Boiling water is a physical change. The chemical composition of water remains the same when it boils. The chemical formula for water is H\(_2\)O, and it remains the same whether the water is a liquid, gas, or solid. 

When sodium reacts with oxygen in the air, it breaks bonds in the sodium and oxygen molecules and forms new bonds in sodium oxide and sodium peroxide. This process is called oxidation, which is a chemical reaction. This reaction is similar to calcium metal dissolved in water.

Also, when kerosene is burnt, you can't recover it anymore, hence it is not easily reversible. It is a chemical change.