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Chapter 2 – Chemical Changes and Reactions

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

Introduction

learnedshedsMany changes occur in nature, such as water evaporation, condensation, runoff, etc. The change of state is part of all these transitions. During any reaction, old bonds break in the reactants, and new bonds are formed in the materials.

The change in which the molecular structure is entirely changed and the new substance is produced is called a chemical change. During a chemical change, the mass of the substance is changed. Energy variations occur after a chemical change. There is a difference in energy between breaking old bonds in reactants and creating new bonds in materials. The reaction is termed an exothermic reaction when energy is emitted and an endothermic reaction when energy is consumed

The cause for different forms of reactions is the products generated, the changes that arise, the reactions involved, etc. There are different kinds of reactions:

  • Combustion reaction: A combustion reaction is a reaction with an oxidizing fuel to give an oxidized substance. The oxidizer is a chemical that has to be burned by gasoline, usually oxygen.
  • Decomposition reaction: A decomposition reaction is a reaction in which a single component is broken down into several components. Certain changes in the atmosphere’s energies have to be made, such as heat, light or electricity that breaks the bonds of the compound.
  • Neutralization reaction: The neutralization reaction is essentially the acid and the base’s reaction, giving salt and water as products. The water molecule is a mixture of OH– ions and H+ ions. The products’ total pH when a strong acid and a strong base undergo a neutralization reaction would be 7.
  • Redox reaction: A reduction-oxidation reaction is a reaction in which electrons are transferred between chemical compounds.
  • Precipitation or Double-Displacement reaction: It is a form of displacement reaction in which two compounds react and, as a result, their anions and cations turn into two new products.
  • Synthesis reaction: A synthesis reaction is one of the most common reactions in which several simple compounds interact to produce a complex product under certain physical conditions. The result is still going to be a compound.

Because energy is absorbed when chemical bonds are destroyed and released during their formation, chemical reactions nearly often require a change of energy between products and reactants. However, according to the Law of Energy Conservation, we know that the system’s overall energy must remain constant and that often the chemical reaction absorbs or releases energy in the form of heat, light, or both. The energy change in the chemical reaction is due to the differences in the amount of chemical energy deposited between ingredients and reactants. This accumulated chemical energy or heat content of the system is known as enthalpy.

It is a chemical reaction that starts with light absorbed as a source of energy. There are temporary peak states that get activated as the molecules absorb light, and there are significant changes in physical and chemical properties from the actual molecules.

Ideally, the photo-reaction mechanism should provide a thorough characterization of the key events as outlined in the photochemical reaction pathway classification. Quantum yield and rate constants are all related to photophysical and photochemical processes, along with details on the structure and fate of any reactive intermediates, their lifetimes and their reactivity.

An electrochemical reaction is a mechanism in which electrons, such as an electrolyte, move between a solid electrode and a substance. This flow induces an electrical current through the electrodes, which causes the reaction to release or absorb heat. Chemical reactions either consume or emit energy that may be in the form of electricity. Electrochemistry is a chemical division that talks about the transfer of chemical energy to electrical energy. It has many different uses in daily life. All kinds of batteries, from those used to power a torch to a calculator, depend on chemical reactions to produce energy. Electricity is used for plating objects with metals such as gold or chromium.

In this chapter, we learnt about the concepts of chemical changes and reactions. The chapter also shed some light on the nature and characteristics of chemical change.

  1. Give an example of a photochemical reaction.
    Photosynthesis is when plants convert carbon dioxide and water to glucose and oxygen using solar energy. E.g., the generation of human vitamin D by exposure to sunlight, the enzyme in the abdomen catalyzing a light-producing reaction in fireflies called bioluminescence.
  2. What is the primary photochemical process?
    Photolysis is the mechanism by which a photochemical reaction occurs. The subsequent effect of the absorption of light is the primary photochemical reaction. Secondary reactions are subsequent chemical changes.
  3. What is a chemical reaction?
    A chemical reaction breaks down the chemical bonds of the reactants (reacting compounds) to form new bonds and substances (products).
  4. Is the energy involved in a chemical change?
    Yes, regardless of the formation and breakdown of bonds, energy is involved in a chemical change. Energy is produced in exothermic reactions and absorbed in endothermic reactions.
  5. What are the fundamentals of chemical reactions?
    • They are a phase in which one or more compounds (reactants) are converted into separate substances known as products.
    • They rearrange the constituent atoms of the reactants to produce distinct molecules as products.
    • They are different from physical effects, including state changes, such as ice freezing to water and water evaporating to vapour. If a physical change happens, the material’s physical characteristics will change, but the chemical identity will stay the same.

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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
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  • Kinetic Theory
  • Law of motion
  • Light – Reflection And Refraction
  • Magnetic Effects Of Electric Current
  • Magnetism and Matter
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  • Mechanical properties of Fluids
  • Mechanical properties of Solids
  • Motion
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  • Paths of Heat
  • Physical world
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  • Semiconductor Devices
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  • Sources Of Energy
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  • Static Electricity
  • Systems of Particles and Rotational motion
  • Thermal properties of matter
  • Thermodynamics
  • Units and Measurement
  • Vectors, Scalar Quantities and Elementary Calculus
  • Wave Optics
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  • 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
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  • Mole Concept and Stoichiometry
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  • 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
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  • Cell – Unit of Life
  • Cell Cycle and Cell Division
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  • Chemical Coordination and Integration
  • Circulation
  • Control And Coordination
  • Crop Improvement
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  • Diversity In Living Organisms
  • Ecosystem
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  • Excretory Products and their Elimination
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High School Math

  • Algebra – Arithmatic Progressions
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  • 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
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  • Geometry – Area
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  • 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
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  • Forests: Our Lifeline
  • Friction
  • Fun With Magnets
  • Garbage In, Garbage Out
  • Getting To Know Plants
  • Health and Hygiene
  • Heat
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  • Life Processes: Nutrition in Animals and Plants
  • Light, Shadows And Reflections
  • Materials: Metals And Non-Metals
  • Matter and Its States
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  • 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
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  • Reaching The Age Of Adolescence
  • Reproduction In Animals
  • Reproduction In Plants
  • Respiration In Organisms
  • Rocks and Minerals
  • Separation Of Substances
  • Simple Machines
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  • 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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