Equilibrium is the condition whereby there are no changes with time nor any tendency to change with time.
By no tendency to change with time, we mean that all driving forces in the system are balanced.
This means all driving forces are balanced.
Distinguish between equilibrium and steady state
Explain why only closed systems may be in equilibrium.
Give examples of systems at steady state but not in equilibrium.
Note that this necessitates a closed system because an open system -- where material flows across the boundaries -- would require that there is a tendency of the material to change position with time (also there is an out of balance driving force that creates the movement).
A stable equilibrium is one that a system will return to when perturbed.