Grade 7
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Scientific Method in Chemistry  1.5. Laboratory Safety Rules and Precautions  1.6. Common Laboratory Equipment and Their Uses  1.7. Units of measurement in chemistry
  2. Matter and its properties  2.1. Definition of Matter  2.2. Classification of matter  2.3. Properties of matter  2.3.1. Physical properties  2.3.2. Chemical properties  2.4. States of matter  2.4.1. Solid state  2.4.2. Fluid state  2.4.3. Gaseous state  2.4.4. Plasma and Bose–Einstein condensates  2.5. Changes in the states of matter  2.5.1. Melting and freezing  2.5.2. Evaporation and Condensation  2.5.3. Sublimation and deposition  2.6. Density and its applications  2.7. Diffusion and its importance
  3. Elements, Compounds, and Mixtures  3.1. Definition of the element  3.2. Classification of elements  3.3. Metals, Nonmetals and Metalloids  3.4. Noble gases and their properties  3.5. Introduction to the Periodic Table  3.6. Definition of Compound  3.7. Properties of Compounds  3.8. Introduction to Chemical Formulas  3.9. Definition of Mixture  3.10. Types of mixtures  3.10.1. Homogeneous mixture  3.10.2. Heterogeneous mixtures  3.11. Difference Between Compounds and Mixtures  3.12. Solutions, Colloids and Suspensions
  4. Separation of mixtures  4.1. Need for separation of mixtures  4.2. Separation methods  4.2.1. Filtration  4.2.2. Sedimentation and decantation  4.2.3. Evaporation  4.2.4. Crystallization  4.2.5. Distillation  4.2.6. Chromatography  4.2.7. Magnetic Separation  4.2.8. Centrifugation
  5. Atomic Structure  5.1. Introduction to Atoms  5.2. Structure of the atom  5.2.1. Nucleus and electron cloud  5.3. Subatomic particles  5.3.1. Proton  5.3.2. Neutron  5.3.3. Electrons  5.4. Atomic number and mass number  5.5. Isotopes and their uses  5.6. Ions and ion formation
  6. Periodic table  6.1. Introduction to the Periodic Table  6.2. Groups and periods  6.3. Trends in the Periodic Table  6.3.1. Atomic Size  6.3.2. Metallic and non-metallic character  6.3.3. Electronegativity  6.3.4. Reactivity of the elements  6.4. Alkali metals and their properties
  7. Chemical bond  7.1. Why do atoms form bonds?  7.2. Types of chemical bonds  7.2.1. Ionic bond  7.2.2. Covalent bond  7.2.3. Metal Bond  7.3. Properties of Ionic and Covalent Compounds  7.4. Intermolecular forces
  8. Chemical reactions  8.1. Introduction to Chemical Reactions  8.2. Signs of a chemical reaction  8.3. Types of Chemical Reactions  8.3.1. Combination Reactions  8.3.2. Decomposition reactions  8.3.3. Displacement reactions  8.3.4. Double displacement reactions  8.3.5. Combustion reactions  8.4. Law of conservation of mass  8.5. Balancing simple chemical equations
  9. Acids, Bases and Salts  9.1. Definition of Acid and Base  9.2. Properties of Acids  9.3. Properties of bases  9.4. pH Scale and Indicators  9.5. Neutralization reactions  9.6. Common Acids and Bases in Everyday Life  9.7. Preparation and use of salts  9.8. Strong and weak acids and bases
  10. Solutions and Solubility  10.1. Definition of Solution  10.2. Components of the solution  10.2.1. Solvent  10.2.2. solute  10.3. Factors Affecting Solubility  10.4. Concentration of solutions  10.5. Saturated and unsaturated solutions  10.6. Colloids and suspensions  10.7. Solubility curve and its interpretation
  11. Air and atmosphere  11.1. Composition of air  11.2. Properties of gases in the air  11.3. Importance of Oxygen and Carbon Dioxide  11.4. Air pollution and its effects  11.5. Greenhouse effect and global warming  11.6. Ways to reduce air pollution  11.7. Ozone layer and its importance
  12. Water and its importance  12.1. Properties of Water  12.2. Water as the universal solvent  12.3. Importance of water for life  12.4. Water pollution and its effects  12.5. Water Purification  12.5.1. Filtration  12.5.2. boil  12.5.3. Chlorination in water purification  12.5.4. reverse osmosis  12.6. Hard and soft water  12.7. Water cycle and its importance
  13. Fuel and energy  13.1. Types of fuel  13.1.1. Fossil fuels  13.1.2. Renewable energy sources  13.2. Combustion and energy release  13.3. Global warming and its effects  13.4. Alternative sources of energy  13.5. Ways to conserve energy
  14. Metals and Nonmetals  14.1. Physical and chemical properties of metals  14.2. Physical and Chemical Properties of Non-Metals  14.3. Difference Between Metals and Nonmetals  14.4. Uses of metals and nonmetals  14.5. Corrosion of metals and its prevention  14.6. Alloys and their importance
  15. Plastics and polymers  15.1. Natural and synthetic polymers  15.2. Properties of plastics  15.3. Biodegradable and Non-Biodegradable Plastics  15.4. Environmental impact of plastic  15.5. Recycling and waste management in plastics and polymers  15.6. Daily Uses of Polymers
  16. Introduction to Organic Chemistry  16.1. Basic definitions of organic chemistry  16.2. Carbon Compounds in Daily Life  16.3. Hydrocarbons  16.4. Simple functional groups (alcohols and carboxylic acids)  16.5. Importance of organic compounds in industry

Grade 7 → Chemical reactions ↓


Balancing simple chemical equations


Chemistry is a fascinating subject that helps us understand the world around us at the molecular level. One of the fundamental skills in chemistry is balancing chemical equations. In this guide, we'll explore what chemical equations are and how to balance them.

What is the chemical equation?

A chemical equation is a written representation of a chemical reaction. It shows the reactants, i.e. the substances that start the reaction, and the products, i.e. the substances produced by the reaction.

For example, consider the chemical equation for the reaction of hydrogen and oxygen to form water:

H 2 + O 2 → H 2 O

In this equation, H 2 and O 2 are the reactants, and H 2 O is the product.

Why balance chemical equations?

Chemical equations must be balanced to satisfy the law of conservation of mass. This law states that mass cannot be created or destroyed in a chemical reaction. Therefore, the number of atoms of each type must be the same on both sides of the equation.

Returning to our previous example:

H 2 + O 2 → H 2 O

The equation is still not balanced. There are 2 hydrogen atoms and 2 oxygen atoms on the reactant side, but there are only 2 hydrogen atoms and 1 oxygen atom on the product side.

Steps to balancing chemical equations

Let's look at the steps to balance a chemical equation.

  1. Identify each element in the equation.

    2. Examine each side of the equation. Identify and list all the elements involved in the reaction.

  2. Write the number of atoms of each element.

    3. Count the number of atoms of each element on both sides of the equation.

    Example:

    H 2 + O 2 → H 2 O

    Reactants: 2 H, 2 O
    Product side: 2 H, 1 O

  3. Use the coefficients to balance the equation.

    4. Adjust the coefficients (the numbers in front of the molecules) to balance the number of atoms on each side. The coefficients are whole numbers.

    For example, update the equation to balance the oxygen:

    2H 2 + O 2 → 2H 2 O

    Now, the number of atoms is balanced: Reactant side: 4 H, 2 O
    Product side: 4 H, 2 O

  4. Check your work.

    5. Make sure the equation is balanced by recounting the atoms. There should be the same number of atoms of each element on each side of the equation.

More examples of balancing simple chemical equations

Example 1: Formation of carbon dioxide

In this example, carbon and oxygen combine to form carbon dioxide:

C + O 2 → CO 2

Steps to balance:

  1. List the elements: C, O
  2. Count the atoms on each side: Reactant side: 1 C, 2 O
    Product side: 1C, 2O
  3. The equation is balanced as written.

Example 2: Formation of aluminium oxide

Consider the reaction of aluminum with oxygen to form aluminum oxide:

Al + O 2 → Al 2 O 3

Steps to balance:

  1. List the elements: Al, O
  2. Count the atoms on each side: Reactant side: 1 Al, 2 O
    Product side: 2 Al, 3 O
  3. Use coefficients to balance: - Balance the Al: 2Al + O 2 → Al 2 O 3
  4. Balance the O using the coefficient of 3 for O 2: 4Al + 3O 2 → 2Al 2 O 3
  5. Check: Reactant side: 4 Al, 6 O
    Product side: 4 Al, 6 O
  6. Now it is balanced.

Visualizing the process

Let's use a diagram to show the balance of the reaction between hydrogen and oxygen to form water:

H2 O2 H H O

These circles represent molecules. By adjusting the number of these circles, we show how the equation is balanced to reflect the number of atoms present on each side of the reaction.

Practice problems

Here are some practice problems you can try to test your skills:

Problem 1: Hydrogen and chlorine

H 2 + Cl 2 → HCl

Solution:

H 2 + Cl 2 → 2HCl

A balanced equation with 2 molecules of HCl was produced.

Problem 2: Methane combustion

CH 4 + O 2 → CO 2 + H 2 O

Solution:

CH 4 + 2O 2 → CO 2 + 2H 2 O

The combustion of methane produces equal numbers of water molecules and carbon dioxide molecules.

Problem 3: Iron and oxygen

Fe + O 2 → Fe 2 O 3

Solution:

4Fe + 3O 2 → 2Fe 2 O 3

Iron reacts with oxygen to form iron(III) oxide or rust.

Practice makes perfect, and these fundamental exercises are vital to understanding more complex chemical reactions.


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