Chemical Reactions and Equations

Chemical Reaction

Chemical reaction is a process in which new Substances with different properties are formed.Atoms of one element don't change into another element.Only Rearrangement of atoms takes place in a chemical reaction.

Characteristics of Chemical Reaction 

1.Change in Colour 

2.Change in state 

3.Change in Temperature

4.Evolution of Gas 

5.Formation of Precipitate 

Chemical Equation

The method of representing a chemical reaction with the help of symbols and formulae of the substances involved in it is known as Chemical Equation.

How to make the Chemical Equation more informative 

1.By indicating the "physical state" of the reactants:- There can be four physical states for the reactants and products of a chemical reaction i.e, Soli,Liquid,Gas,Aqueous Solution.

Solid is indicated by(s)

Liquid is indicated by (l)

Gaseous state is indicated by the symbol(g)

Aqueous solution is indicated by symbol(aq)

2.By indicating the "heat change" taking place in the reaction:-There are two types of reactants on the basis of heat changes involved 

i)Exothermic Reaction:- Those Reactions in which heat is evolved are known as Exothermic Reactions.It is denoted by "Heat+" or "+Heat Energy" on the product side of the equation.

Ex.Respiration,Thermite Reaction 

ii)Endothermic Reactions:- Those Reactions in which is is absorbed are known as Endothermic Reaction.It is indicated by writing in reactants side of equation.

Ex.Photosynthesis,Nitrogen monoxide formation

3.By indicating the "conditions" under which the recation takes place:-if heat is required for a reaction to take place them the heat sign delta ∆ is put over the arrow of the equation 

2KClO3(s)------>2KCl(s)+3O2(g)

If reaction takes place in the presence of catalyst,then the symbol or formula of catalyst is also written above or below the arrow Sign in the equation.

CO+2H2-------->CH3OH 

Types of Chemical Reaction 

There are 4 types of Chemical Reaction.

1.Combination Reaction:-

Those reactions in which two or more substances combines to form a single Substances are called Combination Reactions.

CaO+H2O----->Ca(OH)2

2.Decomposition Reaction:- 

Those reactions in which a compound spilts up into two or more simer substances are known as decomposition reaction.it is occurs by heat,Light,Electricity etc. Methods.

When decomposition reaction is carried out by heating then it is called thermal decomposition.

1.FeSO4(s)  ----heat---->Fe2O3(s)+SO(g)+SO3(g)

2.CaCO3(s)----Heat----> CaO+CO2 

The Decomposition reaction takes place by the action of electricity.it is called electrolysis.

1.2H2O -----Electricity----> 2H2 + O2 

2.2NaCl -----Electricity---->2Na+Cl2 

Black & White Photography 

1. 2AgCl-------Light----->2Ag+Cl2 

2. 2AgBr-------Light----->2Ag+Br2 

3.Displacement Reaction:- Displacement reactions are reactions in which one element takes the place of another element.

Examples:-

1.CuSO4+Zn-------> ZnSO4+Cu 

2. CuSO4 +Mg------> MgSO4 

3.Fe+2HCl--------> FeCl2+H2

Reactivity Series of Metal

K 

Na 

Ca 

Mg 

Al 

Zn 

Fe 

Sn 

Pb 

H

Cu 

Hg 

Ag 

Au 

P 

4.Double Displacement Reaction 

Those reactions in which two compounds react by exchange of ions to form two new compounds are called the double displacement reactions 

A double displacement reaction usually occurs in solution and one of the product being insoluble and precipitates out.

1.AgNO3+NaCl --------> AgCl+ NaNO3 

2.BaCl2+Na2SO4 ---------> BaSO4+2NaCl 

3.CuSO4+H2S ------> CuS +H2SO4 

Oxidation Reaction

1. The addition of oxygen to the substance is called oxidation 

2.The removal of hydrogen from a substance is also called oxidation.

i)2Ca+O2----->2CaO 

ii)CH3OH------->CH2O +H2 

iii)2Mg+O2------> 2MgO

Oxidising Agent 

1.This substance which give oxygen for oxidation is called oxidising agent 

2.This substance which remove hydrogen is also called oxidising agent.

Reduction

 1.The addition of hydrogen to a substance is called reduction 

2.The removal of oxygen to a substance is also called reduction.

i)ZnO+C-----> Zn+CO 

ii)H2+I2-------> 2HI

Reducing agent 

1.Those substance which gives hydrogen for reduction is called reducing agent 

2.Those substance which removes oxygen is also called Reducing Agent .

Redox reaction

Those reaction in which oxidation and reduction takes place simultaneously are referred as to redox reaction. Redox reaction also occurs when loss of electrons and gain of electrons occur in a substance simultaneously.

CuO+H2 -----> Cu+H2O 

Zn+CuSO4------> ZnSO4 +Cu

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