Carbon chemistry
Chemical change — রাসায়নিক পরিবর্তন
Quick answer
Bonds break and remake, giving brand-new substances — burning, rusting, souring, ripening; hard to undo, unlike physical changes.
Definition
In a chemical change, bonds between atoms break and new bonds form, so new substances appear with properties of their own. Signs include a lasting colour change, gas bubbles, a precipitate, light, or heat given out or taken in. Burning coal, rusting iron, souring milk, and ripening a mango are chemical changes, and they are hard to reverse: you cannot un-burn a match. The general name for any chemical change is a chemical reaction.
For example
Leave a wet iron khunti (spade) out in the monsoon air and brown rust slowly replaces the grey metal: iron and oxygen have chemically combined.