Baking soda, also known as sodium bicarbonate, is highly soluble in water. This means that it can easily be dissolved in water but can also be fully recovered when the water is evaporated.
Dissolving baking soda in water is considered a physical change, as it does not alter the chemical properties of either the baking soda or the water. Despite dissolving, the baking soda still remains chemically pure as NaHCO3 throughout the process.
On the other hand, when baking soda is heated, it undergoes a chemical change that breaks the molecules apart to produce sodium carbonate, water and carbon dioxide.