Question

why can not reach react to its to own salt

Answer 1

Sometimes it does! … but it just doesn’t look like it.

It’s all about equilibrium.

Let’s use your example. However, let’s say we have copper metal in an aqueous solution of copper (II) sulfate.

You have a big chunk of copper atoms all stuck (metallic bonding!) together. In the solution, you have mostly water; copper+2 ions; and sulfate-2 ions. When a copper ion brushes up against the metallic copper, it might happen to hijack two electrons from the highly conductive copper metal and bond with it. However, now the chunk of copper has an overall +2 charge, and this isn’t stable. Along comes a sulfate-2 ion and bumps up against the surface of the copper metal. If electronic conditions are right, the sulfate ion pulls a copper ion off the surface into solution, like a really attractive dancer pulling a wallflower away from their friends and onto the dance floor.

So, the copper ion that used to be in solution is now metallic, no charge, and the copper atom is now an ion. The reaction is happening, but the opposite reaction is also happening. That’s equilibrium.