What is Chemical Reaction? And Type of Chemical Reaction

Chemical reaction: The process in which some particular substance inter acts with each other to form new substance with those new properties.

Properties of chemical reaction:-

(1) In chemical reaction these must be a chemical change.

(2) In chemical reaction breaking of old chemical bond and formation of new chemicals bond takes place.
examples:-
                          H₂+Cl₂ → 2(HCl)

H-H+Cl-Cl → 2(H-Cl)

2H₂+O₂ → 2H₂O

2(H-H)+(O=O) → 2(H-O-H)

N₂+3H₂ → 2NH₃

(3) In chemical reaction rearrangement of atoms happens.

examples:-

                          H₂+Cl₂ → 2(HCl)

H-H+Cl-Cl → 2(H-Cl)

{In H-Cl bond rearrangement}

Example of chemical reaction:-

• Souring of milk.
• Formation of curd from milk.
• Cooking of food.
• Digestion of food in our body.
• Process of respiration.
• Rusting of iron.
• Burning of candle wax.
• Ripening of fruits.
• Burning of magnesium in air.etc...

NOTE:- When a magnesium ribbon is heated in the presence of air with a dazzling white flame to form a white powder called magnesium oxide.

Mg+O₂ → MgO

Mg (Magnesium) as form of ribbon or wire. 

O₂(Oxygen) from air.

MgO (Magnesium oxide) White Powder.

➣ Basic magnesium carbonate is a mixture of magnesium carbonate and magnesium hydroxide.

➣ Burning of magnesium ribbon or wire in air then produce white light. The light harmful to the eyes.

Parts of chemical reactions:-

There are three parts;

(1) Reactants.

(2) Products.

(3) Catalyst.

(1) Reactants:- Those substances which directly participates in chemical reaction is called Reactants.

(2) Products:- Those substances which are produced as a result of chemical reaction is called Products.

examples:-

                         N₂+3H₂ → 2NH₃

2H₂+O₂ → 2H₂O

NH4Cl → NH₃+HCl
CaCO₃ → CaO+CO₂

Zn+CuSO₄ → ZnSO₄+Cu

LHS side are Reactants and RHS side are Products.

(3) Catalyst:- Those chemical substances which do not participates directly in chemical reaction but effect the rate of chemical reaction is called Catalyst.

Types of Catalyst:-

(i) Positive Catalyst:- Reaction rate increasing Catalyst.

(ii) Negative Catalyst:- Reaction rate decreasing Catalyst.

Symptoms or characteristics of chemical reaction:

The easily observable changes which take place as a result of chemical reaction are known as characteristics of chemical reaction.

There are following characteristics of chemical reaction:-

(1) Evolution of Gas.

(2) Change of Colour.

(3) Formation of a precipitate.

(4) Change of temperature/energy.

(5) Change of state.

(1) Evolution of Gas:- some chemical reaction are identified by emission of sertain gases as a product of the reaction.

examples:-
                   CaCO3 → CaO+CO2 

Zn+2HCl [diluate] → ZnCl₂+H₂

H₂SO₄+Cu → CuSO₄+H₂

Mg+2HCl → MgCl₂+H₂

Fe+H₂O → Fe₃O₄+H₂

(2) Change of Colour:- Some chemical reactions are characterised by change of colour after the completion of reaction it means either product has different colour from reactant or product becomes colour less from colour full reactant.

examples:-

CaO+H₂O → Ca(OH)₂+CO₂

CaO → white

Ca(OH)₂ → colourless

Cu+H₂SO₄ → CuSO₄+H₂

Cu+H₂SO₄ → Reddish brown

CuSO₄ → blue

FeSO₄+Mg → MgSO₄+Fe

FeSO₄ → green

MgSO₄ → colourless

(3) Formation of a precipitate:- The insoluble and heavy solid substance obtained and the bottom of the container as a product of the reaction is called as precipitate. It is written as 'ppt'.

examples:-

KI+PbNO₃ → KNO₃+PbI

 (yellow ppt)

AgNO₃+KCl → KNO₃+AgCl 

(white ppt)

K₂CrO₄+Pb(NO₃)₂ → PbCrO₄+2KNO₃ 

(yellow ppt)

H₂SO₄ (diluate)+BaCl₂ → BaSO₄+2HCl

(4) Change of temperature/energy:-  In some particular chemical reaction certain amount of change of temperature happens. In some cases the temperature of the system increases while in some cases the temperature decreases.

examples:-

CaO+H₂O → Ca(OH)₂+heat energy

Zn+2HCl(diluate) → ZnCl₂+H₂+ heat energy

NH₄Cl+H₂O → NH₄Cl(aq)+heat energy

(5) Change of a state:-  Some chemical reactions are identified by change of state between reactant or products.

examples:-

 CaCO₃ → CaO+CO₂

2H₂+O₂ → 2H₂O

Types of chemical reactions:-

(1) Combination Reaction/Synthesis.

(2) Decomposition Reactions.

(3)  Displacement Reactions.

(4)  Double displacement Reactions.

(5) Oxidation and Reduction Reactions.

(1) Combination Reaction:→ The type of chemical reaction in which two or more substance react chemically with each other to produce a single substance having different properties is known as Combination reaction.

example:-

N₂+3H₂ → 2NH₃

CaO+CO₂ → CaCO₃

H₂O+CO₂ → H₂CO₃

C+O₂ → CO₂

2Mg+O₂ → 2MgO

(2) Decomposition Reaction:→ The type of chemical reaction is a single substance splits into two or more substances on the application of external energy is known as Decomposition reaction.

There are three types of decomposition reaction:-

• (i) Thermal decomposition
• (ii) Electrical decomposition
• (iii) Photo decomposition

(i) Thermal decomposition:- The decomposition by heat energy.

eg:- 

CaCO₃ → CaO+CO₂

NH₄Cl → NH₃+HCl

(ii) Electrical decomposition:- The decomposition by application of electrical energy.

eg:-  

2NaCl → 2Na+Cl₂

(iii) Photo decomposition:- The decomposition by light energy.

eg:- 

2AgCl → 2Ag+Cl₂

2AgBr → 2Ag+Br₂

(3) Displacement Reaction:→ The type of chemical reaction in which any particular element takes the position of another element of their compound is called displacement reaction.

example:-

CuSO₄+Zn → ZnSO₄+Cu(solid)

CuSO₄+Mg → MgSO₄+Cu

CuSO₄+Fe → FeSO₄+Cu

NOTE:-  A+B-X → A-X+B

[ A is more reactive than B ]

A+B-X → No reaction 

[ B is more reactive than A ]

(4) Double Displacement Reaction:→ The type of chemical reaction in which the exchange of cation and anion between two different compounds occurs to form new type of product is called Double displacement reaction.

example:-

AgNO₃+NaCl → AgCl+NaNO₃

AlCl₃+3(NH₄)OH → Al(OH₃)+3(NH₄)Cl

BaCl₂+CuSO₄ → BaSO₄+CuCl₂

Pb(NO₃)₂+KI → PbI₂+2KNO₃

NaOH+HCl → NaCl+H₂O

(5) Oxidation and Reduction Reaction:→ (Redox reaction)

Oxidation:- Oxidation is a chemical reaction which has following characteristics;

• The chemical combination with oxygen or any other electro-negative elements.
• The removal of electro-positive elements.
• The process of lossing electron.

Reduction:-  Reduction is a chemical reaction in which has following characteristics;

• The chemical combination with hydrogen or any other electronegative elements.

• The removal of oxygen or any other electropositive elements.

• The process of gaining of electron.

example:-

CuO+H₂ → Cu+H₂O

In above example Addition of oxygen: oxidation and 

Removal of Oxygen: Reduction.

Some important definition:

Oxidising agent (Oxidant):→ The chemical substance which is reduced to support the oxidation process is called as oxidising agent. 

Reducing agent (Reductant):→  The chemical substance which is oxidising to support the reduction process is called as Reducing agent. 

Electropositive element:→ Those element which has capacity to lose electron to form cation is known as electropositive element.

example:- Generally all metals.

Electronegative element:→ Those element which has capacity of expect electron to form anion is known as electronegative element.

example:- Generally all non metals.

Endothermic Reaction:→ The reactions in which heat is absorbed are called endothermic reaction.

example:- 

N₂+O₂ → 2NO

H₂+I₂ → 2HI

Exothermic Reaction:→ The reactions in which heat is evolved are called exothermic reaction.

example:- 

C+O₂ → CO₂

2H₂+O₂ → 2H₂O

Reversible Reaction:→  The reactions which take place as per conditions in both direction are called reversible reaction.

example:-

3Fe+4H₂O(stream) ⇌ F₃O₄+4H₂

Irreversible Reaction:→ The reactions Which produced in only one direction are called Irreversible reaction.

example:- 

C+O₂ → CO₂

H₂+O₂ → H₂O

Effects of Oxidation reaction in every life:

There are two effect following:-

(1) Corrosion:→ The process in which metals are eaten up gradually by the action of air moisture or a chemical on their surface is called corrosion.

example:-  Rusting of iron metal is the most common form of corrosion.

Rusting of Iron (Rust):- When an iron object is left in damp air for a considerable time, it gets covered with a Red Brown flaky substance called Rust.

       The rusting of iron is a Redox reaction.

(2) Rancidity:→ The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called Rancidity (Vikritgandhita).

The development of rancidity of food can be prevented in the following ways;

(1) Rancidity can be prevented by adding anti-oxidants to foods containing fats and oils.

(2) Rancidity can be prevented by packing fat and oil containing foods  in nitrogen gas.

(3) Rancidity can be prevented by keeping foods in a refrigerator.

(4) Rancidity can be prevented by storing food in air tight containers.

(5) Rancidity can be prevented by storing foods away  from light. from light.

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