16. When a reaction is at equilibrium

a. The forward reaction rate is equal to zero

b. The forward reaction rate is slower than the reverse reaction rate

C. The reverse reaction rate is equal to zero

d. The forward reaction rate is equal to the reverse reaction rate

The forward reaction rate is equal to the reverse reaction rate

Explanation:

In many cases, a lot of people might think that equilibrium is a state when a reaction stops. This is not the case, however. Notice that equilibrium reactions are represented by double arrows indicating that two reactions take place simultaneously: both a forward and a reverse reaction.

When equilibrium is reached, the rate of a forward reaction becomes equal to the rate of a reverse reaction. The two reactions don't stop and still take place, just at equal rates. This is the reason why the concentrations of reactants and products are kept constant at equilibrium: the rates of the two reactions are balanced.