Calcium oxide and carbon dioxide combine to form calcium carbonate in the reversible reaction:
CaO + CO2 ⇌ CaCO3
When the reaction is at dynamic equilibrium, which statement must be true?
Calcium carbonate and calcium oxide are formed at the same rate.
The forward and reverse reactions have stopped.
The concentration of calcium carbonate is increasing.
The reaction has run out of carbon dioxide or calcium oxide.
I don't like any of the choices but a is the best statement offered. I would have preferred that the statement read "At equilibrium the forward rate equals the reverse rate.
When the reaction is at dynamic equilibrium, the statement that must be true is: "Calcium carbonate and calcium oxide are formed at the same rate."
At dynamic equilibrium, the forward and reverse reactions are still occurring, but the rates of the forward and reverse reactions are equal. This means that the concentration of each compound involved in the reaction remains constant over time. In this case, the concentration of calcium carbonate is not increasing, and the reaction has not run out of carbon dioxide or calcium oxide as they are continuously being converted to calcium carbonate and vice versa.
When the reaction is at dynamic equilibrium, it means that the forward and reverse reactions are occurring at the same rate, and there is no net change in the concentration of any of the substances involved.
Therefore, the statement "Calcium carbonate and calcium oxide are formed at the same rate" must be true. At equilibrium, the rate of formation of calcium carbonate from calcium oxide and carbon dioxide is equal to the rate of decomposition of calcium carbonate into calcium oxide and carbon dioxide.
The statement "The forward and reverse reactions have stopped" is not true at equilibrium since the reactions are still occurring, just at the same rate.
The statement "The concentration of calcium carbonate is increasing" is not true at equilibrium since, at equilibrium, the concentrations of all substances remain constant.
The statement "The reaction has run out of carbon dioxide or calcium oxide" is not true at equilibrium because there is still carbon dioxide and calcium oxide present in the system. These substances may be used up or replenished, but their presence alone does not determine if the reaction is at equilibrium.