correct answers, but it will still serve as a useful model that will at the very least assist us in rationalising the behaviour of these more complicated states of matter.

Gas have no definite Volume or Shape

We know that a gas has no definite volume or shape; a gas will fill whatever space is made available to it by the surrounding environment. This is in stark contrast to the behaviour of a liquid, which always exhibits a distinct upper surface when its volume is less than the volume of the space it occupies. Gases have a number of distinct distinguishing characteristics as compared to liquids and solids, one of which is their low density. In comparison, one mole of liquid water at 298 K and one atmosphere of pressure occupies a volume of 18.8 cm3, whereas the same quantity of water vapour at the same temperature and pressure occupies a volume of 30200 cm3, which is more than 1000 times larger.

The most amazing property of gases, on the other hand, is that they all respond in the same way to changes in temperature and pressure, expanding or contracting by predictable amounts in reaction to these changes. A significant difference exists between this and the behaviour of liquids or solids, in which case the qualities of each specific substance must be defined individually.

The Pressure of a Gas

Gaseous molecules are always in motion and as a result, they regularly collide with the inner walls of their container. The objects quickly bounce off the container walls with no loss of kinetic energy, but the reversal of direction (acceleration) causes a force to be applied to the container walls. The pressure of the gas is equal to the product of this force divided by the whole surface area on which it operates.

In order to determine the pressure of a gas, it is necessary to measure the pressure that must be applied externally in order to prevent the gas from expanding or contracting. Consider the following illustration: a gas is trapped in a cylinder with one end enclosed by a freely moving piston; the other end is open. The piston must have a particular amount of weight (more precisely, a force, f) applied to it in order to perfectly balance the force exerted by the gas on the piston’s bottom and the force that tends to push it up in order to keep the gas contained in the container. For a given cross-sectional area of the piston, the pressure of the gas can be calculated as follows: f/A = pressure of the gas

What are the Properties of Gases?

1. Compressibility

Particles of gas have large intermolecular gaps in the middle of them, which allows them to move freely. By applying pressure to the particles, a significant amount of space can be reduced and the particles are brought closer together. As a result, the volume of gas produced can be significantly reduced. Compressing the gas is what this is referred to as.

When we increase the pressure from one atmosphere to two atmospheres, the volume of gas is compressed to half its original size, however if the volume of water were reduced in the same way, the volume would be reduced by only 0.00001 parts per million.

In addition to decreasing the temperature, decreasing the volume of a gas is possible. When the temperature is lowered, the quantity of energy in the particles decreases, and their mobility decreases, causing them to move less away from one another and closer together. As a result, the intermolecular pull becomes more prominent, and the particles become closer together in the process. The volume of the gas is reduced as a result of this.

2. Expansibility

When pressure is applied to a gas, it contracts as a result. When pressure is released, the gas expands, and this is known as the expansion effect.

Increasing the temperature causes the particles to gain more energy, travel quicker, and disperse further away from one another. Because of this, the intermolecular attraction becomes less noticeable. The volume of the gas grows.

3. Diffusibility

A very high velocity is maintained by the molecules of the gas, which are always in motion. In between the molecules, there is a significant quantity of intermolecular space. When two gases are mixed, particles of one gas can easily move through the intermolecular gap of the other gas, whereas particles of the other gas cannot. Both gases are totally and reliably combined as a result of this procedure. As a result, a mixture of gases maintains its homogeneity at all times.

4. Low Density

Because gases have extensive intermolecular gaps, their volumes are disproportionately enormous when compared to their mass. As a result, they have lower population densities. If one millilitre of water at 39.2 degrees Fahrenheit is turned into one millilitre of steam at 212 degrees Fahrenheit( and one atmospheric pressure), it will fill a volume of 1700 millilitres.

5. Exertion of Pressure

Solids only exert downward pressure; liquids do not exert downward pressure. Liquids exert downward and sideways pressure on the surface of the liquid. However, gases exert pressure in every direction (a good sample is a balloon). Pressure is created by the bombardment of particles against the vessel’s walls, which causes the vessel to expand.

Conclusion

Gases are characterised by the lack of a definite volume or shape. They completely occupy all of the available surface area. The characteristic or properties of gases to fill the available volume within a container are the outcome of the freedom that gas particles have to move anywhere in the available space when they are released from a container. The fact that gaseous molecules can move independently of one another is due to the extremely weak binding forces that exist between them. In other words, the intermolecular interactions between the molecules are quite weak. As a result, the molecules of a gas are in constant motion and are associated with high velocities and, consequently, large kinetic energies.