Answer:
Limescale formed on kettle walls
Explanation:
A chemical reaction is one which is associated with a chemical change. While the other two examples are mere change in physical state, the formation of limescale on kettle is a chemical change. It is called the furring of kettles.
These limescales are formed when Calcium bicarbonate decomposes into calcium carbonate. It is this calcium carbonate that causes the furring of kettles.
It is one of the consequence of using temporary hard water. Temporarily hard water contains soluble magnesium bicarbonate and calcium bicarbonate. Now the heating of this water causes the decomposition of the calcium bicarbonate into calcium carbonate which forms these scales on the body of the kettle.
Calcium bicarbonate decomposes into calcium carbonate according to the following equation;
CaH(CO3)2 (aq) ---------> CaCO3 (s) + H2O (l) + CO2 (g)
