Equilibrium constant (Kc); Le Chatelier’s Principle: Practice Questions

Which of the following is NOT a characteristic of a chemical system in a state of dynamic equilibrium?

Consider the following gaseous equilibrium system:
\( 2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)} \quad \Delta H = -197 \text{ kJ mol}^{-1} \)
Which of the following changes will result in an increase in the value of the equilibrium constant, \( K_c \), for the reaction?

A mixture of \( 1.0 \text{ mol} \) of \( \text{H}_2\text{(g)} \) and \( 2.0 \text{ mol} \) of \( \text{I}_2\text{(g)} \) is heated in a \( 1.0 \text{ dm}^3 \) sealed flask. When equilibrium is reached at \( 700 \text{ K} \), the concentration of \( \text{HI(g)} \) is found to be \( 1.6 \text{ mol dm}^{-3} \).
\( \text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons 2\text{HI(g)} \)
What is the value of the equilibrium constant, \( K_c \), for the reaction at \( 700 \text{ K} \)?

For the following reversible reaction at equilibrium in a closed container:
\( \text{N}_2\text{O}_4(\text{g}) \rightleftharpoons 2\text{NO}_2(\text{g}) \quad \Delta H = +57 \text{ kJ mol}^{-1} \)
Which of the following changes will shift the equilibrium position to the right?

Consider the following chemical equilibrium in an aqueous solution:
\( Cr_2O_7^{2-}(aq) + H_2O(l) \rightleftharpoons 2CrO_4^{2-}(aq) + 2H^+(aq) \)
The dichromate ion, \( Cr_2O_7^{2-}(aq) \), is orange and the chromate ion, \( CrO_4^{2-}(aq) \), is yellow. Which of the following statements is correct when a few drops of concentrated \( NaOH(aq) \) are added to the mixture at constant temperature?

Consider the following reversible reaction at equilibrium in a closed container:

\(2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)}\)

The forward reaction is an exothermic reaction. \( (\Delta H < 0) \)

(a) State and explain the effect on the position of equilibrium when the concentration of \(\text{O}_2\text{(g)}\) is increased at constant temperature and volume.

(b) State and explain the effect on the position of equilibrium when the temperature of the system is increased at constant volume.

At a certain high temperature, the following equilibrium is established in a 2.0 \(\text{dm}^3\) sealed container:

\(\text{PCl}_5\text{(g)} \rightleftharpoons \text{PCl}_3\text{(g)} + \text{Cl}_2\text{(g)}\)

Initially, 4.0 moles of \(\text{PCl}_5\) are placed in the container. At equilibrium, it is found that 1.0 mole of \(\text{Cl}_2\) has formed.

(a) Calculate the equilibrium constant, \(K_c\), for this reaction at this temperature. Show all your working.

(b) The forward reaction is endothermic. \( (\Delta H > 0) \) If the pressure of the system is increased by decreasing the volume at constant temperature, state and explain the effect on both the equilibrium position and the value of \(K_c\).