Topics
Chemical Substances - Nature and Behaviour
Carbon Compounds
- Concept of Carbon
- Bonding in Carbon - Covalent Bond
- Versatile Nature of Carbon
- Saturated and Unsaturated Carbon Compounds
- Chains, Branches and Rings of Carbon Compound
- Homologous Series of Carbon Compound
- Nomenclature of Carbon Compounds
- Chemical Properties of Carbon Compounds - Combustion
- Chemical Properties of Carbon Compounds - Addition Reaction
- Chemical Properties of Carbon Compounds - Substitution Reaction
- Properties of Ethanol
- Properties of Ethanoic Acid
- Soaps and Detergents
Metals and Non Metals
- Metal and Its Physical Properties
- Non Metals and Its Physical Properties
- Chemical Properties of Metals: When Metals Are Burnt in Air
- Chemical Properties of Metals: When Metals React with Water
- Chemical Properties of Metals: When Metals React with Acids
- Chemical Properties of Metals: Metals React with Solutions of Other Metal Salts
- Chemical Properties of Metals: Reactivity Series
- Reaction of Metals with Non-metals
- Formation and Properties of Ionic Compounds
- Occurrence of Metals
- Extraction of Metals from Ore
- Enrichment of Ores
- Extracting Metals Low in the Activity Series
- Extracting Metals in the Middle of the Activity Series
- Extracting Metals Towards the Top of the Activity Series
- Refining of Metals
- Concept of Corrosion of Metals and Its Prevention
Periodic Classification of Elements
Acids, Bases and Salts
- Concept of Acid and Its Properties
- Concept of Base
- Acid and Base Indicator
- Chemical Properties of Acids and Bases
- Reaction of Acids and Bases with Metals
- Reaction of Acids with Metal Carbonates and Hydrogencarbonates
- Reaction of Metallic Oxides with Acids
- Reaction of a Non-metallic Oxide with Base
- Acids and Bases React with Each Other
- Acid Or a Base in a Water Solution
- Strength of Acids and Bases
- Concept of Salts
- Ph of Salts
- Chemicals from Common Salt
- 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
Chemical Reactions
- Concept of Physical Changes
- Concept of Chemical Changes
- Concept of Chemical Reactions
- Chemical Equation
- Balancing of a Chemical Equation
- Combination Reaction
- Decomposition Reactions
- Displacement Reaction
- Double Displacement Reaction
- Oxidation and Reduction
- Concept of Corrosion of Metals and Its Prevention
- Concept of Rancidity
- Endothermic and Exothermic Reactions
World of Living
Heredity and Evolution
- Evolution and Classification - Introduction
- Accumulation of Variation During Reproduction
- Heredity - Inherited Traits
- Rules for the Inheritance of Traits - Mendel’S Contributions
- Sex Determination in Humans
- Concepts of Evolution
- Evolution - Acquired and Inherited Traits
- Speciation
- Heredity and Evolution
- Evolution and Classification - Tracing Evolutionary Relationships
- Evolution and Classification - Fossils
- Evolution by Stages
- Human Evolution
Reproduction
- Reproduction in Plant
- Reproductive Health - Need and Methods of Family Planning
- Modes of Reproduction Used by Single Organisms - Fission
- Modes of Reproduction Used by Multicellular Organisms - Fragmentation
- Modes of Reproduction Used by Multicellular Organisms - Regeneration
- Modes of Reproduction Used by Single Organisms - Budding
- Modes of Reproduction Used by Multicellular Organisms - Vegetative Propagation
- Modes of Reproduction Used by Multicellular Organisms - Spore Formation
- Sexual Reproduction in Animals
- Sexual Reproduction in Flowering Plants
- Human Reproductive System
- Reproduction in Plant
Control and Co-ordination in Animals and Plants
- Control and Co-ordination Introduction
- Tropic Movements in Plants
- Coordination in Plants - Movement Due to Growth
- Coordination in Plants - Immediate Response to Stimulus
- Hormones in Animals
- Control and Co-ordination in Animals
- Importance of Variation
- Animals – Nervous System
- Human Brain - Voluntary Action
- Human Brain - Involuntary Action
- Human Brain - Reflex Action
- Control and Co-ordination Questions
Life Processes
Natural Phenomena
- Refraction of Light
- Spherical Mirrors
- Concave Mirror
- Convex Mirror
- Concave Mirror
- Convex Mirror
- Sign Convention for Reflection by Spherical Mirrors
- Linear Magnification (M) Due to Spherical Mirrors
- Velocity of Light
- Refraction of Light
- Refraction Through a Rectangular Glass Slab
- Refractive Index
- Refraction by Spherical Lenses
- Convex Lens
- Concave Lens
- Convex Lens
- Concave Lens
- Sign Convention for Spherical Lenses
- Magnification of a Lens
- Power of a Lens
- Concept of Human Eye
- Defects of Vision and Their Correction
- Applications of Spherical Mirrors and Lenses
- Dispersion by a Prism
- Atmospheric Refraction
- Some Natural Phenomena Due to Sunlight
Effects of Current
Magnetic Effects of Current
- Magnetic Effect of a Current
- Magnetic Field Lines
- Magnetic Force
- The Bar Magnet
- Magnetic Field Due to a Current carrying Straight Conductor
- Right-Hand Thumb Rule
- Magnetic Field Due to a Current Through a Circular Loop
- Magnetic Field Due to a Current in a Solenoid
- Force Acting on Current Carrying Conductor in a Magnetic Field
- Fleming’s Left Hand Rule
- Electric Motor
- Electromagnetic Induction
- Electric Generator - Ac
- Domestic Electric Circuits
- Alternating Current (AC) and Direct Current (DC)
- Introduction of Magnetism
Effects of Current
- Effects of Current Introduction
- Electric Current
- Electric Potential
- Electric Potential Difference
- Electric Circuit
- Ohm’s Law
- Factors on Which the Resistance of a Conductor Depends
- Resistance of a System of Resistors - Resistors in Series
- Resistance of a System of Resistors - Resistors in Parallel
- Heating Effect of Electric Current
- Electric Power
- Effects of Current Numericals
Natural Resources
Management of Natural Resources
- Conservation and Judicious Use of Natural Resources
- Need to Manage Our Resources
- Forests and Wild Life - Stakeholders
- Forests and Wild Life - Sustainable Management
- Coal and Petroleum
- Water for All - Dams
- Water for All - Water Harvesting
- Overview of Natural Resource Management
- Sustainability of Natural Resources
- Concept of Rainwater Harvesting (Importance)
Our Environment
Sources of Energy
- Sources of Energy Introduction
- Good Source of Energy
- Different Forms of Energy
- Conventional Sources of Energy
- Conventional Sources of Energy - Thermal Power Plant
- Conventional Sources of Energy - Hydro Power Plants
- Improvements in the Technology for Using Conventional Sources of Energy
- Alternative or Non-conventional Sources of Energy - Solar Energy
- Alternative or Non-conventional Sources of Energy - Energy from the Sea
- Alternative Or Non-conventional Sources of Energy - Geothermal Energy
- Alternative or Non-conventional Sources of Energy - Nuclear Energy
- Environmental Consequences
- Energy Source - How Long Will Last Us
- Renewable Versus Non-renewable Sources
description
- Chemical Equation
- Word equation
- Symbols of elements and their valencies
- Writing a Chemical Equations
notes
A chemical equation is a short-hand way to represent the components of a chemical reaction. There are several pieces of information 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 is used to represent 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 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 the 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 be equal to the mass of the reactants.A balanced chemical equation occurs when the number of the atoms involved in the reactants side is equal to the number of atoms in the product side.
Zinc + Sulphuric acid → Zinc sulphate + Hydrogen
The above word-equation may be represented by the following chemical 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 which has 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 equalize 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 and 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 equalize the number of H atoms, make the number of molecules of hydrogen as 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 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. The word 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)
