[Physics Class Notes] on Properties of Gases Pdf for Exam

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

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 

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. 

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

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.

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.