This document discusses chemical reactions and equations. It defines chemical reactions as processes that form new substances with new properties. reactants are the initial substances, while products are the substances formed. Examples of chemical reactions in everyday life are provided. Characteristics of chemical reactions like gas evolution, precipitate formation, color change, and temperature change are described. Chemical equations are introduced as symbolic representations of reactions using symbols and formulae. The importance of balancing chemical equations so that mass is conserved is explained. Additional details that can be included in equations like physical states of substances and heat changes that occur are also outlined.

1. Chemical Reactions and Equations
 Introduction.
 Characteristics of Chemical Reactions.
 Chemical Equations. I
 Balancing of Chemical Equations
 Chemical Reactions - II
 Effects of Oxidation reactions in Everyday Life.-III
(Corrosion of Metals and Rancidity of Foods)
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Science
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2. Chemical Reactions and Equations
 Chemical reactions are the processes in which new
substances with new properties are formed.
 In a chemical reaction, the substances which react
together are called reactants whereas the substances
formed are called products.
 E.g. Magnesium + Oxygen Magnesium Oxide
 A large number of chemical reactions occuring in our
daily life are:- Souring of milk, Formation of curd
from milk, Cooking of food, Digestion of food in our
body, Respiration, Rusting etc.
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Science
Heat
(Air) (White powder)

3. Characteristics Of Chemical Reactions
 Evolution of a gas: -
 The chemical reaction between zinc and dilute sulphuric
acid is characterized by the evolution of Hydrogen gas.
 Formation of a precipitate :-
 The chemical reaction between sulphuric acid and barium
chloride is characterized by the formation a white
precipitate of barium sulphate.
 Change in colour:-
 The chemical reaction between citric acid and purple
coloured potassium permanganate solutions characterized
by a change in colour from purple to colourless.

4. Characteristics Of Chemical Reactions
 Change in Temperature:-
 The chemical reaction between quicklime and water to
form slaked lime is characterised by a change in
temperature (which is rise in temperature).
 Change in state :-
 The combustion reaction of candle wax is
characterized by a change in state from solid to liquid
and gas

5. Chemical Equations
 A chemical equation is the symbolic representation of a
chemical reaction in the form of symbols and formulae.
 Ex:- Magnesium + Oxygen Magnesium oxide
 This is known as the word equation.
 Mg + O2 MgO
 This Equation is known as Skeletal Equation (Skeletal
equation are those equation which shows the reactant
and product so formed without balancing them)
Reactants Product

6. Balanced Equations
 A balanced chemical equation occurs when the number of
the different atoms of elements in the reactants side is
equal to that of the products side.
 The chemical equation needs to be balanced so that it
follows the law of conservation of mass.
 Balancing of Chemical Equations :-
 The process of making the number of different types of
atom equal on both the sides of an equation is called
balancing of equation.
 Ex:- H2 + O2 H2O
No. Of Atoms In reactants ( LHS) In product ( RHS)
No. Of H atoms 2 2
No. Of O atom 2 1 X2 = 2

7. Balancing of Chemical Equations
 H2 + O2 2H2O
 2H2 + O2 2H2O
 To make Equations more informative :-
 By indicating the ‘physical states’ of the reactants and products.
 By indicating the ‘heat changes’ taking place in the reaction.
 By Indicating the ‘conditions’ in which reactions takes place.
No. Of Atoms In reactants ( LHS) In product ( RHS)
No. Of H atoms 2 X2= 4 4
No. Of O atom 2 2

8. Chemical Equations
 By indicating the ‘physical states’ of the reactants and
products :-
 The physical states of the reactants and products can be
shown by putting the state symbol like (s) for solid state, (l)
for liquid state, (aq) for aqueous solution & (g) for gaseous
state. Ex.
i) Zn(s) + H2SO4 (aq) ZnSO4(aq) + H2 (g)
ii) Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O (l)
 By indicating the ‘heat changes’ taking place in the
reaction :-
 There are two types of reactions on the basis of heat
changes involved Exothermic and Endothermic reactions.
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9.  Exothermic reactions :- Those reactions in which heat is
evolved are known as exothermic reactions.
 Ex. C (s) + O2 (g) CO2 (g) + Heat.
 Endothermic reactions :- Those reactions in which heat is
absorbed are known as endothermic reactions.
 Ex. CaCO3(s) + Heat CaO (s) + CO2 (g)
 By Indicating the ‘conditions’ in which reactions
takes place :-
 For the completion of reaction some time heat ( ),
Temperature (K or 0C ), Catalyst & pressure (atm.) or any
one can be required.
 Ex. 2KClO3(s) 2KCl(s) + 3O2 (g)
CO(g) + 2H2 (g) CH3OH (l)
MnO2
300atm,3000C
ZnO + CrO3

10. Dr. Mukesh Tiwary