13.3 Shifting Equilibria: Le Châtelier’s Principle

The following equation represents a reversible decomposition:
$\text{CaCO}_{3} \left(s\right) \rightleftharpoons \text{CaO} \left(s\right) + \text{CO}_{2} \left(g\right)$

Under what conditions will decomposition in a closed container proceed to completion so that no CaCO₃ remains?

What property of a reaction can we use to predict the effect of a change in temperature on the value of an equilibrium constant?

The following reaction occurs when a burner on a gas stove is lit:
$\text{CH}_{4} \left(g\right) + 2 \text{O}_{2} \left(g\right) \rightleftharpoons \text{CO}_{2} \left(g\right) + 2 \text{H}_{2} \text{O} \left(g\right)$

Is an equilibrium among CH₄, O₂, CO₂, and H₂O established under these conditions? Explain your answer.

Suggest four ways in which the concentration of hydrazine, N₂H₄, could be increased in an equilibrium described by the following equation:
$\text{N}_{2} \left(g\right) + 2 \text{H}_{2} \left(g\right) \rightleftharpoons \text{N}_{2} \text{H}_{4} \left(g\right) \Delta H = 95 \text{kJ}$

How will an increase in temperature affect each of the following equilibria? How will a decrease in the volume of the reaction vessel affect each?

(a) $2 \text{NH}_{3} \left(g\right) \rightleftharpoons \text{N}_{2} \left(g\right) + 3 \text{H}_{2} \left(g\right) \Delta H = 92 \text{kJ}$

(b) $\text{N}_{2} \left(g\right) + \text{O}_{2} \left(g\right) \rightleftharpoons 2 \text{NO} \left(g\right) \Delta H = 181 \text{kJ}$

(c) $2 \text{O}_{3} \left(g\right) \rightleftharpoons 3 \text{O}_{2} \left(g\right) \Delta H = −285 \text{kJ}$

(d) $\text{CaO} \left(s\right) + \text{CO}_{2} \left(g\right) \rightleftharpoons \text{CaCO}_{3} \left(s\right) \Delta H = −176 \text{kJ}$

Methanol can be prepared from carbon monoxide and hydrogen at high temperature and pressure in the presence of a suitable catalyst.

(a) Write the expression for the equilibrium constant (K_c) for the reversible reaction
$2 \text{H}_{2} \left(g\right) + \text{CO} \left(g\right) \rightleftharpoons \text{CH}_{3} \text{OH} \left(g\right) \Delta H = −90.2 \text{kJ}$

(b) What will happen to the concentrations of H₂, CO, and CH₃OH at equilibrium if more H₂ is added?

(c) What will happen to the concentrations of H₂, CO, and CH₃OH at equilibrium…

Water gas, a mixture of H₂ and CO, is an important industrial fuel produced by the reaction of steam with red hot coke, essentially pure carbon.

(a) Write the expression for the equilibrium constant for the reversible reaction
$\text{C} \left(s\right) + \text{H}_{2} \text{O} \left(g\right) \rightleftharpoons \text{CO} \left(g\right) + \text{H}_{2} \left(g\right) \Delta H = 131.30 \text{kJ}$

(b) What will happen to the concentration of each reactant and product at equilibrium if more C is added?

(c) What will happen to the concentration of each reactant and pr…

Ammonia is a weak base that reacts with water according to this equation:
$\text{NH}_{3} \left(a q\right) + \text{H}_{2} \text{O} \left(l\right) \rightleftharpoons \text{NH}_{4} ^{+} \left(a q\right) + \text{OH}^{−} \left(a q\right)$

Will any of the following increase the percent of ammonia that is converted to the ammonium ion in water?

(a) Addition of NaOH

(b) Addition of HCl

(c) Addition of NH₄Cl

Suggest two ways in which the equilibrium concentration of Ag⁺ can be reduced in a solution of Na⁺, Cl⁻, Ag⁺, and $\text{NO}_{3} ^{−} ,$ in contact with solid AgCl.
$\text{Na}^{+} \left(a q\right) + \text{Cl}^{−} \left(a q\right) + \text{Ag}^{+} \left(a q\right) + \text{NO}_{3} ^{−} \left(a q\right) \rightleftharpoons \text{AgCl} \left(s\right) + \text{Na}^{+} \left(a q\right) + \text{NO}_{3} ^{−} \left(a q\right)$
$\Delta H = −65.9 \text{kJ}$

A solution is saturated with silver sulfate and contains excess solid silver sulfate:
$\text{Ag}_{2} \text{SO}_{4} \left(s\right) \rightleftharpoons 2 \text{Ag}^{+} \left(a q\right) + \text{SO}_{4} ^{2−} \left(a q\right)$

A small amount of solid silver sulfate containing a radioactive isotope of silver is added to this solution. Within a few minutes, a portion of the solution phase is sampled and tests positive for radioactive Ag⁺ ions. Explain this observation.