Final answer:
Silver tarnishing is a chemical change involving the reaction of silver with hydrogen sulfide to form silver sulfide. This reaction changes the chemical composition of the silver, resulting in a dark tarnish on its surface.
Step-by-step explanation:
Is silver tarnishing a chemical or physical change? Silver tarnishing is, in fact, a chemical change. This occurs when silver reacts with hydrogen sulfide (H₂S) gas in the air, a reaction that can be represented by a word equation: silver + hydrogen sulfide → silver sulfide + hydrogen. In this reaction, silver metal (Ag) combines with hydrogen sulfide gas to produce silver sulfide (Ag₂S) and hydrogen gas (H₂). Since tarnishing involves the formation of a new substance and a change in the chemical composition of the silver, it is not just a superficial or physical change, like melting or freezing.
The reaction that causes silver to darken is: 2Ag + H₂S → Ag₂S + H₂. Silver sulfide is the dark and streaky black compound that forms on the surface of silver items, such as platters, pitchers, and jewelry, when they tarnish. Removing tarnish often involves the use of polishes that not only remove the tarnish but also a small layer of the silver itself, further confirming that the process is chemical, not just physical.