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Introduction to Chemical Reactions

Aug 24, 2022

Key Concepts

  • Chemical changes
  • Physical changes
  • Chemical reaction
  • Representation of chemical reaction


The difference observed between the original form of an object/particle/material/matter and the final form is defined as change. Some of the general examples of changes that we see in our daily life are: making airplanes from a sheet of paper, growth of nails, hair or body, and cooking of food. 

Based on the change from the initial to the final form, and the changes occurring, the properties changes are classified into two types: 

  1. Physical changes 
  2. Chemical changes 

Physical Changes:  

Changes that occur in the physical properties of objects or materials or substances are called physical changes. Some of the examples of the physical changes are tearing of paper, melting of ice, formation of ice, chopping of wood. 

Characteristics of physical changes: 

  • In the process of physical change, a new substance or material is not formed.  
  • Physical change is observed only in the physical state. 
  • Physical changes are mostly temporary and reversible. It means that a product can be brought back to its initial form after it goes under some physical change. 

Chemical Changes: 

Changes that occur in the chemical properties of a substance are called chemical changes. Some best examples we see in our daily life are cooking food, burning of wood, and explosions of fireworks. 

Characteristics of the chemical changes: 

  • In the process of chemical changes, a new substance is formed. 
  • In the chemical change, the new composition is formed. 
  • Most of the chemical changes are permanent and irreversible. 
Chemical Changes

What are chemical reactions? 

Chemical reaction: 

When a chemical change occurs in a substance we can say that a chemical reaction has taken place. Some of the examples for the chemical reaction are rusting of iron, cooking of food, and combustion. 

chemical reactions

How to identify the chemical reaction? 

We can identify the chemical reaction by observing:  

  • Change in color 
  • Change in state 
  • Change in temperature 
  • Evolution of gas 


Take a magnesium ribbon. When the magnesium ribbon is burnt in the presence of air it forms some white colored powder. The magnesium ribbon is a silvered metal ribbon, it turns into powder. It changes its state and color. When the ribbon is burnt in air it releases the white colored flames and turns into white powder. 

Some other examples are fermentation, routine of eggs, ripening of fruits. 

How do we represent the chemical reaction? 

Chemical reaction is represented by writing the names of initial substances and the names of the final substances obtained. The chemical reaction is represented by the equation. The word equation is the equation representing the initial and final products of the chemical reaction in a single equation. The word equation represents the substances before and after the reaction in word form separated by an arrow mark. 


Take the example discussed earlier, the burning of magnesium in the presence of air to form magnesium oxide. In the equation form we write the above reaction as follows: 


Magnesium + Oxygen → Magnesium oxide 

Some other chemical reactions that we regularly see or observe are the change of milk into curd by the process of fermentation, cooking food. All these reactions are external and there are some internal chemical reactions, internal here means the reactions in our body. The process of digestion, growth of the organs and the human body. The chemical reactions that we can see in the plants are the process of photosynthesis, and respiration in plants. 

Applications of chemical reaction: 

Chemical reactions are very useful as they help us in producing the required results like digestion of food, and provide energy. In producing the food from plants, and the metabolic reactions in the living things. 

Drawbacks of chemical reaction: 

Chemical reactions have a positive side, however there are some drawbacks as well. Some of them are reactions like rusting makes the iron weak and it may cause a lot of damage, burning of the wood or trees causes deforestation and pollution. 



  • Changes happen around us everyday, and can be two types:
    • Physical
    • Chemical
  • Chemical changes are also called chemical reactions which are permanent and result in the formation of new substances.
  • Physical changes are temporary and form no new substances.
  • Chemical reactions are represented by a word equation.


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