Question

In a reversible reaction, chemical equilibrium is attained when ?
1. Rate of the forward reaction is greater than the rate of the reverse reaction.
2. Rate of the reverse reaction is greater than the rate of the forward reaction,
3. Concentration of the reactants reaches zero OR
4. Concentration of the products remains constant. i think its 4, right ?

Answer 1

In the context of the question, I would pick 4 but ONLY because 1,2, and 3 clearly are incorrect which means 4 is the only viable one to pick. However, I would quarrel with that answer, too, because, equilibrium is reached when the rate of the fwd rxn = rate of reverse reaction. Technically, then, the concn of of the products is changing (if only by a VERY SNALL amount). The point we try to get across to students is that equilibrium is a dynamic process; i.e., it is not a stationary state in which nothing is happening in the reaction. The reaction has not stopped. Reactants still are producing products and products still are forming reactants. The net amounts don't change.