Postulates of kinetic theory of gases

len Alfred Ajibola - 12th December, 2022 @ 08:24 AM

Topics in Chemistry

Summary on the kinetic molecular theory of gases Postulates of kinetic theory of gases Avogadro's number explained with worked examples Mole and Avogadro's Number explained Le Chatelier's Principle: Changes in concentration and pressure in dynamic equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures What are mixtures? Characteristics of mixtures Physical properties of matter Chemical properties of matter explained with examples Differences between physical and chemical change in chemistry Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid state of matter: Characteristics of liquids

Academic Questions in Chemistry

Please click here to see all Questions and Answers

 Metals are referred to as _____ in their impure state.

  • A. Diluted

  • B. Consecrated

  • C. Coloured

  • D. Ores

  • E. Stained

  • F. Strained

Metals generally have the quality to shine, glow, sparkle, glitter, reflect light and be polished. This characteristic of metals is termed _____.

  • A. State

  • B. Ductility

  • C. Luster

  • D. Malleability

  • E. Hardness

  • F. Inflorescence

The _____ spectrometry experiment conducted on isotopic elements gave a confirmation for the existence of isotopes.

  • A. Mole

  • B. Volume

  • C. Weight

  • D. Number of moles

  • E. Mass

  • F. Amount of substance

John Dalton's first atomic theory was modified based on a discovery made by _____.

  • A. Sir Isaac Newton

  • B. Albert Einstein

  • C. Avogadro

  • D. Rutherford

  • E. Boyle and Charles

  • F. Gay Lussac

Which of the following isn't an element of the periodic table.

  • A. J

  • B. Y

  • C. W

  • D. B

  • E. U

  • F. K

According to the periodic table, elements in the same group have got the same number of shells.

  • A. True

  • B. False

The periodic table of elements is also called the Mendeleev's table.

  • A. True

  • B. False

The simplest formula of a compound is termed _____.

  • A. Emperical formula

  • B. Molecular formula

  • C. Avogadro's number

  • D. Mass formula

  • E. Molar mass formula

  • F. Mole ratio

Kinetic Theory of Gases:

An understanding on the concept of the kinetic theory of gases is considered a vital part of chemistry. This is true because chemistry involves the study of matter and the changes they undergo. In this regard, gaseous particles are always in motion (moving). In fact, the word kinetic means 'in motion'.

Take for instance, when a perfume is released into a room, the gaseous particles of the perfume will diffuse around the room. By diffusion, I mean that the gaseous particles of the perfume will move from the region of higher concentration to that of lower concentration around the room. As a result, the entire room will become filed with the scents of the perfume, and this is a function of the random motion exhibited by gaseous particles.

Please read on the characteristics gases here.


It is noteworthy to state that gases are comprised of a large number of separated submicroscopic particles at the atomic and molecular levels. According to the kinetic theory of gases, these extremely small gaseous particles are always in a constant, rapid and random motion which occurs in a straight line. While in motion, the gaseous particles will constantly collide with one another and the walls of its container.

In the 19th century, the kinetic theory of gases was established by the great works of British scientist - James Clerk Maxwell and Austrian physicist - Ludwig Boltzmann, in an attempt to study their behaviors.


The kinetic theory of gases further explains how properties like pressure, temperature, viscosity, thermal conductivity and volume impact on the movement of various gaseous molecules.

You can read on Dalton's atomic theory and its modifications here.


The basic principles of kinetic theory of gases may also be termed as the postulate of the kinetic theory of gases. They are listed and explained below:


1. Gas molecules move randomly in a straight line

Gaseous molecules present in a container are not static. They are in constant motion. In fact, if the container is opened, the gases will escape (or move out) from it. For this reason, we see why released gases escape into an open space. This random movement in a straight line is a major characteristic of gases since their comprising atoms or molecules are extremely small and widely separated.

Also, the forces that tend to attract the gaseous particles are very small or neglible. In summary, gas molecules are constantly and randomly moving in a straight line. This is in support of Newton's first law of motion.

Please read on Newton's laws of motion here.

With regards to gaseous molecules as material bodies, they obey Newton's laws of motion. This means that the molecules of an ideal gas will move randomly in straight lines until they collide with each other or with the walls of the container. This is shown in the image below:

Kinetic theory of gases - Lenacad


2. The collision between gas molecules are perfectly elastic

Whenever gas molecules collide or come into contact with one another, they do so in an elastic manner. This implies that the colliding gaseous molecules bounce off one another, changing their directions and kinetic energies in the process.

Meanwhile, understand that gas molecules do not adhere to each other when they collide. This is also true whenever they collide with the walls of the container. In a similar fashion, they bounce off the container and do not stick to it.

Collisions are perfectly elastic with gaseous molecules. Whenever two gas particles collide, they change their directions and kinetic energies, but the total kinetic energy is conserved. Collisions are not sticky.

You can read on periodic table and classification of elements here.


3. The actual volume occupied by the gas molecules are neglible

Each particle or atom that make up a gas is very small (microscopic). Also, they are widely separated from other gaseous particles.

Focusing on this particle, the actual volume it occupies in the container is extremely small (or even neglible). For this reason, the particles can freely move and collide since there exist a massive space within the container.

It is noteworthy to state that gas particles are separated by a large distance in relation to their particulate size. In this regard, if the container was opened, the gaseous particles will escape completely because of the massive space in the atmosphere.

You can read on the functions of the atmosphere here.

In summary, the average distances of the gaseous particles are much greater than the sizes of the particles themselves.

You can attempt various questions in chemistry here.


4. The cohesive forces between the gas molecules are neglible

As explained earlier, gas molecules are constantly in motion and will always collide with themselves and the walls of the container. However, there is no interactive force (that is, force of attraction or repulsion) between the gaseous particles.

Recall that solids have their particles adhering closely to one another. In fact, this is why solids have definite shapes and fixed sizes with static particles. In other words, the cohesive forces in solids are great. This is not the case in gases.

You can read more on the states of matter and characteristics of solids here.

With regards to gases, the particles are widely spaced apart and are also constantly moving. Based of this fact, gases have no definite shape since there is no cohesive or binding forces between its particles.


5. The average kinetic energy of the gas molecules is directly proportional to the absolute temperature

The term 'average' is very significant in this theory. Now, let's imagine a gas is present inside a sealed metallic container. Based on our previous kinetic theories, the gaseous molecules will be in constant motion within the container, giving rise to an average kinetic energy of the overall gas molecules. Meanwhile, recall that the word 'kinetic' means moving or in motion.

Now, let's imagine that heat is applied to this container. When this happens, the gases will move at an increased speed (motion) and collision will be consequently increased. In short, a higher temperature will imply a higher speed and collision between the gas molecules themselves, alongside the gas molecules and the container's walls. The reverse will happen if temperature is decreased by putting the container in a refrigerator. In fact, at an absolute zero temperature, the gaseous particles will cease moving.

Please read more on heat and temperature here.

Need more answers to this topic? Please enter your search below:

Kindly share this article via the links below:


Please contact Alfred via the above whatsapp link for a comprehensive online academic coaching in Biology, Chemistry, Basic Science and ICT

Click here to read the amazing features of the Len Academy Smart School Software. However, contact Alfred through the above whatsapp link if you require a standard website for your business or school at an affordable price

Please click here to follow Len Academy on Google News.

Please like and follow our official facebook page here for great educational write-ups.

You can follow Len Academy on twitter here.Thank you.

Please Register here or Login here to contribute to this topic by commenting in the box below.

Amazing facts in Chemistry

Plastic and Glass can decompose, but not in our lifetimes. It takes an average time of 450 years for plastics to decompose. As for the decomposition of glasses, it takes about 4,000 years

The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals.

Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools

Water freezes faster when it’s warm than when it’s cold

Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy

If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.

Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre


In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.

Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:

  1. Alkanes

  2. Alkenes

  3. Alkynes

They are shown in the image below:

Alkanes, Alkenes and Alkynes - Len Academy

It's important to note the followings:

  • Alkanes have single bonds (only) in their structures.

  • Alkenes always have a carbon-carbon double bond present in their structure.

  • Alkynes always have a carbon-carbon triple bond present in their structure.


Aromatic hydrocarbons are classified into:

  • Arenes: They contain benzene ring as a structural unit. Below is the structure of a benzene ring.

Benzene Ring - Len Academy


  • Nonbenzenoid aromatic hydrocarbons: They possess special stability but lack a benzene ring as a structural unit.

Organic chemistry is the study of carbon and it's compounds.

Carbon is the focus of organic chemistry because it has a wide chemical diversity in the sense that it can combine with other carbon atoms to form a long chain of carbon molecule. This ability and process whereby carbon can form a long chain of itself is called catenation.

Please read the introduction to organic chemistry here

A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.

Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.

The large molecules (above) have no specific chemical formula throughout their volume.

Please read more on carbohydrates and sugars here

Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the modifications of Dalton's atomic theory.

Please read on Dalton's atomic theory and its modifications here.

Calculate the Relative Molecular Mass of methane (CH4). (Carbon=12.001 and H=1.00794)

  • Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen

  • Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.

  • 12.001 + (1.00794 x 4)

Molecular Mass of Methane = 16.033 amu

Please read more on molecular mass here

Calculate the Relative Molecular Mass of water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)

  • Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen

  • Water contains 2 atoms of Hydrogen and 1 atom of oxygen.

  • (1.00794 x 2) + 15.9994

Molecular Mass of Water = 18.015 Da

Please read on emperical formula and its calculations here

Gold - Len Academy

Below are some facts about gold:

  • It is the only metal that has a gold (golden) color

  • Gold is present inside the earth crust in all the seven continents

  • Pure gold is soft and very stretchable (It can even be stretched into threads)

  • The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'

  • Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables

  • Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants

  • The term Gold originated from an ancient English word 'geolu' which means yellow

  • 24karat gold is the purest gold element

Please read more interesting facts about gold here