Chemical changes


 
 
Concept Explanation
 

Chemical Changes

Chemical Change:

A chemical change occurs when two or more chemical substances react to produce new substance with a different set of properties. It is permanent which cannot be reversed. Examples:

  • Reddish – Brown Decomposition on Iron Objects: Iron reacts with atmospheric oxygen in the presence of moisture to form a reddish-brown layer of iron oxide. This layer is called rust and process is called rusting. Oxygen and water are the two essential conditions for rusting of iron. 
  • Browning of Vegetables and Fruit Surfaces: When we exposed the cut surface of a brinjal to the air for some time, the surface has turned brown, due to a chemical reaction between certain compounds present in brinjal and atmospheric oxygen to produce a brown colour pigment “melanin” that cause browning of the surface. 
  • Reaction Between Vinegar and Baking Soda: Vinegar + Baking soda  rightarrow  carbon dioxide + water + other substances. To test carbon dioxide gas, Carbon dioxide + lime water(calcium hydroxide)  rightarrow   calcium carbonate + water.
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    Sample Questions
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    Question : 1

    When Magnesium is burnt, heat and light are produced .The burning of Magnesium is a :

    Right Option : C
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    Explanation
    Question : 2

    A chemical change may involve :

    Right Option : D
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    Explanation
    Question : 3

    When iron rusts, it is an example of:

    Right Option : B
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    Explanation
     
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