Defined of chem term

Qc refers to a quotient formed by product concentrations/reactant concentrations. the system refers to may be not at equilibrium.

But Kc is an equilibrium constant. It states the quotient's value when the system is at equilibrium at a particular temperature.

That means Qc = Kc, the system is at equilibrium.

If Qc<Kc, the system is not at equilibrium and forward reaction rate > reverse reaction rate. after a period of time,
forward reaction rate = reverse reaction rate and equilibrium will be established.

If Qc>Kc, the system is not at equilibrium and forward reaction rate < reverse reaction rate. after a period of time,
forward reaction rate = reverse reaction rate and equilibrium will be established.