Chemical reaction — রাসায়নিক বিক্রিয়া
A chemical reaction is a process in which bonds break and new ones form, turning starting substances into different new substances.
Definition
In a chemical reaction the atoms of the reactants rearrange: old bonds break, new bonds form, and substances with new properties appear — new colour, smell, taste or state. The tell-tale signs include a gas bubbling out, a precipitate settling, a colour change, or heat given off or taken in. Atoms are never created or destroyed in an ordinary reaction, so the total mass of the products always equals the total mass of the reactants — Lavoisier's law of conservation of mass.
For example
Leave a cut apple on the table and oxygen slowly turns it brown; slice an onion and a newly made substance reaches your eyes and makes them water — both quiet chemical reactions.