Summary on the kinetic molecular theory of gases

len Alfred Ajibola - 15th December, 2022 @ 08:06 PM

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

Postulates of the kinetic molecular theory of gases:

The kinetic molecular theory of gases (KMT), or simply referred to as the kinetic theory of gases, was established in the 19th century by the great works of James Clerk Maxwell (a British scientist) and Ludwig Boltzmann (an Austrian physicist) during their respective studies on gaseous behavioral pattern.

These behavioral patterns of gaseous molecules are explained in terms of pressure, temperature, viscosity, thermal conductivity and volume through their constant, random and linear motion at room temperature. Examples of gaseous molecules include oxygen (O2), chlorine (Cl2) and carbon(IV)oxide (CO2) respectively.

Please read on the gaseous state of matter here.


The postulates of the kinetic theory of gases simply refers to the basic principles of gaseous behaviours. This behavior can be properly studied when the gas particles are contained; (that is, the gas particles are present inside a sealed container). See the image below:

Gas molecules in a sealed container - Len Academy

Meanwhile, understand that the use of a sealed or closed container is important due to the constant motion of gases at room temperature. In this regard, the gas molecules will move, diffuse and disappear into the atmosphere if not contained.

Please read on diffusion with worked example here.


The behavioral patterns and characteristics of gas molecules are summarized in their constant random motion, particles collision, occupied volume, particles size, closeness of particles and kinetic energy generated by these particles. In this regard, the five basic postulates of the kinetic theory of gases are listed below:

  1. Gas molecules move randomly in a straight line.

  2. The collision between the gas molecules are perfectly elastic.

  3. The actual volume occupied by each gas molecule is neglible.

  4. The cohesive forces between the gas molecules are neglible.

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

You can read a detailed explanation on these postulates of kinetic theory of gases here.


With regards to the kinetic theory of gases (as listed above), important facts can be deduced. These deductions have proven to be useful in our world today. As an instance, helium (He) is preferred in the filling of balloons due to its light weight (mass), unlike carbon(IV)oxide (CO2) which is heavier in mass. However, the latter (CO2) is applied in soft drinks since it is readily absorbed into the liquid (soft drinks and soda), thus forming tiny bubbles in it.

Please read on molecular mass alongside its calculations here.


A good knowledge on the kinetic theory of gases will aid students in understanding various laws of chemistry. This include Boyle's law, Charles' law, Gay-Lussac's law of combining volumes, Dalton's law of partial pressure, Graham's law of diffusion and Avogadro's law.

Please read on the mole concept and Avogadro's number here.


From the above explanations so far, below is an overall summary on the kinetic theory of gases:

  • All gases are made up of tiny molecules that are constantly, randomly and persistently moving in straight lines.

  • All the molecules in an ideal gas obey Newton's laws of motion.
    Please read on motion and speed here.

  • The separation (distance) between the gaseous molecules are overwhelmingly greater than the size of each molecule.

  • Collisions between the gas molecules themselves and the walls of the container are considered to be perfectly elastic.

  • Compared to the space present inside the container, the size of the gas molecules are very small or neglible.

  • If a gas sample is kept in a container, the molecules making up the gas will not exert any force on the walls of the container during collision.
    Please read on states of matter and characteristics of solid here.

  • The time interval of a collision between two molecules, and between a molecule and the walls of the container is considered to be neglible.

  • If a gas sample is left for a sufficient time, it will eventually come to a steady state. In this case, the density of molecules and their distributions are independent of position, distance and time.

  • The average kinetic energy of the gaseous molecules is temperature dependent and will always be in proportion to it.

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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