Page 70 - Chemistry ICSE Class IX
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58 ICSE Chemistry – 9
Let us say it Again
Physical change. A change in which only the physical properties of the substance get changed, while its chemical
composition remains unchanged, is called a physical change.
A physical change is a temporary change.
A physical change is reversible in nature.
During a physical change, only the physical properties, such as physical form, colour and shape, undergo a change.
Chemical change. A change in which chemical composition and chemical properties of the reacting substances undergo
a change is called a chemical change.
Chemical change is a permanent change.
Chemical change is irreversible in nature.
Combination reaction. A reaction in which two or more substances combine together to form a new substance is called
a combination reaction.
Decomposition reaction. A reaction in which a substance is broken down into two or more simpler substances is called
a decomposition reaction.
Displacement reaction. A reaction in which one part of a molecule is replaced by another, is called a displacement
reaction.
Double-displacement reaction. A reaction in which two reacting molecules exchange their corresponding ions, is
called a double-displacement reaction.
Precipitation reaction. The reaction in which one of the products formed is an insoluble substance and is thrown out of
the solution as solid (called precipitate) is called precipitation reaction.
Exothermic reaction. The reaction in which heat is liberated (or given out) is called an exothermic reaction.
Endothermic reaction. The reaction in which heat is absorbed (or taken in) is called an endothermic reaction.
Redox reaction. A reaction in which oxidation and reduction reactions take place side-by-side is called a redox reaction.
Combustion. A chemical change/reaction in which heat and light, in the form of flame, are given out is called combustion. or
Combustion is the rapid oxidation or burning of any substance in which heat and light are given out.
Combustible and noncombustible substances. The substances which burn readily when ignited are called combustible
substances.
The substances which do not burn when ignited are called noncombustible substances.
Partial combustion. Burning of a combustible substance in the presence of a limited amount of air (or any other
supporter of combustion) is called partial (or incomplete) combustion.
