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Transformation of substances

  • Changes can broadly be classified into two types − physical and chemical. 
    • The characteristics of physical and chemical changes

Physical Change

Chemical Change

1. The chemical composition of a substance does not change.

1. The chemical composition of a substance changes.

2. Most changes are reversible.

2. Most changes are irreversible.

3. No new substances are formed. For example,

Ice → Water → Steam

3. New substances are formed. For example,

Paper → Ashes

  • Burning a candle is a combination of physical and chemical change.



Types of reactions

Combination reaction
Two or more reactants combine to form one single product.


CaOsCalcium oxide(Quick lime)+H2OlWaterCaOH2aqCalcium hydroxide(Slaked lime)CsCarbon+O2gOxygenCO2gCarbon dioxide2H2gHydrogen+O2gOxygen2H2OlWater

• Exothermic reaction – Heat gets released in the reaction. Most combination reactions are exothermic. For example,

CaOsCalcium oxide(Quick lime)+H2OlWaterCaOH2aqCalcium hydroxide(Slaked lime)

• Endothermic reaction Heat is absorbed in the reaction. Very few …

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