why should you stop the reflux when the nitrogen dioxide (red gas) is no longer evolving? What is the concept of equilibrium?

Answer 1

You need to tell us specifically what experiment you are talking about and the equilibrium you have.

Answer 2

she is talking about conversion of benzaldehyde to benzilic acid. in a second part of the experiment where you convert benzoin to benzil, during the reflux, red gas is evolving

Answer 3

Yea, I'm talking about the experiment Nino said.