Chemical Change or Reaction

A change in which the chemical composition changes and a new substance is obtained with properties different from those of the original substances is called a chemical change or reaction.

Key Points:
- During a chemical reaction, bonds between atoms are broken and new bonds are formed.
- The atoms are rearranged to create new substances with different properties.
- Chemical reactions are usually accompanied by the release or absorption of energy in the form of heat, light, or sound.
- Some signs of a chemical change include color change, formation of a precipitate, evolution of gas, and change in temperature.

Examples of Chemical Changes:
1. Burning of wood: Wood undergoes a chemical reaction with oxygen in the air to produce ash, carbon dioxide, and water vapor.
2. Rusting of iron: Iron reacts with oxygen and water in the environment to form rust, which is a different substance with different properties than iron.
3. Digestion of food: The food we eat undergoes chemical reactions in our body to be broken down into nutrients that our body can use.

Importance of Chemical Changes:
- Chemical changes are crucial for various industrial processes, such as manufacturing plastics, fertilizers, and pharmaceuticals.
- Understanding chemical reactions helps scientists develop new materials and improve existing products.
- Chemical changes also play a significant role in biological processes, such as metabolism and photosynthesis.

In conclusion, chemical changes involve the transformation of substances into new materials with different properties. These reactions are fundamental in our daily lives and have a significant impact on various aspects of science and industry.