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Chapter 13 – Kinetic Theory

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:


The kinetic theory holds paramount importance in physics. Various concepts come under this head. Kinetic theory is one of the most accepted and successful theories of gas. The topics are easier once you understand them. We hope this article helps you understand the concepts, and you can revise for your exam with these notes.

There are three theories of the molecular nature of matter:-

  • Dalton’s Theory

This theory simply says matter in the universe, is made up of small particles called an atom. These atoms cannot be destroyed or created. All the properties of these atoms are the same. 

  • Avagadro’s Law

As per this law, the number of gases has an equal number of molecules if they have the same volume at equal, pressure and temperature. 

  • Gay Lussac’s Law

According to this law, the pressure of a given amount of gas varies directly to its temperature if the volume of a gas is taken as constant.

The behaviour of gases depends upon various properties like temperature, volume, etc. and laws followed by the molecules of gas. 

Factors Affecting the Behavior of Gases

  • Temperature – As there is an expansion of gas molecules, the volume of the gas increases and temperature also increases simultaneously.
  • Volume –  As there is an expansion of gas molecules, the pressure of the gas increases and temperature also increases simultaneously.
  • Pressure – The temperature of gas should be low to convert gas into solid or liquid.
  • Quantity – The volume and quantity, of the gas, must be less for pressure to decrease and vice versa.

The kinetic theory of gases explains the three macroscopic properties of the gas in terms of the microscopic nature of atoms and molecules. It mainly describes the molecular composition of the gas. It further states that due to particles colliding with each other as the gas pressure arises. This theory helps in developing a correlation between the microscopic phenomenon.

Assumptions of the Kinetic theory of Gases

  • Gas is a collection of a huge number of atoms or molecules.
  •  The atoms are very small in size like a dot which made up the gas.
  • It has negligible volume particles.
  • The parties do not, any interaction among them as they are independent.
  • As there is a lack of interaction among parties. As a result, these particles are always in constant motion.
  • The collisions are elastic in nature.

This law states that total energy is equally distributed, in all possible energy modes and each mode having average energy equal to ½.

In order to study thermodynamics, a specific property was required, which has no dependence on the quantity or size of the matter. As it is independent of the quantity or size of the matter, this made it a concentrated property. In other words, it can be defined as the amount of heat required to raise a temperature by one-degree celsius of a unit mass of that substance. It can be mathematically shown as:-


Q – Amount of heat required

M – To change the temperature

s – Specific heat capacity

ΔT – Substance

If you take a  system of agitated particles, the average distance travelled by a moving particle which results in a change in their energy or physical properties is the mean free path. 

Factor affecting the mean free path

  • The molecules come closer to each other as the density increases. They result in decreasing the mean free path and increasing the number of collisions. 
  • The mean free path decreases as the number of molecules increases, and the probability of collision increases.
  • The space between the molecules decreases as the radius of the molecule increases. It leads to an increase in the number of collisions and decreasing the mean free path.
  • The density of the gas is also affected by the pressure, temperature, and other physical factors.

It describes the behaviour of gasses. This theory is based upon various postulates such as size, the motion of a particle of gas, and their interaction with the molecules.

1. What does the kinetic theory explain?

Answer. A universal theory of matter which in terms of the motion of atoms and molecules, explains the physical properties. The properties such as pressure and temperature in kinetic theory are viewed as the statistical properties of a large number of particles.

2. What are the 3 assumptions of the kinetic theory?

Answer. The three assumptions of the kinetic theory are:

  • The gas is composed of a large number of identical molecules, and they are separated by distances moving in random directions. 
  • The molecules do not interact but undergo perfectly elastic collisions with each other.
  • The heat is the transfer of kinetic energy between molecules.

3. What is the kinetic theory of heat?

Answer. It simply, means that the average kinetic energy of its parties determines the temperature of a body. The energy increases with the inflow of heat.

4. What is the kinetic theory useful for?

Answer. This theory assisted in understanding the governing equations of gas dynamics and notation of classical mechanics came into existence because of this theory.

Kinetic theory is one of the important topics of physics and the most crucial concept from the point of view of your exam. We help you understand Kinetic theory first, with in-depth concept notes and explanatory video on the MSVgo app. The MSVgo philosophy is to enable a core understanding of any concept. The video library of the MSVgo app explains concepts with examples or explanatory visualisations or animations. It helps you learn and prepare for the exam, happy learning.

High School Physics

  • Alternating Current
  • Atoms
  • Communication Systems
  • Current Electricity
  • Dual nature of Radiation and Matter
  • Electric Charges and Fields
  • Electricity
  • Electromagnetic Induction
  • Electromagnetic Waves
  • Electron Beams and Radioactivity
  • Electrons and Photons
  • Electrostatic Potential and Capacitance
  • Fluid Pressure
  • Force and Acceleration
  • Force And Laws Of Motion
  • Gravitation
  • Internal Energy
  • Kinetic Theory
  • Law of motion
  • Light – Reflection And Refraction
  • Magnetic Effects Of Electric Current
  • Magnetism and Matter
  • Management Of Natural Resources
  • Mechanical properties of Fluids
  • Mechanical properties of Solids
  • Motion
  • Motion in a plane
  • Motion in a straight line
  • Moving Charges and Magnetism
  • Nuclear Energy
  • Nuclei
  • Oscillations
  • Our Environment
  • Paths of Heat
  • Physical world
  • Ray optics and optical instruments
  • Semiconductor Devices
  • Semiconductor Electronics: Materials, Devices and Simple Circuits
  • Simple Machines
  • Sound
  • Sources Of Energy
  • Specific and Latent Heats
  • Spherical Mirrors
  • Static Electricity
  • Systems of Particles and Rotational motion
  • Thermal properties of matter
  • Thermodynamics
  • Units and Measurement
  • Vectors, Scalar Quantities and Elementary Calculus
  • Wave Optics
  • Waves
  • Work, Power and Energy

High School Chemistry

  • Acids, Bases and Salts
  • Alcohols, Phenols and Ethers
  • Aldehydes, Ketones and Carboxylic Acids
  • Aliphatic and Aromatic Hydrocarbons
  • Alkyl and Aryl Halides
  • Amines
  • Analytical Chemistry 
  • Atomic Structure
  • Atoms And Molecules
  • Basic concepts of Chemistry
  • Biomolecules
  • Carbon And Its Compounds
  • Carboxylic acids and Acid Derivatives
  • Chemical Bonding and Molecular Structures
  • Chemical Energetics
  • Chemical Equilibria
  • Chemical Kinetics
  • Chemical Reactions And Equations
  • Chemical Reactions and Their Mechanisms
  • Chemistry in Everyday Life
  • Chemistry of p-Block elements
  • Chemistry of Transition and Inner Transition
  • Classification of Elements
  • Coordination Compounds
  • Cyanide, Isocyanide, Nitro compounds and Amines
  • Electrochemistry
  • Electrolysis
  • Elements, Compounds and Mixtures
  • Environmental Chemistry
  • Equilibrium
  • Ethers and Carbonyl compounds
  • Haloalkanes and Haloarenes
  • Hydrocarbons
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  • Ideal solutions
  • Introduction to Organic Chemistry
  • Ionic equilibria
  • Matter
  • Matter Around Us
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  • Mole Concept and Stoichiometry
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  • Organic Chemistry – Basic Principles
  • Periodic Classification of Elements
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  • Polymers
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  • Principles and Processes of Isolation of Elements
  • Redox Reactions
  • Relative Molecular Mass and Mole
  • States of Matter
  • Structure Of The Atom
  • Study of Compounds
  • Study of Gas Laws
  • Study of Representative Elements
  • Surface Chemistry
  • The d-block and f-block elements
  • The Gaseous State
  • The p-Block Elements
  • The Periodic Table
  • The s-Block Elements
  • The Solid State
  • Thermodynamics

High School Biology

  • Absorption and Movement of Water in Plants
  • Adolescent Issues
  • Anatomy of Flowering Plants
  • Animal Kingdom
  • Bacteria and Fungi-Friends and Foe
  • Biodiversity and Conservation
  • Biofertilizers
  • Biological Classification
  • Biomedical Engineering
  • Biomolecules
  • Biotechnology and its Applications
  • Biotic Community
  • Body Fluids and Circulation
  • Breathing and Exchange of Gases
  • Cell – Unit of Life
  • Cell Cycle and Cell Division
  • Cell Division and Structure of Chromosomes
  • Cell Reproduction
  • Cellular Respiration
  • Chemical Coordination and Integration
  • Circulation
  • Control And Coordination
  • Crop Improvement
  • Digestion and Absorption
  • Diversity In Living Organisms
  • Ecosystem
  • Environmental Issues
  • Excretory Products and their Elimination
  • Flowering Plants
  • Genes and Chromosomes
  • Health and Diseases
  • Health and Its Significance
  • Heredity And Evolution
  • Heredity and Variation
  • How Do Organisms Reproduce?
  • Human Diseases
  • Human Eye And Colourful World
  • Human Health and Disease
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  • Hygiene
  • Improvement In Food Resources
  • Integumentary System- Skin
  • Kingdom Fungi
  • Kingdom Monera
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  • Life Processes
  • Locomotion and Movement
  • Microbes in Human Welfare
  • Mineral Nutrition
  • Molecular Basis of Inheritance
  • Morphology of Flowering Plants
  • Neural Control And Coordination
  • Nutrition in Human Beings
  • Organism and Population
  • Photosynthesis
  • Photosynthesis in Higher Plants
  • Plant Growth and Development
  • Plant Kingdom
  • Pollination and Fertilization
  • Pollution; Sources and its effects
  • Principles of Inheritance and Variation
  • Reproduction and Development in Angiosperms
  • Reproduction in Organisms
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  • Respiration in Human Beings
  • Respiration in Plants
  • Respiratory System
  • Sexual Reproduction in Flowering Plants
  • Strategies for Enhancement in Food Production
  • Structural Organisation in Animals
  • Structural Organisation of the Cell
  • The Endocrine System
  • The Fundamental Unit Of Life
  • The Living World
  • The Nervous System and Sense Organs
  • Tissues
  • Transpiration
  • Transport in Plants

High School Math

  • Algebra – Arithmatic Progressions
  • Algebra – Complex Numbers and Quadratic Equations
  • Algebra – Linear Inequalities
  • Algebra – Pair of Linear Equations in Two Variables
  • Algebra – Polynomials
  • Algebra – Principle of Mathematical Induction
  • Algebra – Quadratic Equations
  • Binomial Theorem
  • Calculus – Applications of Derivatives
  • Calculus – Applications of the Integrals
  • Calculus – Continuity and Differentiability
  • Calculus – Differential Equations
  • Calculus – Integrals
  • Geometry – Area
  • Geometry – Circles
  • Geometry – Conic Sections
  • Geometry – Constructions
  • Geometry – Introduction to Euclid’s Geometry
  • Geometry – Three-dimensional Geometry
  • Geometry – Lines and Angles
  • Geometry – Quadrilaterals
  • Geometry – Straight Lines
  • Geometry – Triangles
  • Linear Programming
  • Matrices and Determinants
  • Mensuration – Areas
  • Mensuration – Surface Areas and Volumes
  • Number Systems
  • Number Systems – Real Numbers
  • Permutations and Combinations
  • Probability
  • Sequence and Series
  • Sets and Functions
  • Statistics 
  • Trignometry – Height and Distance
  • Trignometry – Identities
  • Trignometry – Introduction

Middle School Science

  • Acids, Bases And Salts
  • Air and Its Constituents
  • Basic Biology
  • Body Movements
  • Carbon and Its Compounds
  • Cell – Structure And Functions
  • Changes Around Us
  • Chemical Effects Of Electric Current
  • Chemistry in Your Life
  • Coal And Petroleum
  • Combustion And Flame
  • Components Of Food
  • Conservation Of Plants And Animals
  • Crop Production And Management
  • Electric Current And Its Effects
  • Electricity And Circuits
  • Elements and Compounds
  • Fibre To Fabric
  • Food production and management
  • Force And Pressure
  • Forests: Our Lifeline
  • Friction
  • Fun With Magnets
  • Garbage In, Garbage Out
  • Getting To Know Plants
  • Health and Hygiene
  • Heat
  • Hydrogen
  • Life Processes: Nutrition in Animals and Plants
  • Light, Shadows And Reflections
  • Materials: Metals And Non-Metals
  • Matter and Its States
  • Metals and Non-metals
  • Micro Organisms: Friend And Foe
  • Motion And Measurement Of Distances
  • Motion And Time
  • Nutrition In Animals
  • Nutrition In Plants
  • Organization in Living Things
  • Our Environment
  • Physical And Chemical Changes
  • Pollution and conservation
  • Pollution Of Air And Water
  • Reaching The Age Of Adolescence
  • Reproduction In Animals
  • Reproduction In Plants
  • Respiration In Organisms
  • Rocks and Minerals
  • Separation Of Substances
  • Simple Machines
  • Soil
  • Some Natural Phenomena
  • Sorting Materials Into Groups
  • Sound
  • Stars And The Solar System
  • Structure of Atom
  • Synthetic Fibers And Plastics
  • The Living Organisms And Their Surroundings
  • Transfer of Heat
  • Transformation of Substances
  • Transportation In Animals And Plants
  • Universe
  • Waste-water Story
  • Water: A Precious Resource
  • Weather, Climate And Adaptations Of Animals To Climate
  • Winds, Storms And Cyclones

Middle School Math

  • Addition
  • Area and Its Boundary
  • Boxes and Sketches
  • Data Handling
  • Fun With Numbers
  • Heavy and Light
  • How Many
  • Long And Short
  • Mapping
  • Measurement
  • Money
  • Multiplication and Factors
  • Multiply and Divide
  • Numbers
  • Parts and Wholes
  • Pattern Recognition
  • Patterns
  • Play With Patterns
  • Rupees And Paise
  • Shapes And Angles
  • Shapes And Designs
  • Shapes and Space
  • Similarity
  • Smart Charts
  • Squares
  • Subtraction
  • Tables And Shares
  • Tenths and Hundredths
  • Time
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