Deck 14: Principles of Chemical Equilibrium

Question 1

Explain the dynamic nature of equilibrium in terms of reversibility.

Answer 1

At equilibrium, the rates of the forward and reverse reactions are equal. An equilibrium expression relates the concentrations of reactants and products at equilibrium. Every elementary reaction that goes in the forward direction can also go in the reverse direction.

Question 2

Understand some of the properties of equilibrium constants.

Answer 2

Concentrations or partial pressures can usually be used in place of activities in equilibrium constant expressions. The activity of a pure solid or liquid is equal to 1.

Question 3

Relate the equilibrium position to thermodynamic quantities.

Answer 3

Reactions always move in the direction that minimizes the total free energy.

Question 4

Predict the effects on the equilibrium position of changing concentrations or temperature.

Question 5

Solve quantitative equilibrium problems.

Question 6

Perform equilibrium calculations on reactions in aqueous solution.

Question 7

A system in chemical equilibrium is characterized by one of the following:

A) molecules no longer undergo reactions of any kinds.
B) macroscopic changes are observed.
C) unaffected by changes in temperature.
D) unaffected by addition of catalyst.
E) concentrations are changing at a fixed constant rate.

Question 8

A flask is filled with hydrogen, oxygen and several mL of water. This flask is then connected to a flask containing oxygen gas consisting of only the ¹⁷O isotope at the same pressure as the first flask. Which of the following will not occur?

A) Some water will evaporate.
B) The ¹⁷O₂ will diffuse into the other flask.
C) Hydrogen and water vapour will diffuse into the second flask.
D) ¹⁷O will be incorporated into the water.
E) ¹⁶O₂ will diffuse into the second flask.

Question 9

The equilibrium constant

A) for an aqueous phase reaction is based on concentration of reactants and products.
B) for a gas phase reaction is based on pressures of the reactants and products.
C) is based on activities of all species.
D) is dependent on the initial concentrations of all species.
E) is dependent on the initial concentration of reactants only.

Question 10

When is a reaction at equilibrium?

A) when K = 1
B) when all concentrations are equal
C) when Q = 1
D) when all concentrations are equal to 1 M or 1 atm
E) when Q = K

Question 11

The copper (I) ion is a curious species. In aqueous solutions, there are a number of reactions that it can undergo; one is the reaction with other copper(I) ions:2 Cu⁺ (aq) Cu²⁺(aq) + Cu(s) Using the tabulated data, calculate the equilibrium constant for this reaction of Cu⁺ (aq) at 298 and predict whether it will increase or decrease with increasing temperature. Choose from the following.

A) 3.5 x 10⁴; increase
B) 1.2 x 10^6; decrease
C) 2.2 x 10⁷ increase
D) 2.2 x 10⁷ decrease
E) 3.5 x 10⁴ decrease

Question 12

Adding water to the reaction vessel in which the following reaction is occurring will result inBa(OH)₂.8H₂O_(s) + NH₄NO_3(s) $\rarr$ Ba(NO₃)_2(s) + H₂O_(l) + NH_3(aq)

A) no change.
B) reaction will shift right as the concentration of NH₃ is decreased.
C) reaction will shift to the left as more product is added.
D) reaction will shift to the right as more product is added.
E) reaction will shift left as the concentration of NH₃ is increased.

Question 13

If the dissolution of CaCl₂ is endothermic, will any of the following increase the amount of CaCl₂ that will dissolve in water?

A) addition of NaCl
B) addition of Ca(NO₃)₂
C) addition of HCl
D) increase in temperature
E) decrease in temperature

Question 14

Which of the following will decrease the amount of [NH₄][NO₃] that will dissolve in water?

A) addition of NaCl
B) addition of Ca(NO₃)₂
C) addition of HCl
D) addition of NaOH
E) increase the pressure

Question 15

A system containing nitrogen, ammonia, and hydrogen is at equilibrium. The exothermic reaction will shift to greater production of ammonia if

A) H₂ is added.
B) NH₃ is added.
C) Ar is added.
D) a catalyst is added.
E) the temperature is increased.

Question 16

Which way will the Haber process shift if a container at equilibrium has its volume decreased?
N₂ + 3 H₂ 2 NH₃

A) Shift to the reactants.
B) Shift to the products.
C) There will be no change.
D) The temperature will increase.
E) Initially will shift to the products, then readjust to original pressures.

Question 17

Which way will the Haber process (a spontaneous reaction) shift if the temperature of a container at equilibrium is raised?
N₂ + 3 H₂ 2 NH₃

A) Shift to the reactants.
B) Shift to the products.
C) There will be no change.
D) The rate of the reaction will increase.
E) Initially will shift to the products, then readjust to original pressures.

Question 18

When solving equilibrium problems the best way to simplify the problem is to

A) apply approximations.
B) use the quadratic equation.
C) approach equilibrium from the side from which the change is smallest.
D) divide by zero.
E) find the rate-determining step.

Question 19

When 0.1 mole of methylamine is dissolved in 500 mL of water, the following hydrolysis reaction occurs:
H₂O_(l) + CH₃NH_2(aq) CH₃NH₃⁺_(aq) + OH^-_(aq)
The hydroxide concentration is found to be 8.6 x10^-3 M when equilibrium is reached. What is the value of the equilibrium constant for this reaction?

A) 4.3 x 10^-2
B) 7.4 x10^-4
C) 7.4 x 10^-5
D) 3.9 x 10^-4
E) 7.4 x 10^-3

Question 20

When ammonia dissolves in water the new major species present are

A) H₂O; NH₂^-; H⁺
B) H₂O; NH₃
C) H₂O; NH₄⁺; OH^-
D) H₂O; NH^2-; H⁺
E) H₂O; N^3-; H⁺

Question 21

Addition of sodium mono-hydrogencarbonate to water gives what minor species?

A) H₂O; Na⁺; H⁺; CO₃^2-
B) H₂O; Na⁺; OH^-; H₂CO₃
C) H₂O; NaHCO₃
D) H₂O; Na⁺; H₃CO₃^+; OH^-
E) H₂O; Na⁺; HCO₃^-

Question 22

Addition of sodium mono-hydrogencarbonate to water gives what major species?

A) H₂O; H⁺; CO₃^2-
B) H⁺, CO₃^2-, OH^-; H₂CO₃
C) NaHCO₃
D) H₂O; Na⁺; H₂CO₃, OH^-
E) H₂O; Na⁺; HCO₃^-

Question 23

What are the minor species present upon adding the slightly soluble PbCl_2(s) to water?

A) H₂O; Pb⁺², Cl^-, Cl₂^2-
B) Pb⁺², Cl^-, Cl₂^2-
C) Pb⁺², Cl^-
D) H₂O; Pb⁺², Cl^-
E) PbCl₂(s)

Question 24

Ammonia and aqueous HCl are combined in an Erlenmeyer flask. Which of the following reactions occurs?

A) precipitation reaction
B) donation of a proton to water
C) dissociation of a complex
D) donation of a proton to a base
E) dissolution of a salt in water

Question 25

Classify the equilibrium constant for the following reaction as:
Ag⁺_(aq) + 2 NH_3(aq) Ag(NH₃)₂⁺_(aq)

A) K_sp
B) K_ion
C) K_f
D) K_a
E) K_b

Question 26

Classify the equilibrium constant for the following reaction as:
CH₃NH_2(aq) + H₂O_(l) CH₃NH₃⁺_(aq) + OH^-_(aq)

A) K_sp
B) K_ion
C) K_f
D) K_a
E) K_b

Question 27

Classify the equilibrium constant for the following reaction as:
Fe(OH)_3(s) Fe⁺³_(aq) + 3 OH^-_(aq)

A) K_sp
B) K_ion
C) K_f
D) K_a
E) Kb

Question 28

In the manufacture of ammonia, nitrogen molecules dissociate to give nitrogen atoms on the surface of the catalyst. Draw a molecular picture showing the reverse of this process.

Question 29

Draw a graph of concentration vs. time for a system containing cis- and trans-butene in equilibrium (assume the equilibrium constant is 3.0) to which is added an amount of trans-butene equal to that present in the original mixture and monitored until equilibrium is reached again.

Question 30

Acetic acid dissolves in water and undergoes the following reaction to increase the concentration of hydronium ions:
CH₃COOH (aq) $\rightarrow$ H₃O⁺ (aq) + CH₃COO^- (aq)
k₁Express the equilibrium constant in terms of the rate constants of this elementary process and its reverse.
H₃O⁺ (aq) + CH₃COO^- (aq) $\rightarrow$ CH₃COOH (aq) k_-1

Question 31

What is the concentration based equilibrium constant for
4NO₂(g) + O₂(g) $\rightarrow$ 2N₂O₅(g)?

Question 32

Write the equilibrium constant expression for the following reaction:
2 N₂ (g) + 2O₂ (g) 4 NO (g)

Question 33

Write the equilibrium constant expression for the following reaction:
C₂H₄ (g) + 2HCl (g) + $\frac{1}{2}$ O₂ (g) CH₂ClCH₂Cl (g) + H₂O (g)

Question 34

Write the equilibrium constant expressions for the following reaction:
N₂(g) + 3 H₂(g) 2 NH₃(g)

Question 35

Write the equilibrium constant expression and state the reference concentrations for the reaction:
CaCO₃(s) CaO(s) + CO₂(g)

Question 36

Write the equilibrium constant expressions and state the reference concentrations for the reactants and products:
Cl₂ (g) + 2 H₂O (l ) HOCl (aq) + Cl^- (aq) + H₃O⁺ (aq)

Question 37

Write the equilibrium constant expression for the following reaction:
HCOOH_(aq) + H₂O_(l) H₃O⁺_(aq) + HCOO^-1_(aq)

Question 38

Write the equilibrium constant expression for the following reaction in terms of concentrations:
2 PbS_(s) + 3 O_2(g) 2 PbO_(s) + 2 SO_2(g)

Question 39

Write the combined equilibrium constant expression for the following proposed reaction mechanism of the reaction between NO₂ and CO:NO_2(g) + NO_2(g) NO_3(g) + NO_(g)
NO_3(g) + CO_(g) CO_2(g) + NO_2(g)

Question 40

The equilibrium constant for the following reaction is given:
4 NO_2(g) 2 N₂O_(g) + 3 O_2(g) K₁ = 690What is the value for the equilibrium constant of the reverse reaction?
2 N₂O_(g) + 3 O_2(g) 4 NO_2(g) K₂ =?

Question 41

Based on the following two reactions and equilibrium constants, determine the value of K₃.
I. NO_(g) + ½ O_2(g) NO_2(g) $\quad$ K₁ = 1.3 x 10⁶
II. ½ N_2(g) + ½ O_2(g) NO_(g) $\quad$ K₂ = 6.5 x 10^-16
N_2(g) + 2 O_2(g) 2 NO_2(g) $\quad$$\quad$ K₃ =?

Question 42

Calculate the equilibrium constant for the oxychlorination of ethylene to vinyl chloride, CH₂CHCl, under standard conditions at 100^oC given the thermodynamic data below collected at 25^oC:
$\Delta$ G° = 53.6(CH₂CHCl), -95.3(HCl), 68.49(CH₂CH₂), -228.7(H₂O) kJ/mol
$\Delta$ H° = 37.2(CH₂CHCl), -92.3(HCl), 52.4(CH₂CH₂), -241.8(H₂O) kJ/mol
The equation of reaction is:
CH₂CH_{2 (g)} + HCl _(g) + $\frac{1}{2}$ O_{2 (g)} $\rarr$ CH₂CHCl _(g) + H₂O _(g)

Question 43

The dehydration of benzyl alcohol to benzaldehyde is shown below:C₆H₅CH₂OH_(g) C₆H₅CHO_(g) + H_2(g)The equilibrium constant for this process is 0.558 at 525 K. 0.2 moles of benzyl alcohol is placed in a 2L flask with 0.15 moles benzaldehyde and 0.1 moles of H₂ gas. Determine Q for this mixture and which direction the reaction will shift to reach equilibrium.

Question 44

Calcite, CaCO_3(s), can be converted to CaO_(s) and CO_2(g). Determine the equilibrium constant at 25^oC and predict whether equilibrium favours the products or the reactants.

Question 45

Calcite, CaCO_3(s), can be converted to CaO_(s) and CO_2(g). What is the equilibrium pressure of CO₂ at 1150ºK?

Question 46

Determine the equilibrium constant at 0^oC for the following unbalanced reaction:Ba(OH)₂.08H₂O_(s) + NH₄NO_3(s) $\rightarrow$ Ba(NO₃)_2(s) + H₂O_(l) + NH_3(aq)

Question 47

The "water gas shift reaction" is shown below. Calculate K at (a) 1000ºK and (b) find the temperature at which the equilibrium constant is 1.CO (g) + H₂O (g) CO₂ (g) + H₂ (g)

Question 48

Consider the dissociation of mono-hydrogen carbonate to carbonate and aqueous hydrogen ion:H₂O_(l) + HCO₃^- (aq) H₃O⁺ (aq) + CO₃^2- (aq)ΔG˚ = (-237.1) (-586.77) (-237.1) (-527.8) kJ/mol
a) Calculate ∆G° for this reaction.
b) Calculate ∆G for the same reaction, where [CO₃^2-]=[HCO₃^-] = 1 M and [H⁺] = 1 x 10^-11 M. Under which conditions will this reaction be spontaneous?

Question 49

Water undergoes dissociation as shown below:
2 H₂O (aq) H₃O⁺ (aq) + OH^- (aq)
?G? = (-237.1) (-237.1) (-157.244) kJ/mole
Find K for this reaction at 25?C and 99?C.

Question 50

Lead chloride is not very soluble in water:
PbCl₂ (s) Pb²⁺(aq) + 2 Cl^- (aq) Using the tabulated data, find the equilibrium constants for dissolution of PbCl₂ at 298º and 372ºK, respectively.

Question 51

H₂PO₄^-1 is commonly used in making buffer solutions with a pH near your body's pH. Given that K_a = 6.2 x10^-8 at 25˚C for the following acid-base reaction, determine ΔG˚:H₂PO₄^-1_(aq) + H₂O_(l) HPO₄^-2_(aq) + H₃O⁺_(aq)

Question 52

Predict whether each equilibrium reaction will shift toward products or reactants with a decrease in temperature.(a) CH₄ + H₂O CO + 3 H₂ ∆H° = 206 kJ(b) 2 SO₂ + O₂ 2 SO₃ ∆H° = - 198 kJ

Question 53

What will be the shift in equilibrium for the following reaction upon increasing temperature?N₂ (g) + O₂ (g) 2 NO (g) ∆H° = 90.3 kJ

Question 54

A system containing nitrogen, ammonia and hydrogen is at equilibrium. If the partial pressures of the gases remain the same immediately upon addition of Ar, what will the equilibrium do to re-establish equilibrium?
N₂ + 3 H₂ 2 NH₃

Question 55

Water undergoes self dissociation as below:
2 H₂O (aq) H₃O⁺ (aq) + OH^- (aq)
If K increases as temperature increases, determine if this reaction is endothermic or exothermic and explain.

Question 56

A sample of 3.00 x 10^-1 mole of pure phosgene gas, COCl₂, was placed in a 15.0 L container and heated to 800ºK. At equilibrium, the partial pressure of CO was found to be 0.497 bar. Calculate the equilibrium constant for the following reaction:COCl_{2 (g)} CO _(g) + Cl_{2 (g)}

Question 57

A sample of pure phosgene, COCl₂, is placed in a 15.0 L container which is subsequently heated to 800ºK. The equilibrium constant for the decomposition of phosgene at 800ºK is 0.297, and the equilibrium mixture contains 1.1 x 10^-1 moles of Cl₂(g), what are the equilibrium partial pressures of phosgene and carbon monoxide and how many moles of phosgene were placed in the original sample?COCl_{2 (g)} CO _(g) + Cl_{2 (g)}

Question 58

The conversion of nitrogen and hydrogen to ammonia is an important industrial reaction:N_{2 (g)} + 3 H_{2 (g)} 2 NH_{3 (g)}If a tank initially containing only nitrogen at 1.0 atm and hydrogen at 3.0 atm converts 13.0 % of the nitrogen to ammonia, what is the value of the equilibrium constant for the reaction at this temperature?

Question 59

Heating isopropyl alcohol causes it to break down to acetone and hydrogen gas:(CH₃)₂CHOH_(g) (CH₃)₂CO_(g) + H_2(g)At 180˚C, the equilibrium constant is 0.444 for this dehydrogenation reaction. If 10.0 grams of isopropyl alcohol is placed in a 10.0-L vessel and heated, what will be the partial pressure of acetone when equilibrium is reached?

Question 60

Heating isopropyl alcohol causes it to break down to acetone and hydrogen gas:(CH₃)₂CHOH_(g) (CH₃)₂CO_(g) + H_2(g)If 20.0 g of isopropyl alcohol is placed in a 20.0 L vessel and heated to 180^oC, the partial pressure of acetone stabilizes at 0.35 atm. What is the equilibrium constant?

Question 61

Heating isopropyl alcohol causes it to break down to acetone and hydrogen gas:(CH₃)₂CHOH_(g) (CH₃)₂CO_(g) + H_2(g)If 20.0 g of isopropyl alcohol is placed in a 20.0 L vessel and heated to 180^oC. The final pressure in the vessel is 0.96 atm, what is the equilibrium constant?

Question 62

The water gas shift reaction is used to remove CO from the mixture of gases in ammonia production:CO _(g) + H₂O _(g) CO_{2 (g)} + H_{2 (g)}At 300°C, the equilibrium constant for this reaction has K = 36. If a tank with a volume of 30.0 L is charged with 1.0 mole of CO and 2.2 mols of H₂O and the temperature brought to 300°C, what are the equilibrium pressures of CO, H₂, H₂O and CO₂ in the tank?

Question 63

At 1033ºK, K = 33.3 M for the equilibrium reaction:PCl_{5 (g)} PCl_{3 (g)} + Cl_{2 (g)}If a mixture of 0.100 mole of PCl₅ and 0.300 mole of PCl₃ is placed in a 2.00 L reaction vessel and heated to 1033ºK, what are the numbers of mols of each component at equilibrium?

Question 64

HCO₃^-1 is used by your body to maintain pH levels in the blood. If the original concentration of [HCO₃^-1] = 0.0020M, determine the concentration of H₃O⁺ given K_eq = 4.7 x10^-11.HCO₃^-1_(aq) + H₂O_(l) H₃O⁺_(aq) + CO₃^-2_(aq)

Question 65

A solution contains 0.01 M Ag and 0.1 M Pb²⁺. NaCl is gradually added to precipitate the Ag⁺ as AgCl, and the Pb²⁺ as PbCl₂. Given the following K_sp values: AgCl (K_sp = 1.6 x 10^-10) PbCl₂ (K_sp = 2.4 x 10^-4). What is the concentration of Ag⁺ when the Pb²⁺ begins to precipitate?

Question 66

The K_sp of PbBr₂ is 8.9 x 10^-6. If enough PbBr₂ salt is added to saturate the following solutions, determine the equilibrium concentration of Pb²⁺ in pure water and in 0.20 M KBr.

Question 67

Solid CaF₂ is added to a 0.10 M solution of CaCl₂ until no more will dissolve. If the K_sp of CaF₂ is 3.9 x 10^-11 M³, what are the concentrations of Ca²⁺ _(aq) and F^-_(aq) at equilibrium?

Question 68

A sample of 0.134 g of CuCl₂•2H₂O is added to 0.10 L of an 1.0 M ammonia solution. It completely dissolves to give aqueous Cu²⁺ ions which react with the ammonia to form the coppertetraammine complex ion:Cu²⁺ _(aq) + 4 NH_{3 (aq)} Cu(NH₃)₄²⁺_(aq) K_f = 5.0 x 10¹³What are the concentrations of copper (II), ammonia, and the complex ion, Cu(NH₃) ₄²⁺, at equilibrium?

Question 69

What are the major species present upon dissolving glucose (C₆H₁₂O₆) in water?

Question 70

Solid silver chloride is added to two beakers, one containing 0.5 M NaNO₃ and the other 0.5 M NaCl. In which will the silver ion concentration be higher?