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Chemical Reactions and Equations

Introduction

     Matter undergoes certain changes as a result of the application of energy. Glaciers melt in summer and rivers freeze in winter.

Physical Change

     A physical change is one in which the shape, size, appearance or state, of a substance may alter, but its chemical composition remains same.

Chemical Change

     A change in which the composition of a substance is altered is called as chemical change. As a result, the original properties get changed and one or more new substances are formed.

Chemical Equations

     A chemical equation is a 'balanced account of a chemical transaction.'In any chemical transaction or reaction, the number of atoms of all the participating elements will remain proportionately constant before and after the reaction

Types of Chemical Reactions

     When a chemical reaction occurs how are new substances produced? Do atoms of one element transform themselves into atoms of another element?

Combination or Addition or Synthesis Reaction

     Combination or addition or synthesis is a chemical change in which atoms or molecules of two or more substance combine to form molecules of a single new substance.

Decomposition Reaction

     A chemical reaction in which molecules of a substance break down to form simpler molecules of two or more new substances is recognized as a decomposition reaction.

Displacement or Substitution Reaction

     A substitution or displacement reaction is a chemical change in which atoms of one element replace the atoms of another element from the molecules of a compound.

Double Displacement Reaction

     Neutralisation is a type of double displacement reaction, in which, the reactants are a base and an acid, and the products are salt and water.

Oxidation Reduction

     Oxidation is a reaction in which oxygen is added or hydrogen is removed from a substance.

The Effects of Oxidation Reactions In Every Day Life

     Many metals are chemically active elements and get easily affected by substances like moisture, air, acids, etc. One must have observed iron articles that are shiny when new, but get coated with a reddish brown powder when left for some time.

Summary

     A complete chemical equation represents the reactants, products and their physical states symbolically and is a balanced account of a chemical transaction.


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Multiple Choice Questions

     



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