Core Characteristics of Gases Every Student Should Know
What are Gases?
We say that gas is a state of matter and categorize it into the third category. Gas doesn’t have any shape, size, color, definite volume. So, wherever we place it, it takes the shape of that very container.
The above statement signifies that a gas cannot acquire a definite shape and volume by itself, it always requires a medium to acquire these properties.
There are other properties of gas like temperature, viscosity, volume, weight, entropy, and much more about which we will discuss in this article.
What are the Properties of Gases?
In the above context, we already discussed that gasses do not possess any definite size, shape, and volume; they entirely occupy all the space accessible to them.
The characteristic or properties of gases to fill the available volume within a container is because of the freedom that gas particles bear as they can randomly move in the accessible space.
This determination of movement of gaseous molecules is because of the very weak binding forces among the molecules. In other words, their intermolecular force of attraction is very weak. Because of this, the molecules of a gas are in a continuous motion or we can say a Brownian motion. The below diagram shows the Brownian motion of gas molecules inside the container:
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The motion of gas from one place to another is related to the velocity of gas molecules. So, the higher is the velocity, greater will be the kinetic energy of gas molecules, which in turn, means a quick flow of gas, as we observe in the PNG gas pipeline system in our kitchens. There are many properties of gases; let’s discuss these one-by-one:
Properties of Gases
Compressibility
We say that when gases are compressed, they turn into a liquid state and this fact is true. We can see this in the below figure:
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The compression happens in a way that the molecules set apart in gases come close together and this, in turn, generates a good amount of interatomic force of attraction between these molecules, which is quite similar to the scenario of the molecular spacing and interaction, we observe in liquids.
We often use the term "compressibility" in the field of thermodynamics to describe the deviance in the thermodynamic properties of a real gas from those desired from an ideal gas. We define the compressibility factor with the following equation:
Z = PV/RT
Where,
Z = compressibility
P = Pressure inside the gas molecules
V = Volume of gas
T = Temperature in Kelvin
R = Universal gas constant
Temperature
We hear that the entropy of surroundings keeps on increasing and this fact is very true. If we talk about gases, on rising temperature, the molecules gain super kinetic energy because of which they start colliding with each other and with the walls of the container.
However, on the other hand, if we decrease the temperature, the molecules come closer together and the volume of the gas increases with the decrease in its pressure. It can be explained by Boyle’s law, which is given by:
P α \[\frac{1}{v}\]
Also, temperature is the greatest factor in the kinetic theory of gases.
Expansibility
On rising the pressure, the volume of the gas decreases, as we can see in the pipeline gas system, the gas is passed through the pipe with high pressure. Now, if we increase the temperature, the molecules of this gas gain kinetic energy and because of this, we get a faster supply of gas.
So, pressure and temperature vary inversely with each other and this relationship was explained by Charle’s law, which is as follows:
V α T
Diffusibility
The molecules of the gas remain in perpetual or continual motion which means at a very high velocity.
There is a large amount of intermolecular space amid the gas molecules. When two gases are mixed, particles of one gas can effortlessly pass through the intermolecular space of the other gas, which is known as diffusion, and this property of a gas is called diffusibility. As an outcome both the gases get consistently and entirely mixed. Thus, a mixture of gases at all times remains homogeneous, which is a great feature of diffusibility in gases.
Low Density
As we know that gases have large intermolecular spaces between molecules, they have very large volumes when compared to the mass of the gas. Therefore, gases have fewer densities.
Let’s suppose that 2 ml of water at 78.4 ⁰F is converted into steam at 424 ⁰F and 2-atmosphere pressure or ‘2 atm’, it occupies a volume of 3400 ml.
The Exertion of Pressure on Gas
As solids exert pressure only in the downward direction liquids apply pressure downward as well as to the sides but gases apply pressure in all directions.
A good example is a balloon when we fill the gas inside it, it expands completely. This pressure is because of the breakdown of the particles against the walls of the vessel it is placed in.
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Physical Properties of gas include its color and odor.
FAQs on Properties of Gases: Fundamentals and Applications
1. What are the main physical properties of gases?
Gases exhibit several unique physical properties due to the large distances between their particles. The main properties are:
No Definite Shape or Volume: Gases take the shape and volume of the container they occupy.
High Compressibility: The large intermolecular spaces allow gases to be easily compressed by applying external pressure.
Diffusibility: Gas particles can spread out and mix with each other spontaneously, a property known as diffusion.
Low Density: Gases have much lower densities compared to liquids and solids because their particles are far apart.
Pressure Exertion: Gas particles are in constant, random motion and collide with the walls of their container, exerting pressure.
2. What are the four measurable properties that define the state of a gas?
The state of a gas is defined by four fundamental and measurable properties:
Pressure (P): The force that the gas exerts on the walls of its container. It is commonly measured in atmospheres (atm), pascals (Pa), or millimetres of mercury (mm Hg).
Volume (V): The amount of space that the gas occupies, which is equal to the volume of its container. It is usually measured in litres (L) or millilitres (mL).
Temperature (T): A measure of the average kinetic energy of the gas particles. For gas law calculations, it must be in Kelvin (K).
Amount (n): The quantity of gas present, typically measured in moles (mol).
3. Why are gases highly compressible while solids and liquids are not?
Gases are highly compressible because their constituent particles (atoms or molecules) are very far apart from each other, resulting in large intermolecular spaces. When pressure is applied, these particles can be easily forced closer together, significantly reducing the gas's volume. In contrast, the particles in liquids and solids are already closely packed with very little empty space between them, making them nearly incompressible.
4. What is the difference between an ideal gas and a real gas?
An ideal gas is a theoretical concept used to simplify calculations. It assumes that gas particles have no volume and there are no intermolecular attractive forces between them. It perfectly obeys all gas laws (like Boyle's Law and Charles's Law) under all conditions. A real gas, however, consists of particles that have a finite volume and do experience weak intermolecular forces. Real gases behave most like ideal gases at high temperatures and low pressures, but deviate from ideal behaviour under high pressure and low temperature conditions.
5. How does the property of diffusion in gases apply in everyday life?
Diffusion is the tendency of gas molecules to spread out and mix, moving from an area of higher concentration to lower concentration. A common real-world example is the smell of perfume or air freshener spreading across a room. The fragrant molecules diffuse from the source and mix with the air particles until they are evenly distributed, allowing you to smell them from a distance. Another critical example is the detection of an LPG gas leak, where the added strong-smelling chemical (ethyl mercaptan) diffuses into the surrounding air, alerting us to the danger.
6. How does increasing the temperature affect the pressure of a gas in a fixed container?
Increasing the temperature of a gas inside a container with a fixed volume directly increases its pressure. This happens because temperature is a measure of the average kinetic energy of the gas particles. A higher temperature means the particles move faster and more energetically. As a result, they collide with the walls of the container more frequently and with greater force, which we observe as an increase in pressure.
7. What is meant by the viscosity of a gas?
The viscosity of a gas is its measure of resistance to flow. It arises from the internal friction between layers of the gas moving at different speeds. Unlike liquids, the viscosity of a gas increases as the temperature increases. This is because higher temperatures lead to more frequent collisions between particles, which hinders the overall ordered flow of the gas.
