Video Transcript
Calcium oxide can be made on a
large scale by heating calcium carbonate in a furnace. The furnace uses a lot of energy
when heating up to the required temperature and additional calcium carbonate is
frequently added to keep the reaction running, as shown. CaCO3 solid is in equilibrium with
CaO solid plus CO2 gas. Why does this reaction not reach
equilibrium? (A) The furnace is too hot. (B) The rate of reaction is too
slow. (C) The reaction is
irreversible. (D) The amount of reactants and
products remains constant. (E) The furnace is not a closed
system.
In order to understand why this
reaction does not reach equilibrium, we first need to understand what equilibrium
is. A dynamic equilibrium is an
equilibrium between forward and reverse reactions where both reactions occur at the
same nonzero rate. We can see that the provided
reaction equation is an equilibrium equation where both the forward and reverse
reactions can occur. So, the reaction could reach
equilibrium if the rate of the forward and reverse reactions occur at the same
rate.
However, we are told in the
question that when this reaction is carried out on a large scale in a furnace, it
does not reach equilibrium. If we look at the reaction
equation, we can see that two of the species are solids and one is a gas. The furnace where this reaction is
carried out is an open system. This means that matter can be
exchanged with the surroundings. So, when the calcium carbonate is
heated in the furnace, the carbon dioxide gas can escape. If the carbon dioxide is no longer
present, then the furnace no longer has the compounds necessary for the reverse
reaction to proceed. Without the reverse reaction,
equilibrium cannot be established.
So, if an equilibrium reaction
involves gases, dynamic equilibrium can only be established in a closed system, a
system that does not exchange matter with its surroundings. Therefore, this reaction does not
reach equilibrium because the furnace is not a closed system: answer choice (E).