When the system A + B C + D is at equilibrium,
a. the forward reaction has stopped.
b. the reverse reaction has stopped.
c. both the forward and the reverse reactions have stopped.
d. neither the forward nor the reverse reaction has stopped.
e. the sum of the concentrations of A and B must equal the sum of the concentrations of C
and D.
Answer: d. neither the forward nor the reverse reaction has stopped.