Summary on the kinetic molecular theory of gases

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

Topics in Chemistry

Gas laws in chemistry Charles's law explained Calculation questions on Charles's law Examples of Charles's law in real life Boyle's law explained Calculation questions on Boyle's law Examples of Boyle's law in real life 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

Academic Questions in Chemistry

Please click here to see all Questions and Answers

With regards to redox reactions, which of the following statement is wrong?

  • A. Redox reaction are examples of chemical change

  • B. Reduction is the gain of electron

  • C. Substances that donates election during chemical reaction are termed reductants

  • D. Oxidizing agents are always reduced in chemical reactions

  • E. Oxidation occurs at the cathode in electrolysis

  • F. Hydrogen is a reducing agent

In chemistry, physical change is associated only with the rearrangement of molecules while the internal composition of the substance remains the same.

  • A. True

  • B. False

_____ electron(s) is a term that describes the number of electron(s) in the outermost shell of an atom.

  • A. Outer

  • B. Excess

  • C. Valence

  • D. Positive

  • E. Negative

  • F. Last

_____ is the negative electrode in electrolysis.

  • A. Anode

  • B. Anion

  • C. Cathode

  • D. Cation

  • E. Ion

  • F. Electrolyte

Electrovalent Bond - Len Academy

The above diagram shows the _____ type of bond.

  • A. Covalent

  • B. Polar covalent

  • C. Coordinate covalent

  • D. Metallic

  • E. Van dear walls

  • F. Ionic

 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

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

Notable points in Chemistry

Periodic Table - Len Academy

The periodic table, also called periodic table of elements or Mendeleev's table, is a table that shows an organized arrangement of the 118 chemical elements according to their atomic number.

Out of the 118 elements; elements 1 - 94 are present in nature while elements 95 - 118 are synthesized artificially.

The manner at which elements are arranged on this table reveals some similarities in their electronic configurations and chemical properties.

Please read on the periodic table of elements here.

A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)

  • Solution:

Step 1: Identify the given parameter from the question.

  • Fe = 69.94%,   O = 30.06%.

  • Empirical formula = Fe?O?


Step 2: Convert the percentages to gram. (just attribute grams to the %).

  • 69.94% = 69.94g while 30.06% = 30.06g


Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in emperical formula.

  • Mole of Fe: 69.94/55.85 = 1.252mol

  • Mole of O: 30.06/16 = 1.879mol


Step 4: Divide both sides by the smallest mole ratio.

  • Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1,    1.879/1.252 = 1.5

  • We now have the formula = Fe1O1.5


Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number '2' is the smallest whole number that will make '1.5' and '1' whole numbers when multiplied by it.

  • For iron (Fe), we will have 1 x 2 = 2

  • For oxygen (O), we will have 1.5 x 2 = 3


Step 6: Write the empirical formula.

  • The empirical formula= Fe2O3

  • Iron(III)tetraoxosulphate(VI)

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.