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Chapter 6 – Changes Around Us

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

Introduction

Every second, everything around us is continually changing. From our hair and nails growing to our lungs expanding and contracting while breathing to the movement of the moon. Our environment is constantly changing. Some of these changes are temporary, meaning they can change back to their original form, while some are permanent, meaning they can’t go back to their original state. A few of these changes are not even noticeable. Let’s understand what these changes really mean.

Any difference in the shape or size of an object is referred to as a change. Some changes can always be reversed, while some can’t. Based on this, you can classify changes into two broad categories (1) Reversible and (2) Irreversible changes- 

(1) Reversible changes are the type of changes that can be undone or reversed. 

  • When you can go back to the substance you started with, it is called reversible change. 
  • In a majority of cases, a new substance is not formed in a reversible change. For example, you stretch a rubber band, your lungs expand when you breathe, you fold a sheet of paper.
  • Sometimes, the physical properties of the material change. For example, water becomes steam when heated.

(2) Irreversible changes are the type of changes that cannot be undone or reversed.

  • It’s a type of change you cannot reverse using any chemical or physical means, no matter what you do.  
  • A new substance is almost always formed during this change.
  • A good example is the burning of coal, a chemical change. It’s irreversible because a new substance is formed, which cannot be changed back to coal.

Apart from reversible and irreversible changes, there is another way to classify changes – Physical and Chemical changes.

(1) Physical changes affect the physical properties of a substance, but the chemical properties remain the same. For example, boiling water, freezing water, melting wax, etc. 

  • Usually, physical changes do not involve the production of energy.
  • No new substances are formed during such physical changes.
  • Unlike chemical changes, the original substance can be recovered after the physical change. For example, water can be converted back into liquid form from steam. 
  • Physical change is temporary and not permanent. 

(2) Chemical changes affect both the chemical and physical properties of a substance. For example, digestion of food, burning of coal or paper. 

  • One or more new substances always accompany a chemical change. For example, the burning of coal leads to the creation of ashes and gasses like CO2, SO2, NOx.
  • Chemical changes are permanent.
  • Chemical changes often lead to the production of energy like sound, light, heat, etc.
  • Most of the time, chemical changes are irreversible, i.e., the original substance cannot be recovered.

Expansion and contraction

  • If you increase the temperature, the particles of a substance expand or loosen. A common example of expansion is the railway tracks during summers, as steel expands when heated. 
  • If you decrease the temperature, the particles of a substance contract or become tighter. A common example of this contraction is railway tracks during winters, as steel contracts under low temperatures. 
  • This expansion and contraction are different for different states of matter like solid, liquid, and gasses. A good example that covers all this is water as it can transform into liquid (water), solid (ice), and gasses (steam).
  • At less than 0°C or 0°C, water will turn into ice. This process is known as freezing. You apply heat to it, and it will turn into its liquid form. This process is called melting and will remain in its liquid form till the temperature reaches 99°C. When the temperature reaches 100°C, water will start to boil and turn into steam. This process is called evaporation.  
  • Water can also be converted into its liquid form from steam by a process known as condensation. Condensation is the process of the physical state of matter changing from the gaseous to the liquid phase. This is achieved by lowering the temperature surrounding the matter. 
  • Water also expands and contracts like steel, and on reducing the temperature, water contracts. Like most other liquids, it will contract until it reaches approximately 4°C. After that, it does something different from most liquids. It expands slightly till it reaches the freezing point. Other liquids continue to contract at this point. When water freezes, it expands by approximately 9%, which is different from how most liquids behave.

Burning or combustion is an irreversible process where a substance burns to produce a new substance. A good example of this is coal burning; burning coal produces fly ash and various other gasses like CO2, NOx, SO2, and particulate matter that causes pollution.

Many substances you see around you are not in their pure form. They are a mixture of two or maybe more than two substances. You can separate different substances of a mixture to obtain individual components that make up the mixture. A good example is water sedimentation, where you separate impurities like dirt and mud from water to obtain pure water.

It is fascinating to know that every object around you is undergoing some change at all times. Many changes are based purely on heat, and the level and speed of change depend on the heat supplied. Supply enough heat, and you can change the state of any object around you. From simple substances like water to complex ones like coal, when changed, produces results different from a substance like water. 

  • What are the changes around us? 

Rotation of earth, rise, and fall of temperature, melting of ice to become water are examples of changes around us. 

  • What are the physical changes for Class 6? 

Boiling water, folding paper, and cutting wood. 

  • Why do changes occur around us? Explain with examples. 

Changes occur around us all the time; sometimes, these changes happen instantaneously and sometimes slowly. Changes can be classified into 4 types- 

Physical changes: They only change the physical attributes of the material and not the chemical composition. For example, the melting of ice. 

Chemical changes: They change the physical and chemical composition of the material. For example, burning coal. 

Reversible changes: These changes can be reversed. For example, water can be frozen once again when obtained from melting ice. 

Irreversible changes: They cannot be reversed. For example, if you burn paper, you cannot make paper from ashes. 

  • What changes take place naturally? 

Rotting of food, rotation of the earth, and movement of the moon.

  • What are the two types of changes? 

The two types of changes are reversible and irreversible changes. Reversible changes can be undone or reversed, e.g., melting of ice. Irreversible changes can’t be undone or reversed, e.g., burning of coal. 

  • What are physical and chemical changes for class 6?

Physical changes are- melting of ice, cutting paper, folding clothes. 

Chemical changes are- digestion of food, ripening of a mango, burning coal.

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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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