Revision Notes for Class 10 Science
Chapter 1 – Chemical Reactions and Equations
Chemical Change: A change that results in the formation of one or more new compounds.
Chemical changes are also known as chemical reactions.
Observations in a Chemical Reaction
In a chemical reaction or chemical change, the following observations can be made,
• Formation of new substances.
• Change in mass.
• Changes in energy.
• Evolution of gas.
• Change in temperature.
• Permanent change in colour and/or state.
• Formation of a precipitate.
Examples :
A. Cooking of food
B. Rusting of iron
C. Heating of Lead nitrate
D. Souring of milk
E. Ripening of fruit.
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, Chemical Formulae - A substance's chemical formula is a symbolic representation of the
number of atoms present in a single molecule of that material.
a. One water molecule has the formula H2O . It demonstrates that one molecule of water is
made up of two hydrogen atoms and one oxygen atom.
b. One molecule of sulphuric acid has the formula H2SO4 . It illustrates that one molecule of
sulphuric acid has 2 hydrogen atoms, 1 sulphur atom, and 4 oxygen atoms.
Chemical Equations - The chemical equation of the reaction is the representation of a
chemical change in terms of symbols and formulae of the reactants and products.
Example:
KMnO4 + HCl → KCl + MnCl2 + H 2O + Cl2
Potassium Hydrochloric Potassium Manganese Water Chlorine
permanganate acid chloride chloride
Steps for writing Chemical Equation
A. Step I: Writing Skeletal Equation
A word-equation depicts the transformation of reactants into products by placing an arrow
between them ( → ). The arrow indicates the reaction's direction and might be read as "to
yield," "to form," or "to give."
The reactants are on the left (LHS) of the arrow, while the products are on the right (RHS).
A plus sign (+) links the different reactants and products together.
A balanced account of a chemical transaction is a complete chemical equation, which
symbolically depicts the reactants, products, and their physical states.
Class X Science www.vedantu.com 2
Chapter 1 – Chemical Reactions and Equations
Chemical Change: A change that results in the formation of one or more new compounds.
Chemical changes are also known as chemical reactions.
Observations in a Chemical Reaction
In a chemical reaction or chemical change, the following observations can be made,
• Formation of new substances.
• Change in mass.
• Changes in energy.
• Evolution of gas.
• Change in temperature.
• Permanent change in colour and/or state.
• Formation of a precipitate.
Examples :
A. Cooking of food
B. Rusting of iron
C. Heating of Lead nitrate
D. Souring of milk
E. Ripening of fruit.
Class X Science www.vedantu.com 1
, Chemical Formulae - A substance's chemical formula is a symbolic representation of the
number of atoms present in a single molecule of that material.
a. One water molecule has the formula H2O . It demonstrates that one molecule of water is
made up of two hydrogen atoms and one oxygen atom.
b. One molecule of sulphuric acid has the formula H2SO4 . It illustrates that one molecule of
sulphuric acid has 2 hydrogen atoms, 1 sulphur atom, and 4 oxygen atoms.
Chemical Equations - The chemical equation of the reaction is the representation of a
chemical change in terms of symbols and formulae of the reactants and products.
Example:
KMnO4 + HCl → KCl + MnCl2 + H 2O + Cl2
Potassium Hydrochloric Potassium Manganese Water Chlorine
permanganate acid chloride chloride
Steps for writing Chemical Equation
A. Step I: Writing Skeletal Equation
A word-equation depicts the transformation of reactants into products by placing an arrow
between them ( → ). The arrow indicates the reaction's direction and might be read as "to
yield," "to form," or "to give."
The reactants are on the left (LHS) of the arrow, while the products are on the right (RHS).
A plus sign (+) links the different reactants and products together.
A balanced account of a chemical transaction is a complete chemical equation, which
symbolically depicts the reactants, products, and their physical states.
Class X Science www.vedantu.com 2
