Chemical reaction and equation

  Chemical reactions-

 The transformation of chemical substance into a new chemical substance by making and breaking of bonds between different atoms is known as Chemical Reaction.

 Signs of a chemical reaction

These factors denote that a chemical reaction has taken place- change of state of substance, change of color of substance,evolution of heat, absorption of heat, evolution of gas and evolution of light.

Chemical Equation: 

 The representation of chemical reaction by means of symbols of substances in the form of formulae is called chemical equation. 

E.g. - H2 + O2 ⇒ H2O

                       Balanced Chemical Equation: 

A balanced chemical equation has number atoms of each element equal on both left and right sides of the reaction.

                           

      

*Note- According to Law of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction. To obey this law, the total mass of elements present in reactants must be equal to the total mass of elements present in products.

                            

  Types of Chemical Reactions-

 I.  Combination- When two elements or one element and one compound or two compounds combines to give one single product.

                     

II.  Decomposition- Splitting of a compound into two or more simple products.

                

 III.  Displacement- It takes place when a more reactive metal displaces a less reactive metal.

               

  IV.  Double displacement- Reactions in which ions are exchanged between two reactants forming new compounds are called double displacement reactions.

                                  

 V.  Precipitation- The insoluble compound called precipitate forms in this reaction.

                              

 VI.  Exothermic- Reactions which produce energy are called exothermic reaction. Most of the decomposition reactions are exothermic.

                          

 VII.  Endothermic- Reactions which absorb energy are called endothermic reaction. Most of the combination reactions are endothermic.

        

                            

 VIII.  Oxidation: Gain of oxygen or removal of hydrogen or metallic element from a compound is known as oxidation

                                            .

IX.  Reduction: Addition of hydrogen or removal of oxygen from a compound is called reduction.

                                  

 X.  Redox- A chemical reactions where oxidation and reduction both take place simultaneously are also known as redox reaction.

                             Eg - NaOH + HCl ⇒ NaCl + H2O

   

                           

6.  Rusting- When iron reacts with oxygen and moisture forms a red substance called rust.

                               

                      

                             

7.  Rancidity- Oils and fats when get oxidized on exposure to air show a change in taste and smell.

8.  Corrosion- Metals when attacked by oxygen, water, acids, gases, present in air changes its surface which is called corrosion.