What is the reaction for the dissolution of magnesium nitrate in water?
Many would classify the reaction depicted above as a physical reaction rather than a chemical one. And if you review the history of this thread in a few hours, you will probably see certain people making precisely that objection.
The reaction above is, nevertheless, a chemical reaction, in that we have taken solid magnesium nitrate, an ionic solid, and dissolved it in water to form aquated ions. We write
Chemical change is characterized by the formation of new substances and the making and breaking of strong chemical bonds. These are precisely what have happened in the chemical reaction depicted.