How far? the extent of chemical change: notes and practice questions

The synthesis of ammonia and the formation of nitrogen monoxide are two important industrial processes. The equilibrium constants for these reactions at 500 K are given below.

Reaction 1: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ $K_c = 6.0 \times 10^{-2}$

Reaction 2: $N_2(g) + O_2(g) \rightleftharpoons 2NO(g)$ $K_c = 1.7 \times 10^{-13}$

Which statement is correct at 500 K?

A. Reaction 1 goes almost to completion.

B. Reaction 2 has a greater yield of products than Reaction 1.

C. Both reactions favour the reactants.

D. The rate of Reaction 1 is greater than the rate of Reaction 2.

The reversible reaction between dinitrogen tetroxide and nitrogen dioxide is at equilibrium in a sealed container at a constant temperature.

$N_2O_4(g) \rightleftharpoons 2NO_2(g)$

The volume of the container is decreased. Which statement describes the effect on the composition of the mixture when a new equilibrium is established?

A. The amount of $N_2O_4(g)$ will have decreased.

B. The amount of $NO_2(g)$ will have increased.

C. The amounts of both gases will remain unchanged.

D. The amount of $N_2O_4(g)$ will have increased.

Consider the following system at equilibrium:

$N_2O_4(g) \rightleftharpoons 2NO_2(g)$

$\Delta H^\ominus = +58$ kJ mol⁻¹

Which row correctly describes the initial effect of a change in pressure on the equilibrium position and the relationship between the reaction quotient, Q, and the equilibrium constant, K?

A chemical engineer is investigating several gas-phase reactions for a new industrial process. For which of the following reactions will an increase in pressure have no effect on the position of the equilibrium?

A. $CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$

B. $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$

C. $N_2O_4(g) \rightleftharpoons 2NO_2(g)$

D. $CO(g) + H_2O(g) \rightleftharpoons CO_2(g) + H_2(g)$

Which statement about this equilibrium reaction is correct?

$[Cu(H_2O)_6]^{2+}(aq) + 4Cl^{-}(aq) \rightleftharpoons [CuCl_4]^{2-}(aq) + 6H_2O(l)$

A. Adding water to the reaction mixture shifts the position of equilibrium to the right.

B. Adding a source of chloride ions, such as NaCl(s), shifts the position of equilibrium to the left.

C. Removing chloride ions by adding $AgNO_3(aq)$ shifts the position of equilibrium to the left.

D. Removing water from the reaction mixture has no effect on the position of equilibrium.

Vanadium(V) oxide, $V_2O_5$, is used as a catalyst in the Contact process for the synthesis of sulfur trioxide: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$. What is the effect of adding this catalyst on the value of the equilibrium constant, $K_c$?

A. It increases.

B. It decreases.

C. It remains unchanged.

D. It depends on the initial concentration of $SO_2$.

The synthesis of methanol is a reversible reaction, as shown by the equation below.

$CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g) \quad \Delta H^{\ominus} = -91\text{ kJ mol}^{-1}$

Which set of conditions would produce the highest yield of methanol at equilibrium?

Pressure Temperature
A. high high
B. high low
C. low high
D. low low

Dinitrogen tetroxide, a colourless gas, is in equilibrium with nitrogen dioxide, a brown gas, in a sealed container at a constant temperature. The equation for this reversible reaction is:

$N_2O_4(g) \rightleftharpoons 2NO_2(g)$

If the pressure in the container is increased by decreasing the volume, what is the effect on the value of the equilibrium constant, $K_c$?

A. It will increase.

B. It will decrease.

C. It will stay the same.

D. It cannot be determined without the value of $\Delta H$.

A sealed flask contains liquid bromine, Br₂(l), in equilibrium with its vapour, Br₂(g), at a constant temperature. A small quantity of bromine containing the radioactive isotope ⁸²Br is injected into the liquid phase.

Which statement describes the system after a period of time?

A. The total pressure inside the flask will increase.

B. The radioactive ⁸²Br atoms will be found only in the liquid phase.

C. The total amount of liquid bromine will decrease.

D. The bromine vapour will become radioactive.

The Contact process is used for the industrial production of sulfuric acid. One key step is the reversible reaction between sulfur dioxide and oxygen, catalysed by vanadium(V) oxide:

$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$

What is the effect of the vanadium(V) oxide catalyst on this reaction?

A. It increases the equilibrium yield of sulfur trioxide.

B. It increases the value of the equilibrium constant, $K_c$.

C. It increases the rate at which equilibrium is attained.

D. It decreases the enthalpy change, $\Delta H$, for the forward reaction.

A substance is added to a reversible reaction which is observed to increase the rate at which equilibrium is attained. Which statement correctly describes the function of this substance?

A. It increases the average kinetic energy of the reactant particles.

B. It increases the value of the equilibrium constant, $K_c$.

C. It provides an alternative reaction pathway with a lower activation energy.

D. It is permanently consumed during the reaction.

The following equilibrium is established in a closed container at a specific temperature.

$2NO_2(g) \rightleftharpoons N_2O_4(g) \quad K_c = 0.25$

What is the value of the equilibrium constant, $K_c$, for the reverse reaction at the same temperature?

A. $0.25$

B. $0.0625$

C. $2.0$

D. $4.0$

Methanol is produced industrially by the reaction of carbon monoxide with hydrogen. What is the effect of increasing the volume of the reaction vessel on the equilibrium? All other conditions remain unchanged.

$CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$

A. shifts right, no change

B. shifts left, no change

C. shifts right, decreases

D. shifts left, decreases

A saturated solution of lead(II) chloride, $PbCl_2$, is in contact with solid $PbCl_2$ in a sealed container at constant temperature. A small amount of solid $PbCl_2$ containing the radioactive isotope chlorine-36 ($^{36}Cl$) is added. The system is allowed to re-establish equilibrium.

$PbCl_2(s) \rightleftharpoons Pb^{2+}(aq) + 2Cl^-(aq)$

Which observation would confirm that the equilibrium is dynamic?

A. The concentration of $Pb^{2+}(aq)$ ions remains constant.

B. The solution becomes radioactive.

C. The total mass of solid $PbCl_2$ increases.

D. The added radioactive solid remains unchanged.

A mixture of nitrogen dioxide ($NO_2(g)$) and dinitrogen tetroxide ($N_2O_4(g)$) is allowed to reach a state of dynamic equilibrium in a sealed container at constant temperature. The equation for the reaction is:

$2NO_2(g) \rightleftharpoons N_2O_4(g)$

Which statement is correct for this system at equilibrium?

A. The reaction has stopped.

B. The concentrations of $NO_2(g)$ and $N_2O_4(g)$ are equal.

C. The rate of formation of $N_2O_4(g)$ equals the rate of its decomposition.

D. The pressure of the system is no longer constant.

$1.0$ mol of water vapour, $H_2O(g)$, was placed in a sealed container and heated. The system was allowed to reach equilibrium at $1000$ K according to the following equation:

$2H_2O(g) \rightleftharpoons 2H_2(g) + O_2(g)$ $K_c = 7.3 \times 10^{-18}$ at $1000$ K

Which relationship is correct for this equilibrium at $1000$ K?

A. $[H_2O] = [H_2]$

B. $[H_2O] = 2[O_2]$

C. $[H_2O] << [H_2]$

D. $[H_2O] >> [H_2]$

The synthesis of ammonia from its elements is an important industrial process, and the following system is at equilibrium at a certain temperature:

$N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$

The equilibrium constant, $K_c$, for this reaction at this temperature is $0.55$.

What is the value of the equilibrium constant, $K_c$, for the decomposition of ammonia under the same conditions?

A. $0.55$

B. $\frac{1}{0.55}$

C. $\sqrt{0.55}$

D. $\frac{1}{\sqrt{0.55}}$