Postulates of kinetic theory of gases

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

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

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.

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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

Below are the physical properties of metals:

  1. They exist in solid state.

  2. The have high densities.

  3. They are good conductors of heat and electricity.

  4. The have the ability to be polished, to glow, sparkle and reflect light.

  5. They can be bent, flattened and made into sheets called foils.

  6. They can be drawn into wires.

  7. Iron undergoes magnetism while most metals are poorly magnetized.

  8. They typical have high melting point.

  9. They generally have high boiling point.

  10. With the exception of lithium, sodium and potassium, most metals are generally hard.

  11. They have the ability to make sound when in contact with other objects or metals.

  12. Please read details on the physical properties of metals here

John Dalton is an English chemist who brought clarity into the composition of matter and the basis for their chemical reactions.

Below are Dalton's Atomic Theory:

  1. All matter consists of tiny indivisible particles called atoms.

  2. Atoms of the same element are identical to each other in every aspect because they have the same shape and mass, while atoms of different elements are different in all respect.

  3. Atoms are indestructible and can neither be created nor destroyed.

  4. Atoms of different elements can combine with each other in simple whole number ratios to form compounds.

  5. Atoms of the same element share similar physical and chemical properties. They can also combine in more than one ratio to form two or more compounds.

Meanwhile, understand that the above theories of John Dalton had been modified.

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

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.