Class 10 Science – Chapter 1
Chemical Reactions and Equations
1. Chemical Reaction
A chemical reaction is a process in which one or more substances change into new substances with different
properties.
Example: 2Mg + O■ → 2MgO
2. Signs of a Chemical Reaction
A chemical reaction may involve: change in colour, change in temperature, formation of a gas, formation of a
precipitate, or change in state.
3. Chemical Equation
A chemical equation represents a chemical reaction using symbols and formulae.
Example: Zn + H■SO■ → ZnSO■ + H■
Reactants: substances that take part in a reaction.
Products: new substances formed.
4. Balanced Chemical Equation
An equation is balanced when the number of atoms of each element is equal on both sides. This follows the
Law of Conservation of Mass.
Example: 2H■ + O■ → 2H■O
5. Types of Chemical Reactions
A. Combination: Two or more substances combine to form one product.
CaO + H■O → Ca(OH)■
B. Decomposition: One compound breaks into two or more simpler substances.
CaCO■ → CaO + CO■ (heat)
Types: thermal, electrolytic and photochemical.
2AgCl → 2Ag + Cl■ (sunlight)
C. Displacement: A more reactive element displaces a less reactive element.
Zn + CuSO■ → ZnSO■ + Cu
D. Double Displacement: Two compounds exchange ions.
Na■SO■ + BaCl■ → BaSO■ + 2NaCl
BaSO■ is a white precipitate.
6. Oxidation and Reduction
Oxidation: gain of oxygen, loss of hydrogen, or loss of electrons.
Reduction: loss of oxygen, gain of hydrogen, or gain of electrons.
Redox reaction: oxidation and reduction occur simultaneously.
CuO + H■ → Cu + H■O
7. Effects of Oxidation in Everyday Life
Chemical Reactions and Equations
1. Chemical Reaction
A chemical reaction is a process in which one or more substances change into new substances with different
properties.
Example: 2Mg + O■ → 2MgO
2. Signs of a Chemical Reaction
A chemical reaction may involve: change in colour, change in temperature, formation of a gas, formation of a
precipitate, or change in state.
3. Chemical Equation
A chemical equation represents a chemical reaction using symbols and formulae.
Example: Zn + H■SO■ → ZnSO■ + H■
Reactants: substances that take part in a reaction.
Products: new substances formed.
4. Balanced Chemical Equation
An equation is balanced when the number of atoms of each element is equal on both sides. This follows the
Law of Conservation of Mass.
Example: 2H■ + O■ → 2H■O
5. Types of Chemical Reactions
A. Combination: Two or more substances combine to form one product.
CaO + H■O → Ca(OH)■
B. Decomposition: One compound breaks into two or more simpler substances.
CaCO■ → CaO + CO■ (heat)
Types: thermal, electrolytic and photochemical.
2AgCl → 2Ag + Cl■ (sunlight)
C. Displacement: A more reactive element displaces a less reactive element.
Zn + CuSO■ → ZnSO■ + Cu
D. Double Displacement: Two compounds exchange ions.
Na■SO■ + BaCl■ → BaSO■ + 2NaCl
BaSO■ is a white precipitate.
6. Oxidation and Reduction
Oxidation: gain of oxygen, loss of hydrogen, or loss of electrons.
Reduction: loss of oxygen, gain of hydrogen, or gain of electrons.
Redox reaction: oxidation and reduction occur simultaneously.
CuO + H■ → Cu + H■O
7. Effects of Oxidation in Everyday Life
