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Chapter – 6 Physical andChemical Changes Changes can beof two types, physical and chemical. 1. Physical changes are changes in the physical properties of substances. substances areformed in these changes.These changes maybe reversible. No new Example: crushing a can, glowing of an electric bulb, tearing of paper, mixing of sand and water. 2. Chemical Changes are changes in which the composition and chemical properties of the substance get changed. In chemical changes new substances are produced. This change is permanent andirreversible. Example: burning of a candle, formation of curdfrom milk, ripening of fruits. · Chemical Reactions in daily life: 1. Rusting of Iron: Rusting is the process in which ironturns into ironoxide. It happens when iron comes intocontact with waterand oxygen. Theprocess is a type of corrosion that occurs easily under natural conditions. Prevention of Rusting: (i) By Painting (ii) By Oiling andgreasing (iii) By Chromium plating (iv) By Galvanizing (v) By Alloying 2. Cooking of food: Cooking causes breakdown of complex molecules of carbohydrates, fats and proteins into smaller molecules. It is regarded as a decomposition reaction. Cooked food is easier to digest thanuncooked food.
3. Decayof Organic Substances: Microorganisms like fungi and bacteria produce enzymes which break down complex organic compounds intosmaller substances. It is also regarded as a decomposition reaction. Some substances canbe obtained inpure state fromtheir solutions bycrystallization.
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