Behaviour of Gas Molecules

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What is Gas?

The properties and laws obeyed by the molecules of the gas dictate the behavior of gas molecules. Physicists have encountered many differences among the molecular distribution of a gas and a liquid or a solid substance. To explain the tendency and the distribution of molecules in a gas, gas laws, and gas properties have been developed.

The kinetic theory of gas molecules explains the behavior of gas molecules. We can study the gas molecules at a microscopic level.

Here are some points which state about the kinetic theory of gases:

  • A gas is composed of the collaboration of a large number of molecules.

  • The larger number of distances among the gas molecules make the volume of the gas almost negligible.

  • There is a minor amount of intermolecular interactions found in gas.

  • The collision of the gas molecules is elastic. It doesn’t matter if it is between themselves or with the wall of the container.

What is Gas in Science?

Scientists have discovered that gas is a homogeneous fluid. A gas possesses low viscosity and density. It is found that the volume of the container is identical to the volume of the gas.

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Here are the categories of gases:

  • Ideal Gas

  • Non-ideal Gas (real gas)

The table given below shows the properties of gases:



SI units












mm Hg

Quantity of Gas



Behaviour of Gas Molecules

The behavior of gas molecules are as follows:

  1. Volume (V)

  2. Temperature (T)

  3. Quantity (n)

  4. Pressure (P)

The factors mentioned above are related to each other. Some of these factors are given below:

  1. The volume of the gas increases due to an expansion of gas molecules due to a rise in temperature.

  2. The volume of the gas drops due to the contraction of gas molecules and the decline in temperature.

  3. The pressure of the gas rises due to an expansion of gas molecules because of the rise in temperature.

  4. The gas pressure drops because of the contraction of gas molecules because of the decrease in temperature.

  5. The temperature of the gas molecule should be low enough, or the pressure of the gas must be very high when we convert the gas either into solid or liquid.

  6. The pressure of the gas will either increase or decrease depending on the increase or decrease of pressure, respectively.

  7. When the pressure decreases, both the quantity and volume of the gas decrease.

  8. The rise in quantity and volume of the gas is noticed when its pressure increases.

What are Gases made of?

Gas is called the third fundamental states of matter. Pure gas is created from the individual atoms like neon (a noble gas). Gas like oxygen is made from a single type of atom.

What is Real Gas?

A real gas comes under the category of non-ideal gases. The molecules of real gas occupy space and interact with each other. A real gas doesn’t follow the ideal gas laws.

What is Flue Gas?

Flue gas is a gas that exists in the atmosphere as a result of a flue. The flue gases are formed into the atmosphere due to the release of the gas from the furnace, oven, broiler, fireplace, etc. through a channel.

What is an Ideal Gas?

An ideal gas is a theoretical aspect. It is believed that an ideal gas is the composition of many randomly moving point particles. These particles undergo inter-particle interactions.

The formula for an ideal gas is the product of pressure and volume of a one-gram molecule of an ideal gas is the same as the product of a universal gas constant, absolute temperature, and the number of moles of the gas.

To know what is the ideal gas constant, the mathematical expression is:

PV = nRT = NkT


  • P = Pressure of the gas

  • V = Volume of the gas

  • n = Number of moles

  • R = Universal gas constant = 8.3145 J. mol-1. K-1

  • T = Temperature of the gas

  • N = Avogadro’s number (NA = 6.0221 × 1023)

What are the Ideal Gas Laws?

The combination of three gas laws gives rise to the ideal gas law. The formula for an ideal gas is given above:

We can derive ideal gas laws from the following laws:

  1. Boyle’s law

Boyle states that the pressure (P) of the gas is inversely proportional to its volume (V) at a constant temperature.

P ∝ \[\frac{1}{V}\]

  1. Charles’s Law

Charles states that at a fixed mass of a gas, its volume (V) is directly proportional to the temperature (T).

V ∝ T

  1. Avogadro’s Law

At constant pressure, & temperature, the volume (V) of the gas and number (n) of moles are directly proportional to each other. 

 V ∝ n 

or, \[\frac{V}{n}\] = k (k is a constant)

What are the Different States of Matter?

According to research, we found four states of matter; they are listed as: 

  1. Solids

  2. Liquids

  3. Gases

  4. Plasma

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FAQ (Frequently Asked Questions)

Q1. Calculate the total volume occupied by the carbon dioxide gas having a mass of 2.34 grams at STP.

Ans: We need to consider the formula for the ideal gas law for calculating the volume.

The formula is:

V = nRT/P

By putting all the values from the above formula, we get:

V = [(2.34g/44g.mol-1) * (0.08206L atm mol-1 K-1)* (273.0K)] / 1.00 atm 

Volume, V = 1.19 L

Q2. What are the assumptions made for the ideal Gas Law?

Ans: Here are the assumptions for the ideal gas law:

  1. The volume of the particles is negligible, as they are very small.

  2. There is no interaction between particles.

  3. Absence of repulsive or attractive forces.

  4. The temperature of the gas and its average kinetic energy are directly related.

Q3. State and explain the fourth state of Matter.

Ans: The fourth state of matter is known as plasma. It has its recognition along with solid, liquid, and gas. It is generated from the heating of gas and contains a mixture of ions and electrons.

Q4. Who discovered the Plasma state? What type of Matter is it?

Ans: Plasma was discovered by the physicist Sir William Crookes. He identified the plasma in a Crookes tube. Also, he named it as a radiant matter.