A student is told that a reversible reaction can only reach a true equilibrium under certain conditions. Which condition must be met for a reversible reacti...
Question 1 Report
A student is told that a reversible reaction can only reach a true equilibrium under certain conditions. Which condition must be met for a reversible reaction to reach equilibrium?
Answer Details
Equilibrium means the forward and backward reactions are proceeding at equal rates, so the amounts of every substance stay constant. That balance can only be set up if nothing can leave or enter, which is why the system must be closed.
If the vessel is open, any gaseous product escapes. Its concentration never builds up, the backward reaction can never match the forward one, and by Le Chatelier's principle the equilibrium keeps shifting forwards until the reactants are used up. This is exactly why heating limestone in an open kiln decomposes it completely, whereas in a sealed vessel it reaches equilibrium.
A catalyst only changes how fast equilibrium is reached, and there is no requirement for equal masses: the equilibrium amounts depend on the reaction and the conditions.
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