A system can be said to be in chemical equilibrium when (Choose all correct answers -- there may be more than one!)

In chemical equilibrium, a system meets specific conditions that indicate a balanced state in the chemical reactions occurring within it. The correct conditions are:

1. The rates of the forward and reverse reactions are equal. This means that the rate at which reactants are converted to products is the same as the rate at which products are converted back to reactants.

2. The concentrations of reactants and products remain constant over time. Although the reactions continue to occur, there is no net change in the concentration of the substances involved.

3. The system is closed, meaning no matter or energy is exchanged with the surrounding environment, allowing the equilibrium to be maintained.

4. The observable properties of the system, such as color or pressure, do not change, indicating that the system has reached a balanced state.

In summary, for a system to be in chemical equilibrium, it is crucial that the rates of reactions are equal, concentrations remain constant, the system is closed, and observable properties do not change.