Here's why:

* Electrochemical Series: The electrochemical series ranks metals based on their tendency to lose electrons and form positive ions. Copper is higher on the electrochemical series than silver, meaning copper has a greater tendency to oxidize (lose electrons) and is therefore more reactive.

* Reactivity with Oxygen: Copper readily reacts with oxygen to form a green patina (copper oxide and copper carbonate). Silver, while it can tarnish (form silver sulfide), is less reactive with oxygen than copper.

* Reactivity with Acids: Copper reacts with dilute acids like nitric acid, but silver does not.

In summary, copper is more reactive than silver because it is more easily oxidized and readily forms compounds with other elements.