Why can equilibrium not be reached in reversible enzymatic rxn?

Enzymatic reactions are usually reversible reactions, that is, the reaction can go forward and backward. In this kind of situation, the reactants and the products are not fully consumed and both the forward and the backward reactions are occurring simultaneously, thus the reaction can never reach equlibrum.

Yes it would be a physical change.

What are the options? physical property can be color, smell, opacity, viscosity, density, infra red spectrum, melting and boiling points, attraction and repulson to magnets, etc.