By : Aditya Kumar Pathak

• Chemical Equation (i)• Chemical Equation (ii)• Characteristics of Chemical Equations• Chemical equation: Reactant, Product & Chemical equation.• Types of Chemical equation• Word equations• Writing word Equations (i)• Writing word Equations (ii)• Writing symbol Equations• Unbalanced and Balanced Equations• Balancing of Chemical Equation (i)• Balancing of Chemical Equation (ii)• Exercise

A Chemical equation links together the substances which react (Reactants) with the new substances that are formed (Products).

H2 + O2 H2O

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Depict the kind of reactantsreactants and productsproducts and their relative amounts in a reaction.

4 Al(s) + 3 O2(g) 2 Al2O3(s)

The numbers in the front are called stoichiometric coefficientsstoichiometric coefficients.

The letters (s), (g), and (l) are the physical states of compounds.

reactantsreactants productproduct

aluminum oxide

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• The equation must represent known facts.

• The equation must contain the correct formulas for the reactants and products.

• The law of conservation of mass must be satisfied.

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• Reactants – the substances that exist before a chemical change (or reaction) takes place.

• Products – the new substance(s) that are formed during the chemical changes.

• CHEMICAL EQUATION indicates the reactants and products of a reaction.

REACTANTS PRODUCTS INDEX

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The Chemical equation are of two types. These are :

Word equations Symbol equation

• A WORD EQUATION describes chemical change using the names of the reactants and products.

Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water.

methane + oxygen

Reactant Product

CH4 O2 CO2 H2O+ + 22

carbon dioxide + water

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A word equation links together the names of the reactants with those of the products. For example, the word equation when magnesium ribbon burns in oxygen to form a white powder of magnesium oxide, may be written as follows :Magnesium + Oxygen Magnesium Oxide

(Reactants) (Product)

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In a word equation :The reactants are written on the left hand side with plus sign (+) between them. The products are written on the right hand side with plus sign (+) between them. An arrow ( ) separates the reactants from the products. The direction of the arrow head points towards the products

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A brief representation of a chemical reaction in terms of the substances involved.In a symbol equation, the symbol and formulae of the elements and compounds are written instead of their word names. For example, burning of magnesium in oxygen to form magnesium oxide may be written as follows :

Mg + O2 MgO INDEX

Cl

Cl

ClH

H

H

ClClCl

ClHH

H

H

H2 + Cl2 HCl H2 + Cl2 2 HCl

reactants products

H

Cl

reactants products

H

Cl

2

2

2 2

2 2

1

1

(unbalanced) (balanced)

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Balancing of chemical equation may be defined as :The process of making the number of different elements on both slides of the equation equal.

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The major steps involved in balancing a chemical equation are as follows :

Write the chemical equation in the form of a word equation. Keep the reactants on the left side and the products on right side. Separate them by an arrow head ( ) pointing from the reactants towards the products.

Convert the word equation into the symbol equation by writing the symbols and formulae of all the reactants and products.

Make the atoms of different elements on both sides of the equation equal by a suitable method. This is known as balancing of equation.

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I. Which of the following is a chemical equation(i) Mg - O MgO (ii) H2 + Cl2 HCl

(iii) 2H2 + O2

2H2O(iv) Mg + Cl MgO

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WRONG ANSWER

CORRECT ANSWER

II. Balance the following equations :Hydrogen + Chlorine

Hydrogen Chloride (i) H2

+ Cl2 HCl (ii)2H2

+ Cl24HCl (iii)H2 + Cl2 2HCl(iv) H + Cl 2HCl

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WRONG ANSWER

CORRECT ANSWER

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WRONG ANSWER

CORRECT ANSWER

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