Question

Raw rice boiled with water turns to cooked rice, why is it a chemical change?

Answer 1

As rice contains about 90% starch, rice-cooking is essentially the reaction of starch in water at elevated temperatures. Starch granules adsorb water and swell as the heating continues. When a certain temperature (call gelatinization temperature) is reached, the cell wall of the granule breaks and the starch turns viscous (gelatinized). That is essentially what happens during the cooking of rice.

There are two types of starch in rice, amylose and amylopectin. Long grain rice is rich in amylose, whereas short grain rice is rich in amylopectin. Cooked-rice properties vary, depending on the type of rice.