Ch 6 explores the changes we see around us — reversible (can be undone) and irreversible (cannot be undone). Students learn to classify changes and understand why some changes can be reversed and others cannot.
Reversible: ice melting to water (can freeze back), stretching a rubber band, dissolving salt in water (evaporate to get salt back). Irreversible: burning paper, cooking food, curdling of milk — these cannot be undone.
Most materials expand on heating and contract on cooling. This is used in everyday life: gaps in railway tracks allow for expansion, tight metal lids can be loosened by heating.
Download: https://ncert.nic.in/textbook/pdf/fesc106.pdf | Complete book: https://ncert.nic.in/textbook/pdf/fesc1ps.zip
Melting of wax is reversible — when cooled, wax solidifies again. However, burning of wax is irreversible because it produces CO₂ and water vapour, and the original wax cannot be recovered.
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