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 → Types of Chemical Reactions ↓


Combination Reactions


Chemistry is a fascinating subject that explains how everything around us is made up of tiny particles called atoms and molecules. One interesting type of chemical reaction is called a combination reaction. Let's dive deeper into this topic and learn what combination reactions are, how they work, and see examples of them in action.

What is a combination reaction?

A combination reaction, also called a synthesis reaction, is a type of chemical reaction in which two or more substances combine to form a new, single product. The substances that combine may be elements or compounds.

In a combination reaction, you start with several reactants and end up with one product. This can be represented in general terms as follows:

A + B → AB

Here A and B represent reactants, and AB is the product formed by the combination of A and B.

Examples of combination reactions

Example 1: Formation of water

A well-known example of a combination reaction is the formation of water from hydrogen gas and oxygen gas. The chemical equation for this reaction is:

2H 2 + O 2 → 2H 2 O

In this reaction, hydrogen (H 2) and oxygen (O 2) gases react to form water (H 2 O), which is a liquid compound.

H2 O2 H2O

Example 2: Formation of carbon dioxide

Another common example is the formation of carbon dioxide when carbon burns in the presence of oxygen:

C + O 2 → CO 2

In this case, carbon (C), a solid element, reacts with oxygen gas (O 2) to form carbon dioxide gas (CO 2).

C O2 CO2

Viewing combination reactions

To better understand combination reactions, let's use a simple diagram to visualize what happens in one. When two gases, such as hydrogen and oxygen, combine during a combination reaction, they form a new compound, such as water. Imagine the molecules coming together, almost as if they are fitting puzzle pieces together to form a bigger picture.

H2 O2 H2O

More examples of combination reactions

Combination reactions are all around us. Here are some more examples that show how common and important these reactions are:

Example 3: Formation of sulfur dioxide

Sulfur dioxide is formed when sulfur reacts with oxygen:

S + O 2 → SO 2

In this reaction, solid sulfur (S) combines with oxygen gas (O 2) to form sulfur dioxide gas (SO 2).

Example 4: Formation of ammonia

Ammonia is formed by the combination of nitrogen and hydrogen:

N 2 + 3H 2 → 2NH 3

In this synthesis reaction, nitrogen gas (N 2) and hydrogen gas (H 2) react to form ammonia gas (NH 3).

Example 5: Formation of metal oxides

Metals that react with oxygen often form metal oxides. For example, when magnesium burns in air, it reacts with oxygen to form magnesium oxide:

2Mg + O 2 → 2MgO

Here, solid magnesium (Mg) combines with oxygen gas (O 2) to form solid magnesium oxide (MgO).

Classifying combination reactions

Combination reactions can also be classified based on the type of reactants involved:

1. Reaction of elements

These reactions involve two or more elements. For example:

Fe + S → FeS

Iron (Fe) combines with sulfur (S) to form iron sulfide (FeS).

2. Reaction of compounds

Sometimes, two compounds can combine to form a new compound. For example:

CaO + CO 2 → CaCO 3

Calcium oxide (CaO) reacts with carbon dioxide (CO 2) to form calcium carbonate (CaCO 3).

3. Reaction of an element with a compound

An element and a compound can also combine to form another compound. Example:

2SO 2 + O 2 → 2SO 3

Sulfur dioxide (SO 2), a compound, combines with oxygen (O 2), an element, to form sulfur trioxide (SO 3).

Importance of combination reactions

Combination reactions are important in many natural processes and industrial applications. Here are some reasons why they are important:

  • Natural processes: Many environmental and biological processes involve combination reactions. For example, when plants photosynthesize, water and carbon dioxide combine to form glucose, a vital process for life on Earth.
  • Industrial processes: Many materials, such as ammonia and sulfuric acid, are produced using combination reactions. These compounds serve as key components in fertilizers, cleaning agents, and other products.
  • Energy production: Combustion, which is an exothermic combination reaction, is used to produce energy in engines and power plants. For example, burning methane gas combines with oxygen, releasing energy as heat:
CH 4 + 2O 2 → CO 2 + 2H 2 O

Conclusion

Combination reactions are an important aspect of chemistry and play an essential role in both natural and industrial processes. Understanding how these reactions occur, what conditions they require, and what products they form helps us understand the chemical changes that support life and modern technology.

By exploring different examples and visual models, we can better understand how reactants come together to form new products in combination reactions. In many ways, these reactions underscore the interconnectedness of chemical processes, showing how simple reactants merge to form more complex compounds.

The next time you see a car moving or a plant growing, remember that combined reactions can play a key role in making these everyday miracles happen.


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Combination Reactions

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