Final answer:
New substances form when heating different metals, highlighted by the chemical reaction of magnesium with oxygen which creates a bright white flame and magnesium oxide, and the physical change of a nichrome wire that glows when heated but returns to original state upon cooling.
Step-by-step explanation:
There is distinct evidence of new substances being formed when heating different metals. For instance, when magnesium wire is heated, it reacts with oxygen to create a bright white flame, and magnesium oxide (MgO), a crumbly white powder, is produced.
This reaction also releases heat, indicating a chemical change. In contrast, a nichrome wire, which is an alloy of nickel and chromium, when heated does not typically undergo a chemical change but rather a physical change as it gets hot and may glow due to resistance but returns to its original state upon cooling.
In the case of magnesium reacting with hydrochloric acid, the formation of hydrogen gas and the production of a clear solution containing magnesium chloride (MgCl2) are evidence of a chemical change. Similar evidence of a chemical change is observed when magnesium reacts with solid carbon dioxide, producing magnesium oxide and solid carbon.
Detecting a chemical change often involves observing the evolution of gas, change in color, heat or light production, or formation of new solid products. For example, a copper wire immersed in an aqueous solution of silver nitrate will gradually cause the solution to turn blue and the copper wire to become covered with a porous gray solid of silver, visibly indicating a chemical reaction.