Physical change
Chemical change
Physiological change
Morphological change
Following points need special consideration:
- Physical change is reversible and temporary.
- The composition of the substance does not change during a physical change and hence, no new substance is formed.
- No loss or gain of energy takes place during a physical change. The energy needed to bring about a physical change is equal to energy that can reverse the change. For example, 2260 J of heat energy is needed to change 1 g of water at 100°C to 1g of steam at 100°C. The same amount of heat energy is given out when 1g of steam condenses to 1 g of water at 100°C.
- No change in mass occurs during a physical change. This is because the substance undergoing a change remains the same. No matter is added or removed.
Examples of physical change:
- Making of ice-cream
- Boiling water into steam.
- Crystallization of sugar from its solution,
- Sublimation of camphor.
- Bending of glass tube by heating.
- Melting of wax or an ice cube.
- Evaporation of water.
- Glowing of an electric bulb.
- Magnetising an iron bar by means of electricity.
- Dissolving sodium chloride or sugar in water.
- Clotting in blood.
- Ripening of fruit.
- Cutting wood.
- Crumpling paper.
- Formation of biogas.
- Burning of LPG gas.
Characteristics of a Chemical Change:
- Change in mass of the substance occurs during a chemical change. However, total mass of all the reactants and products remain unchanged.
- The composition of a substance changes during a chemical change.
- Either heat is absorbed or evolved during a chemical change i.e., chemical change is either exothermic or endothermic.The different atoms in a chemical compound are joined by attractive forces commonly called bonds. The formation or breaking of the bonds always requires exchange of energy.
- The chemical change is irreversible and permanent,It means that the change will not reverse by altering the experimental conditions.
Example: The sugar molecule which has decomposed on heating and form carbon and steam will not change to sugar on cooling.
Examples of Chemical changes
- Rusting of an iron knife.
- Burning of a candle.
- Digestion of food.
Obviously, the rust cannot be converted back into iron, the burnt products i.e., carbon dioxide and water, cannot form wax and the products formed on digestion cannot be brought back into the original food. - Burning of wood or charcoal.
- Decomposition of water into hydrogen and oxygen.
- Formation of water from hydrogen and oxygen.
- Curdling of milk.
- Baking of cake.
- Drying of paint.
- Mixing of acid.
- Boiling of an egg.
- Formation of methane in marshy areas.
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