Chemical Reaction Type

A chemical reaction is defined as a reaction in which reactant molecules are converted into product molecules by breaking their bonds and forming new bonds. For example the combustion process (like burning a piece of paper, coal combustion, burning of candles), photosynthesis, melting of an ice, boiling of water etc. 
While a "Chemical Equation" is a mathematical statement or a representation of reactants and products by placing an arrow sign between them. 
For Example
              A  +  B  ➝  C  +  D
     Here,                                                         
           A and B are the reactants
           C and D are the products

Let us now look at various types of chemical reactions one by one in detail
  1. Synthesis reaction
  2. Decomposition reaction
  3. Single replacement reaction
  4. Double replacement reaction
  5. Combustion reaction
  6. Neutralization reaction
  7. Redox reaction
(1) Synthesis Chemical Reaction
A + B + C ➝ ABC
OR
One of the most basic type of chemical reaction is "Synthesis chemical reaction in which a single product molecule is formed by the combination of multiple reactant molecules under certain conditions". 
As shown in the above chemical equation, a product contains all the reactant atoms in their chemical formula. 
The product is always in compound form. It can be easily recognized because only one product compound is formed. 
Usually when a synthesis reaction occurs, energy is released and the reaction is exothermic in nature. In industry, synthesis reaction is used to make products in large quantity. 
For Example;
     • CaO + CO₂ ➝ CaCO₃
     • K-Cl + O₂ ➝ K-ClO₃
     • H₂O + SO₃ ➝ H₂SO₄
     • 2Na + Cl₂ ➝ 2NaCl

(2) Combustion Reaction
A + burning (by air, O₂) ➝ products
OR
......"A reaction of a fuel with oxygen, producing energy in the form of heat heat/light"......

A combustion reaction involves air (mainly, O₂) as a reactant molecule. This type of chemical reaction emits energy in the form of heat and light. 
"It contains a flammable substance which burns in the presence of oxygen (O₂) and forms an oxidised product". Here, oxygen acts as an 'oxidizer'. 
The combustion reaction itself is quite exothermic as it releases energy in the form of heat. Many combustion reactions occur with hydrocarbons and the product of hydrocarbon combustion is always carbon dioxide and water (CO₂ and H₂O). As it releases very large amount of heat energy, many hydrocarbons are used as a fuel. 
For Example;
• 2Mg + O₂ ➝ 2MgO + 🔥(heat) 
• CH₄ + O₂ ➝ CO₂ + H₂O 
• C₃H₈ + 5O₂ ➝ 3CO₂ + 4H₂O
• C + O₂ ➝  CO₂ 
• Burning of Wood or Coal for the household purposes. 
• Combustion of butane ( found in lighters) 
Burning of petrol and diesel for vehicles. 

(3) Decomposition Reaction
ABC ➝ A + B + C
"A decomposition reaction is defined as a reaction in which a single compound breaks down into multiple components as shown in the above chemical equation". 
Decomposition reactions are useful where we have to extract metals from their ores. (like zinc from calamine, aluminum from bauxite etc.)
Most decomposition reactions are endothermic, meaning that it requires energy in the form of heat and light but not all decomposition reactions are Endothermic. 
"Decomposition are the reverse of synthesis". 
A decomposition reaction can be both Endothermic or exothermic.
For Example;
• CaCO₃ ➝ CaO + CO₂
• 2NaOH ➝ 2Hg + O₂
• 2KClO₃ ➝ 2KCl + 3O₂
• H₂CO₃ ➝ H₂O + CO₂
• Digestion of food in our body is done by many decomposition reaction. 

Decomposition reactions are of different types and these are -
a. Thermal decomposition reaction in which we use thermal energy to activate a reaction. It is endothermic in nature. For example- decomposition of CaCO₃.
b. Electrolytic decomposition reaction in which we use electrical energy for decomposition or to activate a reaction. For example- decomposition of water. 
c. Photo-decomposition reaction in which the reactant decomposes into its components by absorbing energy from photons or simply light energy. For example, decomposition of ozone into oxygen. 

(4) Single Replacement Reaction
A + BC ➝ AC + B 

As shown in the chemical equation above, "A single substitution reaction or single replacement reaction is defined as a reaction in which one element (say, "C") in a compound (say, "BC")is replaced by another element (say, "A") or same element". 
Same element means a metal replaces a metal, a non-metal replaces a non-metal. In this, there is one element as a reactant and another reactant as a product. 
For example;
      • 2HCl + Zn ➝ Zn-Cl₂ + H₂ 
      • 2NaCl + F₂ ➝ 2NaF + Cl₂ 
      • CaBr₂ + F₂ ➝ CaF₂ + Br₂  
      • Mg + Cu(NO₃)₂ ➝ Mg(NO)₂ + Cu
      • 2Na + 2H₂O ➝ 2NaOH + H₂
      • 2Fe₂O₃ + 3C ➝ Fe + CO₂

(5) Double Replacement Reaction
A⁺B⁻ + C⁺D⁻ ➝ A⁺D⁻ + C⁺B⁻
OR

As shown in the above equation, the double replacement reaction or dual substitution reaction is defined as a reaction in which two reactant compounds react with each other and their positively and negatively charged ions switch places, forming entirely two different compounds. 
Usually, a double replacement reaction results in the precipitate formation. There are 'Three types of double replacement reactions precipitation, neutralization and gas formation'. 
Most double substitution reactions occur between ionic compounds that dissolve easily in water. 
For Example;
(a) Ag-NO₃ + Na-Cl ➝ Ag-Cl + NaNO₃ 
(b) Formation of precipitate,  
    2KI + Pb(NO₃)₂ ➝ 2KNO₃ + Pb-I₂ ↓
(c) Formation of a gas, 
     Na₂S + 2HCl ➝ 2NaCl + H₂S ↓
(d) Cu-Cl₂ + 2AgNO₃ ➝ Cu(NO₃)₂ + 2AgCl↓
(e) BaCl₂ + Na₂SO₄ ➝ BaSO₄ + 2NaCl

(6) Neutralization Reaction
                 AB   +   CD    ➝    AD   +   BC
               Acid      Base         Salt      water

Neutralization reaction is generally a type of double replacement reaction in which an acid and a base reacts with each other and neutralizes (means that the pH of the solution is around 7) into salt and water as a product.Here, salts are ionic compounds consisting of an anion from an acid and the cation from a base. It is also known as "Quantitative Reaction". 

There are mainly four types of chemical reaction based on how strong acid and base are or how weak acid and base are;
(1) Strong acid + Strong base ➝ ph=7
(2) Strong acid + Weak base ➝ ph<7
(3) Weak acid + Strong base ➝ ph>7
(4) weak acid + weak base ➝ ph<7 or ph≥7
Examples Are;
     • H₂SO₄ + 2NaOH ➝ Na₂SO₄ +2H₂O
     • 2HCl + Ca(OH)₂ ➝ Ca-Cl₂ + 2H₂O
     • H₂CO₃ + 2LiOH ➝ Li₂CO₃ + 2H₂O
     • H₃PO₄ + 3NaOH ➝ Na₃PO₄ + 3H₂O 

(7) Redox Reaction Or Oxidation-Reduction Reaction
A + B ➝ A⁺ + B⁻
As shown in the above chemical equation, "A redox reaction is defined as a reaction in which the reactant changes their oxidation states by losing or gaining electrons". In this reaction, both the oxidation and reduction reactions occur simultaneously. The substance which is getting reduced during the reaction by accepting electrons is called as an "Oxidizing Agent" while the substance which is getting oxidized during the reaction by losing electrons is called as "Reducing Agent". 

Fig:- Redox Reaction

"A reaction in which electrons are transfer between the reactants is called as Redox reaction". There is no net change in the number of electrons in a redox reaction. Redox reactions are comprised of two parts, 
Reduction- Oxidation state decreases by gaining of electrons. 
Oxidation- oxidation state increases by losing of electrons. 
For Example;
(A) Cu-SO₄ + Zn⁰ ➝ Cu⁰+ Zn-SO₄ 
Here, 
    Cu²⁺ ➝ Cu⁰ - Reduction by gaining electrons
    Zn⁰ ➝ Zn²⁺ - Oxidation by losing electrons
Both the oxidation and reduction reaction occurs simultaneously, hence it is called as Redox reaction. 
(B) CH₄ + 2O₂ ➝ CO₂ + 2H₂O
Here, 
   1 C atom is oxidised from -4 to +4
   4 O atoms are reduced from 0 to -2
 While hydrogen atom remains unchanged. 

(C) 3MnO₂ + 4Al ➝ 3Mn + 2Al₂O₃  
Here, 
    Mn⁴⁺ ➝ Mn⁰ - Reduction by gaining electrons
    Al⁰ ➝ Al³⁺ - Oxidation by losing electrons



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