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 ↓


Introduction to Chemical Reactions


Chemical reactions are an essential part of our world. They are happening all around us, all the time. Chemical reactions occur when substances, known as reactants, change into new substances, known as products. Understanding chemical reactions helps us understand the natural world, cook food, make products, and even breathe.

What is a chemical reaction?

In a chemical reaction, the molecules of one or more substances are rearranged to form different molecules. During this process, chemical bonds are broken, and new ones are formed. For example, when you burn wood in a fireplace, you are essentially causing a chemical reaction that turns wood and oxygen into ash, carbon dioxide, and water.

Basic concepts

Reactants and products

Let's consider a simple chemical reaction that occurs when hydrogen gas reacts with oxygen gas to form water. In this reaction, hydrogen and oxygen are the reactants, and water is the product. We can write this chemical reaction in a simplified form as follows:

2H 2 + O 2 → 2H 2 O

In this reaction, two molecules of hydrogen gas react with one molecule of oxygen gas to form two molecules of water. This is a balanced chemical equation where the number of atoms of each element is the same on both sides of the equation.

Signs of chemical reactions

How can you tell if a chemical reaction is taking place? There are several signs, including:

  • Colour change: A chemical reaction can cause a substance to change colour. For example, when iron rusts, it turns from a shiny metal to a brownish-red colour.
  • Temperature change: Reactions release or absorb heat. Combustion, like a campfire, releases heat.
  • Gas production: If you see bubbles forming in a liquid, it's often a sign that gas is forming. This is due to the release of carbon dioxide gas when you mix vinegar and baking soda.
  • Precipitate formation: During a chemical reaction, a solid may form in a liquid. This is often called a precipitate.
  • Light emission: Some reactions release energy in the form of light. A good example of this is fireworks.

Types of chemical reactions

Chemical reactions can be classified into different types. Understanding these types helps in classifying reactions and predicting products. Here are some basic types of chemical reactions:

Synthesis reactions

In a synthesis reaction, two or more simple substances combine to form more complex products. The general format is:

A + B → AB

For example, when sodium (Na) reacts with chlorine ( Cl2 ), they form sodium chloride (NaCl), which is common table salt.

2Na + Cl 2 → 2NaCl

Decomposition reactions

In decomposition reactions, a single compound breaks down into two or more simpler substances. The general format is:

AB → A + B

A practical example of this is when electricity is passed through water, it decomposes into hydrogen and oxygen gases.

2H 2 O → 2H 2 + O 2

Single replacement reactions

In a single replacement reaction, one element in a compound replaces another element. It follows this pattern:

A + BC → AC + B

An example of this is when zinc is mixed with hydrochloric acid, zinc chloride and hydrogen gas are produced.

Zn + 2HCl → ZnCl 2 + H 2

Double replacement reactions

Double replacement reaction involves the exchange of ions between two compounds and can be represented as follows:

AB + CD → AD + CB

A classic example of this is the reaction between silver nitrate (AgNO 3 ) and sodium chloride (NaCl) to form silver chloride (AgCl) and sodium nitrate (NaNO 3 ).

AgNO 3 + NaCl → AgCl + NaNO 3

Conservation of mass

A fundamental concept in chemistry is the conservation of mass. This law states that mass is neither created nor destroyed in a chemical reaction. This means that the mass of the reactants must equal the mass of the products. For example, when you mix vinegar and baking soda, the mass of the resulting products (including the gas given off) is equal to the mass of the vinegar and baking soda you started with.

Visualization of chemical reactions

Visualizing chemical reactions can be of great help in understanding chemistry. Let's use simple shapes to represent different atoms and depict a chemical reaction:

H2 O2 H2O H2O

In this simple visual example, we can see two hydrogen molecules reacting with one oxygen molecule to form two water molecules.

Balancing chemical equations

Chemical equations must be balanced to show conservation of mass. There must be the same number of atoms of each element on each side of the equation. Here is an example of balancing a chemical equation.

Consider the unbalanced equation for the combustion of ethene (C 2 H 4 ):

C 2 H 4 + O 2 → CO 2 + H 2 O

To balance this equation, make sure there are an equal number of atoms of each type on both sides. The balanced equation is:

C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O

This balanced equation shows us that one molecule of ethene reacts with three molecules of oxygen to form two molecules of carbon dioxide and two molecules of water.

Everyday chemical reactions

Chemical reactions aren't just for the laboratory; they exist in our daily lives too. Here are some common examples:

  • Photosynthesis: Plants use a chemical reaction called photosynthesis to convert carbon dioxide and water into glucose and oxygen. The overall equation is as follows: 
    6CO 2 + 6H 2 O + light energy → C 6 H 12 O 6 + 6O 2
  • Cellular respiration: This is how the cells in our body use oxygen to break down food molecules, producing energy, carbon dioxide, and water. The overall equation is: 
    C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + energy

Learning to recognize and describe chemical reactions helps us understand how the world works, solve problems, and invent new products and processes.

Conclusion

Chemical reactions are vital to life and the environment. From the simple process of baking a cake to the complex systems that run the human body, chemical reactions are essential. By understanding the basics of chemical reactions, including recognizing their symbols, balancing equations, and classifying reaction types, we gain insight into the workings of our world. This foundation in chemistry prepares us to make discoveries and informed decisions in our daily lives and future scientific endeavors.


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Introduction to Chemical Reactions

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