Final answer:
A chemical reaction can be identified by the formation of gas, melting of a substance, and dissolution or dissolving.
Step-by-step explanation:
One sign that a chemical reaction has occurred is the formation of a gas. When certain substances react with each other, they may produce gases as one of the products. For example, when vinegar (acetic acid) reacts with baking soda (sodium bicarbonate), carbon dioxide gas is formed, which can be observed as bubbles.
Another sign of a chemical reaction is the melting of a substance. Some reactions involve the absorption or release of energy, which can cause solids to melt or change their physical state.
Lastly, dissolution or dissolving is also a sign that a chemical reaction has taken place. When a substance dissolves in a solvent, its particles separate and mix with the solvent on a molecular level.
Learn more about Signs of a chemical reaction