Chemical equilibria, Le Chatelier’s principle and Kc: Practice Questions

What is the effect of adding a catalyst to a reversible reaction that has already reached equilibrium at a constant temperature?

The Haber process involves the following equilibrium:
\( \text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \) \( \Delta H = -92 \text{ kJ mol}^{-1} \)
Which of the following changes would result in a decrease in the value of the equilibrium constant \( K_c \)?

A mixture of \( \text{SO}_2(g) \) and \( \text{O}_2(g) \) is allowed to reach equilibrium in a closed vessel of volume \( V \):
\( 2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g) \)
If the volume of the vessel is reduced to \( 0.5V \) at constant temperature, which statement is correct?

Which of the following conditions must be met for a chemical system to be at dynamic equilibrium?

In the homogeneous gas-phase reaction:
\( \text{A(g)} + \text{B(g)} \rightleftharpoons \text{C(g)} + \text{D(g)} \)
The initial concentrations of both \( \text{A} \) and \( \text{B} \) were \( 1.00 \text{ mol dm}^{-3} \). At equilibrium, the concentration of \( \text{C} \) was found to be \( 0.20 \text{ mol dm}^{-3} \). What is the value of \( K_c \) at this temperature?

Predict and explain the effect of adding a catalyst on the value of the equilibrium constant \(K_c\).

Deduce the units for the equilibrium constant \(K_c\) in the reaction:
\(2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)\).

A mixture containing 0.500 mol of \(\text{A}(g)\) and 0.500 mol of \(\text{B}(g)\) was allowed to reach equilibrium in a sealed container of volume \(V\) at a constant temperature. The equation for the reaction is:
\(\text{A}(g) + \text{B}(g) \rightleftharpoons \text{C}(g) + \text{D}(g)\)
At equilibrium, 0.400 mol of \(\text{C}(g)\) was found to be present.
(a) Write an expression for the equilibrium constant, \(K_c\).
(b) Calculate the value of \(K_c\) at this temperature.