Question
The table lists the initial concentrations of each substance in the system represented by the equation above at a given temperature. Which of the following best predicts what will occur as the system approaches equilibrium?
A The rate of the reverse reaction will be less than the rate of the forward reaction, and additional \(CH_3OH\)(g) will be consumed because \(K_c<Q_c\) .
B The rate of the reverse reaction will be greater than the rate of the forward reaction, and additional \(CH_3OH\)(g) will be consumed because \(K_c<Q_c\) .
C The rate of the forward reaction will be less than the rate of the reverse reaction and, additional \(CH_3OH\)(g) will be produced because \(K_c<Q_c\) .
D The rate of the forward reaction will be greater than the rate of the reverse reaction, and additional \(CH_3OH\)(g) will be produced because \(K_c<Q_c\).
▶️Answer/Explanation
Ans:B
\(Q_c=\frac{[CH_3OH]}{[CO][H_2]^2}=\frac{(0.10)}{(0.10)(0.10)^2}=100\) , and when \(K_c<Q_c\), the rate of the reverse reaction will be greater than the rate of the forward reaction, resulting in the net consumption of CH3OH(g) until equilibrium is reached.
Question
The chemical reaction shown above took place inside a rigid container at constant temperature. The table provides the concentrations of reactants and products at some point during the reaction. Based on this information, which of the following explains whether or not the reaction has reached equilibrium, and why?
A The reaction is not at equilibrium because \(Q_c>K_c\) ; the forward reaction is favored in order to form more XY .
B The reaction is not at equilibrium because \(Q_c<K_c\) ; the reverse reaction is favored in order to form more \(X_2\) and \(Y_2\) .
C The reaction is not at equilibrium because \(Q_c<K_c\) ; the forward reaction is favored in order to form more XY .
D The reaction is at equilibrium because \(Q_c=K_c\) ; the amount of \(X_2\), \(Y_2\) and XY will remain the constant.
▶️Answer/Explanation
Ans:C
The expressions for \(Q_c\) and \(K_c\) are similar: \(Q_c=\frac{[XY]^2}{[X_2][Y_2]}=\frac{(0.20)^2}{(0.10)(0.30)}\)≈1.3. When \(Q_c<K_c\), the reaction is not at equilibrium and will favor the forward reaction to form additional XY.
Question
\(COCl_2(g)\)⇄\(CO(g)+Cl_2(g)\)
At a given temperature, the system represented by the chemical equation above is at equilibrium inside a rigid container. Which of the following explains how the system will restore equilibrium, based on the correct relationship between Q and K, after a certain amount of \(Cl_2\)(g) is added?
A Since \(Q=\frac{[Cl2][CO]}{[COCl_2]}\) , \(Q>K\) when \(Cl_2\)(g) is added to the system; the system will restore equilibrium by producing more \(COCl_2(g)\) .
B Since \(Q=\frac{[Cl2][CO]}{[COCl_2]}\) , \(Q<K\) when \(Cl_2\)(g) is added to the system; the system will restore equilibrium by producing more \(CO(g)\) .
C Since \(Q=\frac{[COCl_2]}{[Cl2][CO]}\) , \(Q>K\) when \(Cl_2\)(g) is added to the system; the system will restore equilibrium by producing more \(COCl_2(g)\) .
D Since \(Q=\frac{[COCl_2]}{[Cl2][CO]}\) , \(Q>K\) when \(Cl_2\)(g) is added to the system; the system will restore equilibrium by producing more \(CO(g)\) .
▶️Answer/Explanation
Ans:A
Based on the mathematical expression for Q , \(Q=\frac{[Cl2][CO]}{[COCl_2]}\), the addition of \(Cl_2\) increases the numerator in this ratio, which increases the magnitude of Q overall. When \(Q>K\), the system will restore equilibrium by increasing the rate of the reverse reaction in the equilibrium and more \(COCl_2\) will be produced.
Question
\(PC1_3(g) + Cl_2(g) \rightleftharpoons PCl_{5}(g)\) \( K_{c} 6.5\)
36. At a certain point in time, a 1.00 L rigid reaction vessel contains 1.5 mol of PCl,(g), 1.0 mol of \(Cl_2\)(g), and 2.5 mol of\( PCl_5\)(g). Which of the following describes how the measured pressure in the reaction vessel will change and why it will change that way as the reaction system approaches equilibrium at constant temperature?
(A) The pressure will increase because \(Q< K_c\)
(B) The pressure will increase because \(Q > K_c\)
(C) The pressure will decrease because \(Q< K_c\)
(D) The pressure will decrease because \(Q > K_c\)
▶️Answer/Explanation
Ans:C
Question
\(3O_{2}(g)\rightleftharpoons 2O_{3}(g) \) \(K_{c}=1.8\times 10^{-56}\)at 570k
For the system represented above, [\(O_{2}\)] and \([O_{3}]\) initially are 0.150 mol/L and 2.5 mol/L respectively. Which of the following best predicts what will occur as the system approaches equilibrium at 570 K?
(A) The amount of\( O_{3}\)(g) will increase, because Q<K
(B) The amount of \(O_{3}\)(g) will decrease, because Q<K
(C) The amount of \(O_{3}\)(g) will increase, because Q> K
(D) The amount of \(O_{3}\)(g) will decrease, because Q>K
▶️Answer/Explanation
Ans:C