chemical reaction and Types of chemical reactions

 

Types of chemical reactions

A chemical reaction is the process to involve the breaking and making or formation  of chemical  bonds between atoms to produce new substances is known as chemical reaction.

A chemical reaction is the chemical transformation in which  one type of substance which is reactants reacts chemically and converts  into a new substances which is products.

There are different types of chemical reaction :--

 

1. Combination  reaction:---

                                           In this combination reaction, single products is formed from two or more reactants is known as combination reactions.

Combination reactions is also called as synthesis reaction

Example :--

        CaO (s) + H₂O (l)    →         Ca(OH)₂ (aq)   + heat

 

Here, calcium oxide and water Is combined to form a single product calcium hydroxide.

 

Burning of coal:--

 C (s) + O₂(g)  →       CO₂(g)

 

Formation of water from H₂ (g)and O₂ (g)

2H₂(g)   +O₂ (g)   →   2H₂O (l)

 

 

Here, we see that when two or more substances (elements or compounds ) combines to form a single products , the reaction is also called combination reactions.  

 

 

 

 

 

2. Oxidation and reduction:--

                                                             The chemical reactions in which Oxidation and Reduction occurs simultaneously is called as redox reaction. Or we can say that one substance in reactants gets oxidised while the other gets reduced during a chemical reaction. Such reaction are called as oxidation- reduction or redox reactions.

Neither oxidation nor reduction can occur takes place alone.

Redox reaction may involve the transfer of an electrons between chemical species.

       Zn + 2H⁺     Zn²⁺  + H₂

Oxidation means addition of the oxygen. And if the substance gains oxygen or losses of hydrogen  during a chemical reaction, it is said to be oxidised.

Reduction means the addition of the hydrogen or removal of oxygen. And if the substance loses oxygen during a chemical reaction, it is said to be reduced.

 

                   CuO  + H₂        →         Cu        +       H₂O

 

The surface of copper powder becomes coated with black copper (II) oxide. Why the black substance formed?

The surface of copper powder becomes coated with black copper (II) oxide.  the black substance is formed because oxygen is added to copper and copper oxide s formed.

   2Cu    +   O₂           →       2CuO  

 

If the Hydrogen gas is passed over this heated material (CuO), the black coating on the surface turns brown as the reverse reaction takes place and copper is obtained.

  CuO  + H₂     →                     Cu   +   H₂O

 

 

Some more examples are:--

 

ZnO    +C →   Zn + CO

Here, carbon gets oxidised to CO and ZnO gets reduced to Zn

 

MnO₂   +  4HCl    →            MnCl₂       +2H₂ O   + Cl₂

 

Here, HCl gets oxidised to Cl₂  whereas MnO₂ gets reduced to MnCl₂.

 

From the above example we can say that

Oxidation means addition of the oxygen. And if the substance gains oxygen or losses of hydrogen  during a chemical reaction, it is said to be oxidised.

Reduction means the addition of the hydrogen or removal of oxygen. And if the substance loses oxygen during a chemical reaction, it is said to be reduced.

 

3. Double displacement Reaction:--

                                                                        Such reaction in which there is an exchange of the ions between the reactants are called double displacement reactions.

Precipitation reaction:--

                                             In the chemical reaction, any reaction that produces a precipitate can be called a precipitation reaction.

Na₂SO₄ (aq) +   BaCl₂ (aq)  →          BaSO₄ (s)  +  2NaCl (aq)

 During such reaction, a white substance is formed which is insoluble in water. This insoluble substance formed is called as a precipitate.

 

4. Displacement reaction:--

                                                             In the chemical reaction, reactive metals gets  displaced or removed another metal or less reactive metals from its solution. 

Why does the iron nail become brownish in colour and the blue colour of copper sulphate solution fades?

Fe (s) + CuSO₄ (aq)   →     FeSO₄ (aq)   +  Cu (s)

In this reaction, iron gets  displaced   or removed another element, copper, from copper sulphate solution.

Other example are :--

Zn (s) + CuSO₄ (aq)    →    ZnSO₄ (aq)   +  Cu (s)

Zinc is more reactive metal than copper they displace copper from its compound

Pb (s)  +  CuCl₂ (aq)  →        PbCl₂ (aq)    +   Cu (s)

Lead  is more reactive metal than copper they displace copper from its compound.

 

5.                   Decomposition reaction:--

                                                            the decomposition reaction is the chemical reaction in which a single reactants breaks down to give simpler products is known as decomposition reactions.

 

2 FeSO₄ (s)    →    Fe₂O₃ (s)  +  SO₂ (g)   +  SO₃ (g)

 Here, green colour of the ferrous  sulphate crystals has changed. And the smell is odour of burning sulphur.we observer that a single reactants breaks down to give simpler products. During the decomposition reaction, the ferrous sulphate crystals (FeSO₄ , 7H₂O ) lose water when heated and the colour of the crystals changes.

It then decomposes to ferric oxide Fe₂O₃ (s)  , sulphur dioxide SO₂ (g)     and sulphur trioxide SO₃ (g).

ferric oxide is solid but sulphur dioxide SO₂ (g)  and sulphur trioxide SO₃ (g) are gases.

 

CaCO₃ (s)   →     CaO (s)      CO₂(g)

Here , decomposition reaction takes place. Calcium carbonate is decomposed into calcium oxide and carbon dioxide on heating. Calcium oxide is also called as lime or quick lime. It is used in various industry purposes like manufacturing of the cements

 

 

 

 

 

6. Exothermic chemical reaction:--

                                                                       Exothermic chemical reaction is the chemical reaction in which heat is released along with the formation of products are called exothermic chemical reactions. Decomposition of the vegetables matter into the compost is also example of the exothermic reaction.

Examples:--

Burning of natural gas:--

                   CH₄ (g)     +     2O₂ (g)   →     CO₂ (g)  +  2H₂O  (g)

 

Respiration is an exothermic process

Energy is required to keep alive. We get this energy from the food. During the digestion of the food , food is broken down into simpler substances or compounds.  For example , rice ,potatoes contains carbohydrates. These carbohydrates are broken down into the form of the glucose. These glucose combines with the oxygen in the cells of our body and provides energy. This is also known as respiration.

The chemical reaction of respiration :--

C₆H₁₂O₆ (aq)   +  6O₂ (aq) →  6CO₂ (aq)   +  2H₂O (l)   +energy

 

 

Endothermic reaction:--

                                             Endothermic reaction is the chemical reaction in which energy is absorbed is known as endothermic reaction. Here decomposition reactions requires energy either in the form of the heat, light or electricity for breaking down the reactants.

 

2AgCl (s)    →  2Ag (s)    +Cl₂

Here, silver chloride turns into grey in sunlight. This is due to the decomposition of the silver chloride into silver and chloride by the help of light.