10 Sc Chem Chemical Reaction

Chemical Reactions and Equations There are two types of reactions (1) CHEMICAL REACTION (2) PHYSICAL REACTION CHEMICAL REACTION : In a reaction when the original state of the particle changes and it cannot be reversed by simple physical means, this type of reaction is known as chemical reaction. Example :- Fermentation of grapes, burning of wood etc. In this reaction we have seen that after burning of wood, coal is formed and we cannot make wood from coal. PHYSICAL REACTION : In a reaction when original state of the particle can be recovered by any means then this type of reaction is known as physical reaction. Example :- Evaporation of water is the example of physical reaction because we can turn vapour into water again WRITING A CHEMICAL RECTION When we are going to write a chemical equation then there will be reactant and product. Left hand side of the equation is called reactant and the right hand side of the equation is called product. 2H2+ O2 = 2H20 Reactant Product Balanced Chemical Equations According to the Law of conservation of energy we know that energy can neither be created nor destroyed. So while writing a chemical equations we should keep in mind that number of atoms in L.H.S and R.H.S of an equation should me balanced. TYPES OF CHEMICAL REACTION COMBINATION REACTION :-In a combination reaction two or more substances combine to form a new single substance. Example:

CaO + H2O = Ca(OH)2 Quick Lime

Slaked Lime

2H2 + O2 = 2H2O

Hydrogen

Oxygen

Water

DECOMPOSITION REACTION :-- Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances. Example: 2Fe SO4 = Fe2O3 + SO2 + SO3 Ferrous Sulphate Ferric Oxide

DISPALCEMENT REACTION :- When an element displaces another element from its compound, a displacement reaction occurs. Example : Fe + CuSO4 = FeSO4 + Cu Copper Sulphate

Iron Sulphate

DOUBLE DISPLACEMENT REACTION :-- Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions. Example: Na2SO4 + BaCl2 = BaSO4 + 2NaCl Sodium Sulphate + Barium Chloride = Barium Sulphate + Sodium Chloride

EXOTHERMIC REACTION :-- Reaction in which heat generated is called exothermic reaction. ENDOTHERMIC REACTION :-- Reaction in which energy is absorbed is known as endothermic reaction. Oxidation and Reduction OXIDATION :-- Oxidation is the gain of oxygen or loss of hydrogen. If a substance gains oxygen during a reaction, it is said to be oxidized. REDUCTION :-- Reduction is the loss of oxygen or gain of hydrogen. If a substance loses oxygen during a reaction it is said to be reduced. Example: 2Cu + O2 = 2CuO Copper is getting oxidised

CuO + H = Cu + H2O

2 Copper Oxide is reduced

Corrosion We must have observed that iron particles are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. Corrosion is harmful for many things, like car body, electric poles,etc. To prevent corrosion most of the things made of metal are given a thick coat of paint. Example :- The black coating on silver and the green coating on copper are common examples of corrosion.