Topics
Chemical Reactions and Equations
- Chemical Equation
- Balancing Chemical Equation
- Types of Chemical Change or Chemical Reaction
- Direct Combination (or Synthesis) Reaction
- Decomposition Reactions
- Single Displacement Reactions
- Double Displacement Reaction
- Oxidation, Reduction and Redox Reactions
- Corrosion of Metals and Its Prevention
- Rancidity of Food and Its Prevention
Chemical Substances - Nature and Behaviour (Chemistry)
Acids, Bases and Salts
- Acids
- Bases (Alkalis)
- Indicators
- Properties of Acids
- Properties of Bases (Alkalis)
- Acid or a Base in a Water Solution
- Similarities and Differences Between Acids and Bases
- Strength of Acidic or Basic Solutions
- Salts
- Important Salts in Daily Life
- Preparation and Uses of Sodium Hydroxide
- Preparation and Uses of Bleaching Powder
- Preparation and Uses of Baking Soda
- Preparation and Uses of Washing Soda
- Preparation and Uses of Plaster of Paris
World of Living (Biology)
Metals and Non Metals
- Types of Elements: Metals
- Physical Properties of Metals
- Chemical Properties of Metal
- Types of Elements: Non-metal
- Physical Properties of Non-metal
- Chemical Properties of Non-metal
- Electrovalent (or Ionic) Bond
- Reactivity Series of Metals
- Extraction of Metals
- Refining of Metals
- Corrosion of Metals and Its Prevention
- The Covalent Bond
Natural Phenomena (Physics)
Carbon and its Compounds
- Carbon: a Versatile Element
- The Covalent Bond
- Saturated and Unsaturated Carbon Compounds
- Allotropy and Allotropes of Carbon
- Crystalline Allotropes of Carbon: Diamond
- Crystalline Allotropes of Carbon: Graphite
- Crystalline Allotropes of Carbon: Fullerene
- Chains, Branches and Rings of Carbon Compound
- Functional Groups in Carbon Compounds
- Homologous Series of Carbon Compound
- Nomenclature of Organic Compounds (IUPAC)
- Chemical Properties of Carbon Compound
- Ethanol
- Ethanoic Acid
- Soap
- Detergents
- Cleansing Action of Soap
Effects of Current (Physics)
Natural Resources
Periodic Classification of Elements
- History of Periodic Table: Early Attempts at the Classification of Elements
- Dobereiner’s Triads
- Newland's Law of Octaves
- Mendeleev’s Periodic Table
- Merits and Demerits of Mendeleev’s Periodic Table
- The Modern Periodic Table
- Periodic Properties
- Periodic Properties: Valency
- Periodic Properties: Atomic Radius Or Atomic Size
- Periodic Properties: Metallic Character
- Periodic Properties: Non-metallic Character
Life Processes
- Living Organisms and Life Processes
- Nutrients and Nutrition
- Mode of Nutrition in Plant
- Autotrophic Nutrition
- Heterotrophic Nutrition
- Different Ways of Taking Food
- Human Digestive System
- The Mouth and Buccal Cavity
- The Teeth and Its Structure
- The Salivary Glands
- Swallowing and Peristalsis
- The Food Pipe/Oesophagus
- The Stomach
- The Small Intestine
- Pancreas
- Absorption of Food
- The Large Intestine
- Assimilation of Food
- Liver
- Respiration
- Respiration in Organisms
- Breathing in Other Animals
- Osmoregulation
- Types of Respiration: Aerobic and Anaerobic Respiration
- Human Respiratory System
- Circulation
- Blood
- Composition of Blood: Plasma (The Liquid Portion of Blood)
- Composition of Blood: Red Blood Cells (Erythrocytes)
- Composition of Blood: White Blood Cells (Leukocytes)
- Composition of Blood: Blood Platelets (Thrombocytes)
- Blood Circulatory System in Human
- Human Heart
- Blood Vessels – Arteries, Veins, and Capillaries
- Circulation of Blood in the Heart (Functioning of Heart)
- Types of Blood Circulation
- Heart Beat - Heart Sounds "LUBB" and "DUP"
- Function of Platelets - Clotting of Blood (Coagulation)
- Lymph and Lymphatic System
- Blood Pressure (B.P.)
- Transportation of Water and Food in Plants
- Water and Mineral Absorption by Root
- Translocation of Water (Ascent of Sap)
- Translocation of Mineral Ions
- Transport of Food
- Transpiration
- Excretion: Substances to Be Eliminated
- Human Excretory System
- Function of the Kidney - “Production of Urine”
- Excretion in Plants
Internal assessment
Control and Co-ordination
- Control and Co-ordination in Animals
- Human Nervous System
- Neuron (Or Nerve Cell) and Its Types
- Neuron as Structural and Functional Unit of Neural System
- Nerve Fibres
- Major Division of the Nervous System
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
- The Human Brain
- Central Nervous System (CNS): Structure of Human Brain
- Reflex and Reflex Action
- Nervous Pathways in Reflexes
- Reflex Arc
- Co-ordination in Plant: Tropism in Plants
- Hormones
- Plant Hormones
- Types of Plant Hormones: Auxins
- Types of Plant Hormones: Gibberellins
- Types of Plant Hormones: Ethylene
- Types of Plant Hormones: Cytokinins
- Types of Plant Hormones: Abscisic Acid (ABA)
- Types of Plant Hormones: Ethylene
- Hormones in Animals
- Human Endocrine System
- Pituitary Gland or Hypophysis Gland
- Thyroid Gland
- Parathyroid Gland
- Pancreas (Islets of Langerhans)
- Adrenal Gland (Suprarenal Gland)
- Reproductive Glands (Gonads)
- Thymus Gland
How do Organisms Reproduce?
- Accumulation of Variation During Reproduction
- Reproduction in Plant
- Mode of Reproduction in Plant
- Asexual Reproduction in Plant
- Natural Vegetative Reproduction
- Sexual Reproduction in Flowering Plants
- Sexual Reproduction in Animals
- Human Reproductive System
- The Male Reproductive System
- The Female Reproductive System
- Menstrual Cycle (Ovarian Cycle)
- Reproductive Health
- Sexually Transmitted Diseases (STD)
Heredity and Evolution
- Accumulation of Variation During Reproduction
- Heredity
- Gregor Johann Mendel – Father of Genetics
- Inheritance of One Gene (Monohybrid Cross)
- Inheritance of Two Genes (Dihybrid Cross)
- Mendelian Inheritance - Mendel’s Laws of Heredity
- Sex Determination
- Evolution
- Lamarck’s Theory of Evolution
- Darwin’s Theory of Natural Selection
- Theories of Origin of Life
- Speciation
- Evolution and Classiffication
- Evidences for Biological Evolution
- Paleobotany
- Evolution by Stages
- Origin and Evolution of Man
Light - Reflection and Refraction
- Reflection of Light
- Law of Reflection of Light
- Mirrors and Its Types
- Plane Mirror and Reflection
- Spherical Mirrors
- Rules for the Construction of Image Formed by a Spherical Mirror
- Images Formed by Spherical Mirrors
- Concave Mirror
- Image Formation by Concave Mirror
- Convex Mirror
- Image Formation by Convex Mirror
- Sign Convention for Reflection by Spherical Mirrors
- Mirror Equation/Formula
- Linear Magnification (M) Due to Spherical Mirrors
- Refraction of Light
- Refraction of Light Through a Rectangular Glass Slab
- Law of Refraction of Light
- Refractive Index
- Spherical Lens
- Images Formed by Sperical Lenses
- Guideline for Image Formation Due to Refraction Through a Convex and Concave Lens
- Concave Lens
- Images Formed Due to Refraction Through a Concave Lens
- Convex Lens
- Images Formed Due to Refraction Through a Convex Lens
- Sign Convention for Spherical Lenses
- Lens Formula
- Magnification Due to Spherical Lenses
- Power of a Lens
The Human Eye and the Colourful World
- Human Eye: Structure of the Eye
- Working of the Human Eye
- Eye Defect and Its Correction: Myopia Or Near-sightedness
- Eye Defect and its correction: Hypermetropia or far-sightedness
- Eye Defect and Its Correction: Presbyopia
- Care of the Eyes
- Refraction of Light Through a Prism
- Prism
- Dispersion of Light Through Prism and Formation of Spectrum
- Atmospheric Refraction
- Application of Atmospheric Refraction
- Scattering of Light and Its Types
- Applications of Scattering of Light
Electricity
- Electricity
- Electric Current
- Electric Circuit
- Potential and Potential Difference
- Symbols and Functions of Various Components of an Electric Circuits
- Ohm's Law (V = IR)
- Factors Affecting the Resistance of a Conductor
- Electrical Resistivity and Electrical Conductivity
- Resistors in Series
- Resistances in Parallel
- Effects of Electric Current
- Heating Effect of Electric Current
- Electrical Power
Magnetic Effects of Electric Current
- Magnetic Effect of Electric Current
- Magnetic Field
- Magnetic Field Lines
- Magnetic Field Due to a Current Carrying Straight Conductor
- Rule to Find the Direction of Magnetic Field
- Magnetic Field Due to Current in a Loop (Or Circular Coil)
- Magnetic Field Due to a Current Carving Cylindrical Coil (or Solenoid)
- Force on a Current Carrying Conductor in a Magnetic Field
- Electric Motor
- Electromagnetic Induction
- Faraday's Laws of Electromagnetic Induction
- Electric Generator
- Alternating Current (A.C.) Generator
- Direct Current Motor
- Household Electrical Circuits
- Distinction Between an A.C. Generator and D.C. Motor
- Types of current: Alternating Current (A.C.) and Direct Current (D.C.)
Sources of Energy
- Source of Energy
- Conventional Sources of Energy and Non-conventional Sources of Energy
- Fossil Fuels
- Heat Energy (Thermal Energy)
- Hydroelectric Energy
- Bio-energy
- Wind Energy
- Solar Energy
- Solar Energy Devices
- Energy from the Sea
- Geothermal Energy
- Nuclear Energy
- Nuclear Fission
- Different Forms of Energy
- Environmental Consequences
- How Long Will an Energy Source Last Us?
Our Environment
- The Environment
- Ecosystem
- Structure of an Ecosystem
- Classification of Animal
- Food Chain
- Tropic Level
- Food Web
- Energy Flow in an Ecosystem
- Ozone Layer Depletion
- Waste and Its Categories
- Wastes Generated in Our Environment
- Waste Separation Exercise
- Solid Waste Management
Sustainable Management of Natural Resources
- Sustainability of Natural Resources
- Case Study: Ganga Pollution and Ganga Action Plan
- Solid Waste Management
- Five R’s of Waste Management
- Conservation and Judicious Use of Resources
- Forests: Our Lifeline
- Stakeholders of Forest
- Conservation of Forest
- Conservation of Wildlife
- Water Management (Conservation of Water)
- Fresh Water Management
- Non-crystalline/Amorphous Forms: Coal
- Petroleum
- Conservation of Coal, Petroleum, and Natural Resources
- Overview of Natural Resource Management
- Chemical Equation
- Need for Chemical equation
- Limitation of Chemical equation
Chemical Equation
A chemical equation is a shorthand way to represent the components of a chemical reaction. Several pieces of information are provided in a chemical equation for those working with the chemical equation or corresponding chemical reaction.
You've worked with equations in mathematics, where an equation represents information such as equalities or inequalities. Chemical equations are different from mathematical equations because the two parts of a chemical reaction represent the 'before' and 'after' of a chemical reaction. In mathematical equations, an equals sign separates the two parts of the equation. In chemical equations, equal signs are not used. Instead, an arrow is used to separate the two sides of the equation, and it points in the direction that a chemical reaction will proceed.
Writing a Chemical Equation: A chemical equation represents a chemical reaction. If you recall formulae of magnesium, oxygen and magnesium oxide, the above word equation can be written as
Mg + O2 → MgO
Count and compare the number of atoms of each element on the LHS and RHS of the arrow. Is the number of atoms of each element the same on both sides? If yes, then the equation is balanced. If not, then the equation is unbalanced because the mass is not the same on both sides of the equation.
Notes
When a chemical reaction occurs, the mass of the products should equal the mass of the reactants. A balanced chemical equation occurs when the number of atoms involved on the reactants side equals the number of atoms on the product side.
Zinc + Sulphuric acid → Zinc sulphate + Hydrogen
The following chemical equation may represent the above word equation –
Zn + H2SO4 → ZnSO4 + H2
Let us examine the number of atoms of different elements on both sides of the arrow.
Element |
Number of atoms in reactants (LHS) |
Number of atoms in products (RHS) |
Zn | 1 | 1 |
H | 2 | 2 |
S | 1 | 1 |
O | 4 | 4 |
As the number of atoms of each element is the same on both sides of the arrow, it is a balanced chemical equation.
Let us try to balance the following chemical equation –
Fe + H2O → Fe3O4 + H2
Step I: To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation.
Fe + H2O → Fe3O4 + H2
Step II: List the number of atoms of different elements present in the unbalanced equation.
Elements | Number of atoms in reactants (LHS) | Number of atoms in products (RHS) |
Fe | 1 | 3 |
H | 2 | 2 |
O | 1 | 4 |
Step III: It is often convenient to start balancing with the compound that contains the maximum number of atoms. It may be a reactant or a product. In that compound, select the element with the maximum number of atoms. Using these criteria, we select Fe3O4 and the element oxygen in it. There are four oxygen atoms on the RHS and only one on the LHS. To balance the oxygen atoms.
Atoms of oxygen | In reactants | In products |
(i) Initial | 1 (in H2O) | 4 (in Fe3O4) |
(ii) To balance | 1`xx`4 | 4 |
To equalise the number of atoms, it must be remembered that we cannot alter the formulae of the compounds or elements involved in the reactions. For example, to balance oxygen atoms, we can put coefficient 4’ as 4 H2O, not H2O4 or (H2O)4. Now the partly balanced equation becomes–
Fe + 4H2O → Fe3O4 + H2
Step IV: Fe and H atoms are still not balanced. Pick any of these elements to proceed further. Let us balance hydrogen atoms in the partly balanced equation. To equalise the number of H atoms, make the number of molecules of hydrogen four on the RHS.
Atoms of hydrogen | In reactants | In products |
(i) Initial | 8 (in 4 H2O) | 2 (in H2) |
(ii) To balance | 8 | 2`xx`4 |
Fe + 4H2O → Fe3O4 + 4H2
Step V: Examine the above equation and pick up the third element which is not balanced. You find that only one element is left to be balanced, that is, iron.
Atoms of iron | In reactants | In products |
(i) Initial | 1 (in Fe) | 3 (in Fe3O4) |
(ii) To balance | 1`xx`3 | 3 |
To equalise Fe, we take three atoms of Fe on the LHS.
3Fe + 4H2O → Fe3O4 + 4H2
Step VI: Finally, to check the correctness of the balanced equation, we count atoms of each element on both sides of the equation.
3Fe + 4H2O → Fe3O4 + 4H2
The numbers of atoms of elements on both sides of the eq are equal. This equation is now balanced. This method of balancing chemical equations is called the hit-and-trial method, as we make trials to balance the equation by using the smallest whole-number coefficient.
To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s), respectively. Aqueous (aq) is written if the reactant or product is present as a solution in water. The balanced Eq becomes
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)