Equilibrium (College Board AP® Chemistry): Flashcards
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Define dynamic equilibrium.
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Define dynamic equilibrium.
A state in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of all species remain constant over time.
Why is chemical equilibrium described as "dynamic" rather than "static"?
At equilibrium, the forward reaction and reverse reaction continue to occur at the same constant rate — molecules are still reacting in both directions. The system appears unchanged only because the rates are equal, not because all reaction has stopped.
True or False?
Irreversible reactions are represented using a double half-arrow symbol (⇌).
False.
Irreversible reactions are represented with a single forward arrow (→). The double half-arrow (⇌) denotes a reversible reaction.
Define irreversible reaction.
A reaction that proceeds in one direction only, stopping when at least one reactant is completely consumed. It is denoted by a forward arrow (→).
How can equilibrium be identified from a concentration–time or partial pressure–time graph?
Equilibrium is reached at the point where the concentrations or partial pressures of all species stop changing and remain constant. On the graph this appears as each curve becoming horizontal and flat.
True or False?
At equilibrium, the concentration of reactants must equal the concentration of products.
False.
At equilibrium the concentrations of reactants and products are constant, but they are not necessarily equal. The equilibrium constant K determines the ratio of products to reactants.
At dynamic equilibrium, the rate of the forward reaction is .......... to the rate of the reverse reaction, and the concentrations of all species remain .......... .
At dynamic equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction, and the concentrations of all species remain constant.
Define reversible reaction.
A reaction that can proceed in both the forward and reverse directions simultaneously, denoted by the double half-arrow symbol (⇌). Products can react to reform reactants.
Why does a reversible reaction reach equilibrium over time, rather than continuing to convert all reactants to products?
As the forward reaction consumes reactants, its rate decreases while rising product concentrations increase the rate of the reverse reaction. Equilibrium is reached when both rates become equal, so there is no net change in composition.
True or False?
In a reversible reaction, only the forward reaction occurs until equilibrium is established.
False.
Both the forward and reverse reactions occur simultaneously from the start. Equilibrium is reached when the two rates become equal, not when one reaction begins.
How is the overall direction of a reversible reaction determined before equilibrium is reached?
By comparing the rates of the forward reaction and reverse reaction: if the forward rate is greater there is net conversion of reactants to products, and if the reverse rate is greater there is net conversion of products to reactants. The overall direction continues until both rates become equal at equilibrium.
True or False?
A reaction involving a gas in an open container can reach a reversible equilibrium.
False.
Reversible equilibrium for a gas-phase reaction requires a closed system. In an open container, gaseous products escape, so the reverse reaction cannot reach the same rate as the forward reaction.
A reversible reaction proceeds in an overall direction until the rate of the forward reaction is .......... to the rate of the reverse reaction, at which point .......... is established.
A reversible reaction proceeds in an overall direction until the rate of the forward reaction is equal to the rate of the reverse reaction, at which point equilibrium is established.
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