13.3 Shifting equilibria: le châtelier’s principle  (Page 7/10)

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) $2{\text{H}}_2\text{O}(g)\rightleftharpoons 2{\text{H}}_2(g)+{\text{O}}_2(g)\text{Δ}H=484\text{kJ}$

(b) ${\text{N}}_2(g)+3{\text{H}}_2(g)\rightleftharpoons 2{\text{NH}}_3(g)\text{Δ}H=\mathrm{-92.2}\text{kJ}$

(c) $2\text{Br}(g)\rightleftharpoons {\text{Br}}_2(g)\text{Δ}H=\mathrm{-224}\text{kJ}$

(d) ${\text{H}}_2(g)+{\text{I}}_2(s)\rightleftharpoons 2\text{HI}(g)\text{Δ}H=53\text{kJ}$

Water gas is a 1:1 mixture of carbon monoxide and hydrogen gas and is called water gas because it is formed from steam and hot carbon in the following reaction: ${\text{H}}_2\text{O}(g)+\text{C}(s)\rightleftharpoons {\text{H}}_2(g)+\text{CO}(g).$ Methanol, a liquid fuel that could possibly replace gasoline, can be prepared from water gas 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
$2{\text{H}}_2(g)+\text{CO}(g)\rightleftharpoons {\text{CH}}_3\text{OH}(g)\text{Δ}H=\mathrm{-90.2}\text{kJ}$

(b) What will happen to the concentrations of H ₂ , CO, and CH ₃ OH at equilibrium if more H ₂ is added?

(c) What will happen to the concentrations of H ₂ , CO, and CH ₃ OH at equilibrium if CO is removed?

(d) What will happen to the concentrations of H ₂ , CO, and CH ₃ OH at equilibrium if CH ₃ OH is added?

(e) What will happen to the concentrations of H ₂ , CO, and CH ₃ OH at equilibrium if the temperature of the system is increased?

(f) What will happen to the concentrations of H ₂ , CO, and CH ₃ OH at equilibrium if more catalyst is added?

Nitrogen and oxygen react at high temperatures.

(a) Write the expression for the equilibrium constant ( K _c ) for the reversible reaction
${\text{N}}_2(g)+{\text{O}}_2(g)\rightleftharpoons 2\text{NO}(g)\text{Δ}H=181\text{kJ}$

(b) What will happen to the concentrations of N ₂ , O ₂ , and NO at equilibrium if more O ₂ is added?

(c) What will happen to the concentrations of N ₂ , O ₂ , and NO at equilibrium if N ₂ is removed?

(d) What will happen to the concentrations of N ₂ , O ₂ , and NO at equilibrium if NO is added?

(e) What will happen to the concentrations of N ₂ , O ₂ , and NO at equilibrium if the pressure on the system is increased by reducing the volume of the reaction vessel?

(f) What will happen to the concentrations of N ₂ , O ₂ , and NO at equilibrium if the temperature of the system is increased?

(g) What will happen to the concentrations of N ₂ , O ₂ , and NO at equilibrium if a catalyst is added?

Water gas, a mixture of H ₂ 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
$\text{C}(s)+{\text{H}}_2\text{O}(g)\rightleftharpoons \text{CO}(g)+{\text{H}}_2(g)\text{Δ}H=131.30\text{kJ}$

(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 product at equilibrium if H ₂ O is removed?

(d) What will happen to the concentration of each reactant and product at equilibrium if CO is added?

(e) What will happen to the concentration of each reactant and product at equilibrium if the temperature of the system is increased?

Pure iron metal can be produced by the reduction of iron(III) oxide with hydrogen gas.

(a) Write the expression for the equilibrium constant ( K _c ) for the reversible reaction
${\text{Fe}}_2{\text{O}}_3(s)+3{\text{H}}_2(g)\rightleftharpoons 2\text{Fe}(s)+3{\text{H}}_2\text{O}(g)\text{Δ}H=98.7\text{kJ}$

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

(c) What will happen to the concentration of each reactant and product at equilibrium if H ₂ O is removed?

(d) What will happen to the concentration of each reactant and product at equilibrium if H ₂ is added?

(e) What will happen to the concentration of each reactant and product at equilibrium if the pressure on the system is increased by reducing the volume of the reaction vessel?

(f) What will happen to the concentration of each reactant and product at equilibrium if the temperature of the system is increased?

Ammonia is a weak base that reacts with water according to this equation:
${\text{NH}}_3(aq)+{\text{H}}_2\text{O}(l)\rightleftharpoons {\text{NH}}_4{}^{\text{+}}(aq)+{\text{OH}}^{\text{−}}(aq)$

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 NH ₄ Cl

Acetic acid is a weak acid that reacts with water according to this equation:
${\text{CH}}_3{\text{CO}}_2\text{H}(aq)+{\text{H}}_2\text{O}(aq)\rightleftharpoons {\text{H}}_3{\text{O}}^{\text{+}}(aq)+{\text{CH}}_3{\text{CO}}_2{}^{\text{−}}(aq)$

Will any of the following increase the percent of acetic acid that reacts and produces ${\text{CH}}_3{\text{CO}}_2{}^{\text{−}}$ ion?

(a) Addition of HCl

(b) Addition of NaOH

(c) Addition of NaCH ₃ CO ₂

Suggest two ways in which the equilibrium concentration of Ag ⁺ can be reduced in a solution of Na ⁺ , Cl ⁻ , Ag ⁺ , and ${\text{NO}}_3{}^{\text{−}},$ in contact with solid AgCl.
${\text{Na}}^{\text{+}}(aq)+{\text{Cl}}^{\text{−}}(aq)+{\text{Ag}}^{\text{+}}(aq)+{\text{NO}}_3{}^{\text{−}}(aq)\rightleftharpoons \text{AgCl}(s)+{\text{Na}}^{\text{+}}(aq)+{\text{NO}}_3{}^{\text{−}}(aq)$
$\text{Δ}H=\mathrm{-65.9}\text{kJ}$

How can the pressure of water vapor be increased in the following equilibrium?
${\text{H}}_2\text{O}(l)\rightleftharpoons {\text{H}}_2\text{O}(g)\text{Δ}H=41\text{kJ}$

Additional solid silver sulfate, a slightly soluble solid, is added to a solution of silver ion and sulfate ion at equilibrium with solid silver sulfate.
$2{\text{Ag}}^{\text{+}}(aq)+{\text{SO}}_4{}^{\mathrm{2-}}(aq)\rightleftharpoons {\text{Ag}}_2{\text{SO}}_4(s)$

Which of the following will occur?

(a) Ag ⁺ or ${\text{SO}}_4{}^{\mathrm{2-}}$ concentrations will not change.

(b) The added silver sulfate will dissolve.

(c) Additional silver sulfate will form and precipitate from solution as Ag ⁺ ions and ${\text{SO}}_4{}^{\mathrm{2-}}$ ions combine.

(d) The Ag ⁺ ion concentration will increase and the ${\text{SO}}_4{}^{\mathrm{2-}}$ ion concentration will decrease.

The amino acid alanine has two isomers, α-alanine and β-alanine. When equal masses of these two compounds are dissolved in equal amounts of a solvent, the solution of α-alanine freezes at the lowest temperature. Which form, α-alanine or β-alanine, has the larger equilibrium constant for ionization $(\text{HX}\rightleftharpoons {\text{H}}^{\text{+}}+{\text{X}}^{\text{−}})$ ?