Grade 6
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Safety rules in chemistry laboratory  1.5. Common Laboratory Equipment and Their Uses
  2. Matter and its states  2.1. Definition of Matter  2.2. Properties of matter  2.3. States of matter  2.4. Solid state  2.5. Fluid state  2.6. Gaseous state  2.7. Plasma state  2.8. Changes in the states of matter  2.9. Melting and freezing  2.10. Evaporation and Condensation  2.11. Sublimation  2.12. Deposit
  3. Physical and chemical changes  3.1. Definition of Physical Change  3.2. Examples of physical change  3.3. Definition of Chemical Change  3.4. Examples of chemical change  3.5. Difference Between Physical and Chemical Changes  3.6. Indicators of Chemical Change
  4. Elements, Compounds, and Mixtures  4.1. Definition of the element  4.2. Classification of elements  4.3. Metals  4.4. Non metallic  4.5. Metalloids  4.6. Noble gases  4.7. Definition of compound  4.8. Properties of Compounds  4.9. Definition of Mixture  4.10. Types of mixtures  4.11. Homogeneous mixture  4.12. Heterogeneous mixtures
  5. Separation of mixtures  5.1. The need for isolation  5.2. Separation methods  5.3. Handpicking and winnowing  5.4. Filtration  5.5. Sedimentation and decantation  5.6. Evaporation  5.7. Crystallization  5.8. Distillation  5.9. Magnetic Separation  5.10. Chromatography
  6. Air and its composition  6.1. Components of air  6.2. Importance of Oxygen  6.3. The importance of nitrogen in the air and its composition  6.4. Carbon dioxide in the atmosphere  6.5. The role of water vapor and other gases in air and its composition  6.6. Properties of Air  6.7. Uses of air  6.8. Air pollution and its effects
  7. Water and its properties  7.1. Importance of Water  7.2. Sources of water  7.3. Properties of water  7.4. Water as the universal solvent  7.5. Water Purification  7.6. Water purification methods (boiling, filtration, chlorination)  7.7. Water cycle  7.8. Water conservation  7.9. Water pollution and its effects
  8. Acids, Bases and Salts  8.1. Definition of Acid  8.2. Properties of Acids  8.3. Examples of Acids  8.4. Definition of Bases  8.5. Properties of bases  8.6. Examples of Bases  8.7. Definition of Salt  8.8. Neutralization reaction  8.9. pH Scale and Indicators  8.10. Uses of Acids, Bases and Salts
  9. Introduction to the Periodic Table  9.1. History of the Periodic Table  9.2. Arrangement of elements in the periodic table  9.3. Groups and periods  9.4. Importance of periodic table  9.5. First 10 elements and their symbols
  10. Metals and Nonmetals  10.1. Properties of Metals  10.2. Properties of Non-Metals  10.3. Difference Between Metals and Nonmetals  10.4. Uses of metals and nonmetals  10.5. Corrosion of metals and its prevention
  11. chemical reactions  11.1. Introduction to Chemical Reactions  11.2. Types of Chemical Reactions  11.3. combustion reaction  11.4. Oxidation and Reduction  11.5. Simple chemical equations  11.6. Rusting of iron
  12. Fuel and energy  12.1. Types of fuel  12.2. Fossil fuels  12.3. Renewable and non-renewable sources of energy  12.4. Energy Conservation  12.5. Alternative sources of energy (solar, wind, hydropower)
  13. Plastic and fiber  13.1. Natural and synthetic fibers  13.2. Properties of plastics  13.3. Advantages and disadvantages of plastic  13.4. Recycling of plastic  13.5. Biodegradable and non-biodegradable materials

Grade 6 ↓


chemical reactions


Chemical reactions are a central concept in science that explains how substances change into different substances. Understanding chemical reactions is like unlocking the secret language of the molecules that make up our world.

What is a chemical reaction?

A chemical reaction is a process in which two or more substances, called reactants, undergo a rearrangement of atoms to form new substances called products. A common example is the reaction between vinegar and baking soda.

C 2 H 4 O 2 (acetic acid in vinegar) + NaHCO 3 (baking soda) → NaC 2 H 3 O 2 (sodium acetate) + CO 2 (carbon dioxide) + H 2 O (water)
vinegar baking soda CO2, Water

Recognizing chemical reactions

Chemical reactions can be observed through several signs:

  • Change in colour: The colour of a new substance may be different.
  • Gas production: Reactions may produce gas that is evident through bubbling or fizzing.
  • Temperature change: Reactions can release heat (exothermic) or absorb heat (endothermic).
  • Formation of a precipitate: A solid may form from the solution, indicating a reaction.

Types of chemical reactions

There are many types of chemical reactions, but we'll explore some of the most common ones:

1. Synthesis reactions

In a synthesis reaction, two or more reactants combine to form one product. For example, when hydrogen gas and oxygen gas react, they form water.

2H 2 + O 2 → 2H 2 O
H2 O2 H2O

2. Decomposition reactions

In decomposition reactions, a single compound breaks down into two or more simpler substances. For example, water can break down into hydrogen and oxygen gas.

2H 2 O → 2H 2 + O 2

3. Combustion reactions

Combustion usually involves oxygen and produces heat and light. A classic example is the burning of methane in natural gas.

CH 4 + 2O 2 → CO 2 + 2H 2 O

4. Single replacement reactions

This type of reaction occurs when one element in a compound replaces another. For example, zinc displaces hydrogen in hydrochloric acid.

Zn + 2HCl → ZnCl 2 + H 2

5. Double replacement reactions

In these reactions, parts of two compounds swap places to form two new compounds. A typical example of this is the reaction between silver nitrate and sodium chloride.

AgNO 3 + NaCl → AgCl + NaNO 3

Balancing chemical equations

A balanced chemical equation has an equal number of atoms of each type on both sides of the reaction. It is important to balance equations to accurately represent the reaction.

For example, the reaction between hydrogen and oxygen to form water can be balanced as follows:

Unbalanced: H 2 + O 2 → H 2 O Balanced: 2H 2 + O 2 → 2H 2 O
H2 H2O

Energy changes in chemical reactions

Chemical reactions involve energy transformation. Energy may be released or absorbed during the reaction.

Exothermic reactions

Exothermic reactions release energy, usually in the form of heat. A common example is the combustion of wood.

Endothermic reactions

Endothermic reactions absorb energy, which means they feel cold to the touch. An example of this is the reaction of barium hydroxide with ammonium thiocyanate.

Factors affecting chemical reactions

The rate of chemical reactions depends on several factors:

  • Temperature: Increasing the temperature usually increases the reaction rate.
  • Concentration: Higher concentration of reactants makes the reaction faster.
  • Surface area: Greater surface area allows greater contact between reactants.
  • Catalyst: Catalysts increase the rate of a reaction without consuming it.
low temperature High temperature

Chemical reactions in everyday life

Chemical reactions aren't just for scientists. They happen all around us all the time:

  • Cooking: Baking soda reacts with acids to help cakes rise.
  • Rusting: Iron reacts with oxygen and water to form rust.
  • Photosynthesis: Plants convert carbon dioxide and water into glucose and oxygen using sunlight.
6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

Conclusion

Chemical reactions are fundamental to understanding how the world works. By observing how substances interact and transform, we learn about the nature of the materials around us. Experiment safely as you explore chemical reactions and observe the incredible transformations that occur when different substances come together.


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