Introduction to Chemical Reactions

Table of Contents

CHEMICAL REACTIONS AND EQUATIONS CLASS 10

INTRODUCTION

  • What is a chemical reaction?    
  • Simply, it is a chemical change!

Examples  of chemical change from our daily life

    • Souring of milk
    • Formation of curd from milk
    • Cooking of food
    • Digestion of food in our body
    • Process of respiration
    • Fermentation of grapes
    • Rusting of iron etc.

chemical reaction

  • In all these reactions there is a change that occurs, that is a “chemical change”.
  • Therefore we can say that a chemical reaction is a chemical change.

A chemical reaction may be defined as the process of reacting one or more substances to give a new substance. The reacting substances are called Reactants and the new substance formed is called the Product.

  • The substances which take part in a chemical reaction are called reactants.
  •  The new substances produced as a result of a chemical reaction are called products.

How will you know to whether a chemical reaction has taken place or not

  •   When a chemical reaction occurs there is a change in 
    • Color
    • temperature
    • state
    • Evolution of gas

Example of Chemical Reaction

ACTIVITY 1.1 

  • Take 2 cm long Magnesium ribbon clean it with sandpaper.
  • Hold it with a pair of tongs, burn it with a burner and collect the ashes in a watch glass.
  • What do you observe?
  • The ribbon burns with a bright white light.
  • Intense heat is also produced in this reaction.
  • Here, when magnesium burns, it reacts with the oxygen found in the air to form powdery ash called magnesium oxide.
  • The magnesium ribbon (reactant) burns with a dazzling flame and changes into a white powder.
  • This powder is magnesium oxide(product).
  • It is formed due to the reaction between magnesium and air.

representation of chemical equation in words

ACTIVITY 1.2 

Reaction of lead nitrate with potassium iodide

  • Take lead nitrate solution in a beaker
  • add potassium iodide into this
  • what do you observe?
  • The yellow color is observed.

 

When sulphur dioxide gas is passed through potassium dichromate solution, the orange colour of potassium dichromate solution changes to green

CHEMICAL EQUATIONS

Representation of chemical reaction using symbols and formulae of the substances is called Chemical Equation.                         

  • Example: A + B → C + D                                                                                           
  • In this equation, A and B are called reactants, and C and D are called the products.
  • The arrow shows the direction of the chemical reaction
  • e. g; A word equation can be represented as ;
  • Zinc + Sulphuric acid → Zinc sulfate + Hydrogen
  • We can change this word equation into a chemical equation by writing the symbols and formulae of the various substances in place of their names.

Important Questions on

Chemical reactions are the processes in which new substances with new properties are formed.

During respiration, Energy is released. Hence it is a chemical reaction.

  • When potassium iodide solution is added to a solution of lead nitrate, then a yellow precipitate of lead iodide is formed.
  •  
  •  The chemical reaction between sulphuric acid and barium chloride solution is characterised by the formation of a white precipitate of barium sulphate.

Zinc metal reacts with dilute sulphuric acid to form zinc sulphate solution and hydrogen gas.

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