This document provides key notes on chemical reactions and equations from a 10th grade chemistry textbook. It defines chemical reactions as processes that form new substances with different properties than the reactants. Chemical equations are used to represent chemical reactions symbolically and show the physical states of reactants and products. For equations to be balanced, the number of atoms of each element must be the same on both sides of the reaction. The document also describes several types of chemical reactions including combination reactions, decomposition reactions, displacement reactions, and double displacement reactions. Thermal, electrolytic, and photolytic decomposition reactions are given as examples.

1. GRADE: 10 CHEMISTRY‐KEY NOTES
CHAPTER‐1.CHEMICAL REACTIONS AND EQUATIONS
Chemical reactions are the processes in which new substances with properties different
from those of
the reactants are formed.
e.g. – Food gets digested in our body
Rusting of iron.
It involves breaking of bonds in the atoms of reacting substances and formation of new
bonds
between the atoms of the products.
The substances which take part in a chemical reaction are called reactants. The substances
which are
formed as a result of a chemical change during a chemical reaction is called products.
The chemical equation is a statement that describes a chemical change in terms of
symbols and
formulae. Physical state of the reactant and products are mentioned to make chemical reaction
more
informative. e.g. we use (g) for gas, (l) for liquid, (s) for solid and (aq) for aqueous.
Balancing Equation: We balance the chemical equation so that no. of atoms of each
element involved
in the reaction remains same at the reactant and product side.
e.g. Fe + H2O → Fe2O3 + H2
Can be written as
3 Fe(s) + 4H2O(g) → Fe2O3 (s) +4H2 (g)
The law of conservation of mass states that the total mass of the element present in the
product of a
chemical reaction is equal to the total mass of the elements present in the reactants.
The reactions in which two or more substances combine to form a single substance are
called
combination reactions.
eg CaO(s) + H2O(l) → Ca(OH)2 (aq)
Calciumoxide (Quick lime) Water Calciumhydroxide (slaked lime)
The reactions in which a compound splits up into two or more simpler substances are called
decomposition reactions. Decomposition reactions are opposite to combination reactions.
De
composition reactions can be of three types;
(a) Thermal decomposition:‐ when a decomposition reaction is carried out by heat
E.g. CaCO3 (s) Heat CaO (s) + CO2
(Lime stone) (Quick lime)
(b)Electrolytic decomposition:‐When a decomposition reaction is carried out by electric
current
e.g. H2O (l) electric 2H2 (g) + O2(g)
current

2. (c)Photolytic decomposition:‐ When a decomposition reaction is carried out by light
2AgCl(s) Sunlight 2Ag(s) + Cl2(g)
Silver bromide behaves similarly
2AgBr(s) Sunlight 2Ag(s) + Br2 (g)
The above two reactions are used in black and white photography.
The reactions in which heat is given out along with the products are called
exothermic reactions.
The reactions in which heat energy is absorbed are called endothermic reactions.
Displacement Reaction : The chemical reaction in which an element displaces another
element from
its solution. In general, a more reactive metal displaces a less reactive metal. This type of
chemical
reaction is based on the reactivity series.
Fe(s) + CuSO4(aq) → FeSO4 + Cu(s)
Copper sulphate Ironsulphate
Double Displacement Reaction : The reaction in which two different atoms or group of
atoms are
mutually exchanged
eg. Na2 SO4 (aq)+ BaCl2(aq)→ BaSO4(s) + 2NaCl (aq)
Sodium Sulphate Barium Chloride Barium Sulphate Sodium Chloride
A white substance is formed due to above reaction. The insoluble substance is called precipitate
Done by mukul