Answer:
A system is in equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction.
Step-by-step explanation:
In a system in equilibrium, the rupture and formation of new bonds from the formation and decomposition of substances must have the same reaction rate. Thanks to equal speeds we can say that a system in equilibrium is dynamic and in general every system tends to move spontaneously towards equilibrium. The environment never interferes.
For example.
N2 (g) + 3H2 (g) ---> 2NH3 (g) formation
2NH3 ----> N2 (g) + 3H2 (g) decomposition
N2 (g) + 3H2 (g) <------> 2NH3 (g) In equilibrium