Introduction to Equilibrium Practice Test

The reversible decomposition reaction $2\text{NOCl}(g) \rightleftharpoons 2\text{NO}(g)+\text{Cl}_2(g)$ is carried out in a sealed container at constant temperature. After some time, the measured concentrations remain constant.

Which statement correctly describes the system at equilibrium?

A student studies the reversible reaction $\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g)+\text{Cl}_2(g)$ in a closed container at constant temperature. After sufficient time, the measured concentrations of all gases remain constant.

Which statement best describes the meaning of equilibrium for this system?