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Chapter 12 – Thermodynamics

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


Thermodynamics is an essential branch of physics, which explains the properties of heat, work, and temperature. You need to study it thoroughly to score good marks in your exams. Thermodynamics is a wide field of physics of immense value. With this article, you will gain a complete overview of thermodynamics that will help you revise the topic at a later stage.

Kinetic theory expresses that the behaviour of gases relies upon the idea that gases have free particles and atoms. In solids, particles are firmly stuffed; in fluids, atoms are less firmly pressed; and in gases, atoms are isolated with no proper arrangement. 

Kinetic theory is widely acknowledged as a successful theory. It explains the behaviour of molecules. A molecule is a tiny unit that has the same property as a sample. The kinetic theory of gases explains how molecules affect gas characteristics like temperature and pressure.

As per many scientists, everything in this world is made up of atoms. Dalton’s atomic theory conveys the idea that all matter is made up of atoms that are indivisible. Even atoms present in each element are analogous in mass and properties. Gay-Lussac’s Law asserts that when the temperature of the gas is elevated, its pressure also rises proportionally.  This is known as the molecular nature of matter.

The behaviour of gases states that gases are continuously moving and colliding with each other. It establishes a relationship between volume, pressure, and temperature of a gas. It can be expressed as PV = NRT, where P is the pressure, V is the volume, N is the number of moles of gas, R is the universal gas constant, and T is the absolute temperature. It states that there is no force of attraction between the gases.

According to the kinetic theory of an ideal gas, one gram molecule of an ideal gas is equal to the product of a number of moles of the gas, universal gas constant, and absolute. It represents PV= nRT = NkT, where, P – Pressure, V- Volume, n – Number of moles, R – Universal gas constant, T – Temperature, and N- Avogadro’s number. Any gas that satisfies this equation is called an ideal gas.

For any system in the dynamic setup in thermal equilibrium, the total energy is allocated equally among the degree of freedom.  Degrees of freedom mean independent displacement or rotation that orient the part of the system. In case molecules are free in space, it acquires translational degrees of freedom as three coordinates need to be defined. Similarly, in the triatomic molecule, the degree of freedom is 6 as per molecule of gas, represented by –

Translational degrees of freedom are present only in monatomic gases. Each degree of freedom constitutes ½ kg. Rigid diatomic gases have both translational and rotational degrees of freedom, but the vibrational degree is absent. They have a rigid oscillator, and non-rigid have all degrees of freedom, which are translational, rotational, and vibrational. This concept is called specific heat capacity.

In the case of polyatomic gases, there are 4 translational, 4 rotational, and ‘f’ numbers of vibrational degrees of freedom. In a nutshell, specific heat is calculated on the basis of freedom that is independent of temperature.  All substances have specific heat shows zero as T->0

The average distance between two collisions is called the mean free path. Since molecules in a gas are loosely packed, it means that it can move freely and collide with each other. The distance at which gases travel without colliding with each other is called a mean free path. 


Formula – λ (N/V) π r2 ≈ 1, where r is the radius of a molecule.

 This gives:  λ = 1 / [(N/V) π r2]

Numerical estimates:- 

Molecular cross-sectional area:  π r2 ≈ 10-19 m2

Molecular density (sea level): N/V = P/kT ≈ 3 x 1025 molecules/m3

Mean free path (sea level): 10-7m ≈ hundreds of molecular diameters

Kinetic molecular theory studies the macroscopic properties of gases and helps in a better understanding of gas laws. It explains that gas particles manifest perfectly elastic collisions. 

Charles’ and Boyle’s Laws can be expounded with the help of the kinetic molecular theory. Collison produced by gases is elastic in nature, and when these molecules merge, kinetic energy is conserved.

What does the kinetic theory explain?

Kinetic theory explains the following –

  1. It explains the molecular interpretation.
  2. It remains consistent with Avogadro’s hypothesis and gas laws.
  3. It adequately comprehends the heat capacities of many gases.

What are the three assumptions of the kinetic theory?

The assumptions are –

  1. Molecules or atoms don’t correspond with each other.
  2. Intermolecular force is absent in ideal gases.
  3. Kinetic energy will be conserved.

What is the kinetic theory of heat?

The kinetic theory of heat implies that the temperature of the body is controlled through the kinetic energy of particles and the incursion of warmth raises the energy.

What is the kinetic theory useful for?

Kinetic theory can be useful in the following ways – 

  1. It helps to explain why matter exists and how it changes from one phase to another.
  2. It helps in the understanding of other properties of matter.
  3. It observes the change in other properties of matter.

Understanding the concepts and formulas is cardinal to have a clearer idea about kinetic theory. Today, it is considered one of the paramount concepts in modern science. For deeper cognizance, you can refer to videos on MSVgo. MSVgo is an app whose core doctrine is to persuade you to understand the conviction with examples or explanatory visualizations or animations.

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
  • Hydrogen
  • Ideal solutions
  • Introduction to Organic Chemistry
  • Ionic equilibria
  • Matter
  • Matter Around Us
  • Matter In Our Surroundings
  • Metallurgy
  • Metals And Non-Metals
  • Mole Concept and Stoichiometry
  • Natural Resources
  • Organic Chemistry – Basic Principles
  • Periodic Classification of Elements
  • Physical and Chemical Changes
  • Physical and Chemical Properties of Water
  • Polymers
  • Preparation, Properties and Uses of Compounds
  • 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
  • Human Population
  • Human Reproduction
  • Hygiene
  • Improvement In Food Resources
  • Integumentary System- Skin
  • Kingdom Fungi
  • Kingdom Monera
  • Kingdom Protista
  • 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
  • Reproductive Health
  • 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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