Deck 17: Equilibrium: the Extent of Chemical Reactions

Question 1

Write the mass-action expression, Q_c , for the following chemical reaction. Zn(s) + 2Ag⁺(aq) Zn²⁺(aq) + 2Ag(s)

A)
B)
C)
D)
E)

Answer 1

Question 2

The two equilibrium constants for the same reaction, K_c and K_p, will always equal one another when

A) all of the reactants and products are gases.
B) in the reaction equation, the number of moles of gaseous products equals the number of moles of gaseous reactants.
C) in the reaction equation, the number of moles of gaseous products is greater than the number of moles of gaseous reactants.
D) in the reaction equation, the number of moles of gaseous products is smaller than the number of moles of gaseous reactants.
E) in the reaction equation, the total number of moles of reactants equals that of the products.

Answer 2

in the reaction equation, the number of moles of gaseous products equals the number of moles of gaseous reactants.

Question 3

Write the mass-action expression, Q_c , for the following chemical reaction. Fe³⁺(aq) + 3OH^-(aq) Fe(OH)₃(s)

A)
B)
C)
D)
E)

Answer 3

Question 4

Carbon monoxide and chlorine combine in an equilibrium reaction to produce the highly toxic product, phosgene (COCl₂) CO(g) + Cl₂(g)
COCl₂(g)
If the equilibrium constant for this reaction is K_c = 248, predict, if possible, what will happen when the reactants and product are combined with the concentrations shown.
[CO] = [Cl₂] = 0.010 M; [COCl₂] = 0.070 M

A) The reaction will proceed to the right.
B) The reaction will proceed to the left.
C) The reaction is at equilibrium, and no change in concentrations will occur.
D) The container volume needs to be specified before a prediction can be made.
E) The temperature needs to be specified before a prediction can be made.

Question 5

An equilibrium is established in which both the forward (fwd) and the reverse (rev) reactions are elementary. If the equilibrium constant K_c = 1.6 × 10^-2 and the rate constant k_fwd = 8.0 × 10^-7 s^-1 what is the value of k_rev?

A) 1.3 × 10^-8 s^-1
B) 7.8 × 10⁷ s^-1
C) 2 × 10⁴ s^-1
D) 5.0 × 10^-5 s^-1
E) none of the above

Question 6

The reaction quotient for a gas phase reaction has a value of 2000. If the number of moles of reactants in the reaction equation is equal to that of the products, which of the following statements is definitely true?

A) The reaction must proceed to the left to establish equilibrium.
B) The reaction must proceed to the right to establish equilibrium.
C) When the system is at equilibrium, the concentrations of the products will be much larger than the concentrations of the reactants.
D) The concentrations of the products are generally larger than the concentrations of the reactants.
E) None of the above statements is true.

Question 7

Write the mass-action expression, Q_c , for the following chemical reaction. 3ClO₂^-(aq) 2ClO₃^-(aq) + Cl^-(aq)

A)
B)
C)
D)
E)

Question 8

What is the mass-action expression, Q_c , for the following chemical reaction? Cu²⁺(aq) + 4NH₃(aq) Cu(NH₃)₄²⁺(aq)

A)
B)
C)
D)
E) None of the above is the correct mass-action expression.

Question 9

What is the mass-action expression, Q_p, for the following reaction? SbF₅(g) + 4Cl₂(g) SbCl₃(g) + 5ClF(g)

A)
B)
C)
D)
E) None of the above is the correct mass-action expression.

Question 10

Which of the following has an effect on the magnitude of the equilibrium constant?

A) removing products as they are formed
B) adding more of a reactant
C) adding a catalyst
D) increasing the pressure, in a gas-phase reaction
E) change in temperature

Question 11

Write the mass-action expression, Q_c, for the following chemical reaction equation. 2C₆H₆(g) + 15O₂(g) 12CO₂(g) + 6H₂O(g)

A)
B)
C)
D)
E)

Question 12

Write the mass-action expression, Q_c, for the following chemical reaction. NO(g) + Br₂(g) NOBr(g)

A)
B)
C)
D)
E)

Question 13

A chemical reaction has an equilibrium constant of 2 × 10⁶. If this reaction is at equilibrium, select the one correct conclusion that can be made about the reaction.

A) The forward and back reactions have stopped.
B) The limiting reactant has been used up.
C) The forward and reverse rate constants are equal.
D) The forward and reverse reaction rates are equal.
E) None of the above conclusions is correct.

Question 14

What is the mass-action expression, Q_c , for the following chemical reaction? PbO(s) + CO(g) Pb(l) + CO₂(g)

A)
B)
C)
D)
E) None of the above expressions is correct.

Question 15

The reaction quotient, Q_c, for a reaction has a value of 75 while the equilibrium constant, K_c, has a value of 195. Which of the following statements is accurate?

A) The reaction must proceed to the left to establish equilibrium.
B) The reaction must proceed to the right to establish equilibrium.
C) The concentrations of the products will be much smaller than the concentrations of the reactants when the system is at equilibrium.
D) The concentrations of the products will be about the same as the concentrations of the reactants when the system is at equilibrium.
E) None of the above statements is accurate.

Question 16

In order to write the correct mass-action expression for a reaction one must

A) know the kinetic rate law for the reaction.
B) know the mechanism for the reaction.
C) have a properly balanced chemical equation.
D) have values for the concentrations of the reactants.
E) know the limiting reactant.

Question 17

Carbon monoxide and chlorine combine in an equilibrium reaction to produce the highly toxic product, phosgene (COCl₂) CO(g) + Cl₂(g)
COCl₂(g)
If the equilibrium constant for this reaction is K_c = 248, predict, if possible, what will happen when the reactants and product are combined with the concentrations shown.
[CO] = [Cl₂] = 0.0200 M; [COCl₂] = 0.0992 M

A) The reaction will proceed to the right.
B) The reaction will proceed to the left.
C) The reaction is at equilibrium, and no change in concentrations will occur.
D) The container volume needs to be specified before a prediction can be made.
E) The temperature needs to be specified before a prediction can be made.

Question 18

Consider the equilibrium reaction shown below. B₂(g)
2B(g)
If the rate constants are: k_fwd = 7.00 × 10^-5 s^-1 and k_rev = 2.00 × 10^-5 L mol^-1 s^-1, what is the value of K_c under these conditions?

A) 1.75 × 10⁵
B) 3.50
C) 0.286
D) 5.71 × 10^-6
E) 1.40 × 10^-10

Question 19

When a chemical system is at equilibrium,

A) the concentrations of the reactants are equal to the concentrations of the products.
B) the concentrations of the reactants and products have reached constant values.
C) the forward and reverse reactions have stopped.
D) the reaction quotient, Q, has reached a maximum.
E) the reaction quotient, Q, has reached a minimum.

Question 20

Write the mass-action expression, Q_c , for the following chemical reaction. 2Cu²⁺(aq) + 4I^-(aq) 2CuI(s) + I₂(aq)

A)
B)
C)
D)
E)

Question 21

What is the mass-action expression, Q_c , for the following chemical reaction? 4H₃O⁺(aq) + 2Cl^-(aq) + MnO₂(s) Mn²⁺(aq) + 6H₂O(l) + Cl₂(g)

A)
B)
C)
D)
E) None of the above expressions is correct.

Question 22

The equilibrium constant for reaction (1) below is 276. Under the same conditions, what is the equilibrium constant of reaction (2)? (1) X₂(g) + Y₂(g) XY(g)
(2) 2XY(g) X₂(g) + Y₂(g)

A) 6.02 × 10^-2
B) 7.25 × 10^-3
C) 3.62 × 10^-3
D) 1.31 × 10^-5
E) none of the above

Question 23

N₂(g) + O₂(g) 2NO(g) K_c = 4.8 × 10^-31
2NOBr(g)
2NO(g) + Br₂(g) K_c = 0.50
Given the above equilibrium constant data at 25 °C, what is the value of K_c at this temperature for the reaction
2NOBr(g)
N₂(g) + O₂(g) + Br₂(g)?

A) 2.4 × 10^-31
B) 9.6 × 10^-31
C) 1.0 × 10³⁰
D) 4.2 × 10³⁰
E) none of the above

Question 24

Consider the reactions of cadmium with the thiosulfate anion. Cd²⁺(aq) + S₂O₃^2-(aq) Cd(S₂O₃)(aq) K₁ = 8.3 × 10³
Cd(S₂O₃)(aq) + S₂O₃^2-(aq) Cd(S₂O₃)₂^2-(aq) K₂ = 2.5 × 10²
What is the value for the equilibrium constant for the following reaction?
Cd²⁺(aq) + 2S₂O₃^2-(aq) Cd(S₂O₃)₂^2-(aq)

A) 0.030
B) 33
C) 8.1 × 10³
D) 8.6 × 10³
E) 2.1 × 10⁶

Question 25

H₂SO₃(aq) HSO₃^-(aq) + H⁺(aq) K_c = 1.4 × 10^-2
H₂SO₃(aq)
SO₃^2-(aq) + 2H⁺(aq) K_c = 9.1 × 10^-10
Given the above equilibrium constant data at 25 °C, what is the value of K_c at this temperature for the reaction
HSO₃^-(aq)
SO₃^2-(aq) + H⁺(aq)?

A) 6.5 × 10^-8
B) 1.3 × 10^-11
C) 7.8 × 10¹⁰
D) 1.5 × 10⁷
E) none of the above

Question 26

The equilibrium constant, K_p , for the reaction H₂(g) + I₂(g) 2HI(g)
Is 55.2 at 425°C. A rigid cylinder at that temperature contains 0.127 atm of hydrogen, 0.134 atm of iodine, and 1.055 atm of hydrogen iodide. Is the system at equilibrium?

A) Yes.
B) No, the forward reaction must proceed to establish equilibrium.
C) No, the reverse reaction must proceed to establish equilibrium.
D) Need to know the volume of the container before deciding.
E) Need to know the starting concentrations of all substances before deciding.

Question 27

About half of the sodium carbonate produced is used in making glass products because it lowers the melting point of sand, the major component of glass. When sodium carbonate is added to water it hydrolyses according to the following reactions. CO₃^2-(aq) + H₂O(l) HCO₃^-(aq) + OH^-(aq) K₁
HCO₃^-(aq) + H₂O(l) H₂CO₃(aq) + OH^-(aq) K₂
These can be combined to yield
CO₃^2-(aq) + 2H₂O(l) H₂CO₃(aq) + 2OH^-(aq) K₃
What is the value of K₃?

A) K₁ × K ₂
B) K₁ ÷ K ₂
C) K ₁ + K ₂
D) K ₁ - K ₂
E) (K₁K₂)²

Question 28

In water, the following equilibrium exists: H⁺(aq) + OH^-(aq)
H₂O(l)
In pure water at 25 °C, the concentration of H⁺ ions is 1.00 × 10^-7 mol/L. Calculate the value of the equilibrium constant for the reaction as written above.

A) 1.00 × 10¹⁴
B) 1.00 × 10¹²
C) 1.00 × 10^-14
D) 1.00 × 10^-12
E) 5.55 × 10¹⁵

Question 29

The equilibrium constant for the reaction of bromine with chlorine to form bromine monochloride is 58.0 at a certain temperature. Br₂(g) + Cl₂(g) 2BrCl(g)
What is the equilibrium constant for the following reaction?
BrCl(g) Br₂(g) + Cl₂(g)

A) 2.97 × 10^-4
B) 1.72 × 10^-2
C) 3.45 × 10^-2
D) 1.31 × 10^-1
E) > 1.00

Question 30

Nitrogen dioxide decomposes according to the reaction 2NO₂(g) 2NO(g) + O₂(g)
Where K_p = 4.48 × 10^-13 at 25°C. What is the value for K_c?

A) 1.81 × 10^-16
B) 1.83 × 10^-14
C) 4.48 × 10^-13
D) 1.10 × 10^-11
E) 1.11 × 10^-9

Question 31

Write the mass-action expression, Q_c , for the following chemical reaction. Sn²⁺(aq) + O₂(g) + 3H₂O(l) SnO₂(s) + 2H₃O⁺(aq)

A)
B)
C)
D)
E) None of the above expressions is correct.

Question 32

The equilibrium constant, K_p, has a value of 6.5 × 10^-4 at 308 K for the reaction of nitrogen monoxide with chlorine. 2NO(g) + Cl₂(g) 2NOCl(g)
What is the value of K_c?

A) 2.5 × 10^-7
B) 6.5 × 10^-4
C) 1.6 × 10^-2
D) 1.7
E) none of the above

Question 33

Consider the following two equilibria and their respective equilibrium constants: (1) NO(g) + O₂(g) NO₂(g)
(2) 2NO₂(g) 2NO(g) + O₂(g)
Which one of the following is the correct relationship between the equilibrium constants K₁ and K₂?

A) K₂ = 2/K₁
B) K₂ = (1/K₁)²
C) K₂ = -K₁/2
D) K₂ = 1/(2K₁)
E) K₂ = 1/(2K₁)²

Question 34

Hydrogen sulfide will react with water as shown in the following reactions. H₂S(g) + H₂O(l) H₃O⁺(aq) + HS^-(aq) K₁ = 1.0 × 10^-7
HS^-(aq) + H₂O(l) H₃O⁺(aq) + S^2-(aq) K₂ = ?
H₂S(g) + 2H₂O(l) 2H₃O⁺(aq) + S^2-(aq) K₃ = 1.3 × 10^-20
What is the value of K₂?

A) 1.3 × 10^-27
B) 2.3 × 10^-7
C) 1.3 × 10^-13
D) 7.7 × 10¹²
E) 7.7 × 10²⁶

Question 35

At 500°C the equilibrium constant, K_p , is 4.00 × 10^-4 for the equilibrium: 2HCN(g) H₂(g) + C₂N₂(g)
What is K_p for the following reaction?
H₂(g) + C₂N₂(g) 2HCN(g)

A) 2.00 × 10^-4
B) -4.00 × 10^-4
C) 1.25 × 10³
D) 2.50 × 10³
E) 4.00 × 10⁴

Question 36

The equilibrium constant, K_c , for the decomposition of COBr₂ COBr₂(g) CO(g) + Br₂(g)
Is 0.190. What is K_c for the following reaction?
2CO(g) + 2Br₂(g) 2COBr₂(g)

A) 0.0361
B) 2.63
C) 5.62
D) 10.5
E) 27.7

Question 37

Consider the equilibrium reaction: N₂O₄(g) 2NO₂(g) Which of the following correctly describes the relationship between K_c and K_p for the reaction?

A) K_p = K_c
B) K_p = RT × K_c
C) K_p = (RT × K_c)^-1
D) K_p = K_c /RT
E) K_p = RT/K_c

Question 38

The reaction of nitrogen with oxygen to form nitrogen monoxide can be represented by the following equation. N₂(g) + O₂(g) 2NO(g)
At 2000°C, the equilibrium constant, K_c , has a value of 4.10 × 10^-4. What is the value of K_p?

A) 2.17 × 10^-8
B) 4.10 × 10^-4
C) 7.65 × 10^-2
D) 7.75
E) none of the above

Question 39

Consider the equilibrium reaction: H₂(g) + Br₂(g) 2HBr(g) Which of the following correctly describes the relationship between K_c and K_p for the reaction?

A) K_p = K_c
B) K_p = (RT)K_c
C) K_p = (RT)²K_c
D) K_p = K_c/RT
E) K_p = K_c/(RT)²

Question 40

Write the mass-action expression, Q_c , for the following chemical reaction. MgO(s) + SO₂(g) + O₂(g) MgSO₄(s)

A)
B)
C)
D)
E) None of the above expressions is correct.

Question 41

At 25°C, the equilibrium constant K_c for the reaction 2A(g) B(g) + C(g)
Is 0.035. A mixture of 8.00 moles of B and 12.00 moles of C in a 20.0 L container is allowed to come to equilibrium. What is the equilibrium concentration of A?

A) < 0.100 M
B) 0.339 M
C) 0.678 M
D) 6.78 M
E) 13.56 M

Question 42

The reaction system POCl₃(g) POCl(g) + Cl₂(g)
Is at equilibrium. Which of the following statements describes the behavior of the system if the partial pressure of chlorine is reduced by 50%?

A) POCl₃ will be consumed as equilibrium is established.
B) POCl will be consumed as equilibrium is established.
C) Chlorine will be consumed as equilibrium is established.
D) The partial pressure of POCl will decrease while the partial pressure of Cl₂ increases as equilibrium is established.
E) The volume will have to decrease before equilibrium can be reestablished.

Question 43

The following reaction, in CCl₄ solvent, has been studied at 25°C. 2BrCl Br₂ + Cl₂
The equilibrium constant K_c is known to be 0.141. If the initial concentration of chlorine is 0.0300 M and of bromine monochloride is 0.0200 M, what is the equilibrium concentration of bromine?

A) 1.35 × 10^-3 M
B) 2.70 × 10^-3 M
C) 8.82 × 10^-3 M
D) 9.70 × 10^-2 M
E) none of the above

Question 44

A mixture 0.500 mole of carbon monoxide and 0.400 mole of bromine was placed into a rigid 1.00-L container and the system was allowed to come to equilibrium. The equilibrium concentration of COBr₂ was 0.233 M. What is the value of K_c for this reaction? CO(g) + Br₂(g) COBr₂(g)

A) 5.23
B) 1.22
C) 1.165
D) 0.858
E) 0.191

Question 45

At a certain temperature the reaction CO₂(g) + H₂(g) CO(g) + H₂O(g)
Has K_c = 2.50. If 2.00 mol of carbon dioxide and 1.5 mol of hydrogen are placed in a 5.00 L vessel and equilibrium is established, what will be the concentration of carbon monoxide?

A) 0.091 M
B) 0.191 M
C) 0.209 M
D) 0.913 M
E) 1.05 M

Question 46

Consider the reversible reaction: 2NO₂(g) N₂O₄(g) If the concentrations of both NO₂ and N₂O₄ are 0.016 mol L^-1, what is the value of Q_c?

A) 0.016
B) 0.50
C) 1.0
D) 2.0
E) 63

Question 47

The equilibrium constant K_c for the reaction A(g) + B(g) C(g)
Is 0.76 at 150°C. If 0.800 mol of A is added to 0.600 mol of B in a 1.00-L container at 150°C, what will be the equilibrium concentration of C?

A) 0.19 M
B) 0.29 M
C) 0.36 M
D) 0.41 M
E) 0.51 M

Question 48

Ammonium iodide dissociates reversibly to ammonia and hydrogen iodide. NH₄I(s) NH₃(g) + HI(g)
At 400°C, K_p = 0.215. Calculate the partial pressure of ammonia at equilibrium when a sufficient quantity of ammonium iodide is heated to 400°C.

A) 0.103 atm
B) 0.215 atm
C) 0.232 atm
D) 0.464 atm
E) 2.00 atm

Question 49

The reaction system POCl₃(g) POCl(g) + Cl₂(g)
Is at equilibrium. Which of the following statements describes the behavior of the system if POCl is added to the container?

A) The forward reaction will proceed to establish equilibrium.
B) The reverse reaction will proceed to establish equilibrium.
C) The partial pressures of POCl₃ and POCl will remain steady while the partial pressure of chlorine increases.
D) The partial pressure of chlorine remains steady while the partial pressures of POCl₃ and POCl increase.
E) The partial pressure of chlorine will increase while the partial pressure of POCl decreases.

Question 50

At 850°C, the equilibrium constant K_p for the reaction C(s) + CO₂(g) 2CO(g)
Has a value of 10.7. If the total pressure in the system at equilibrium is 1.000 atm, what is the partial pressure of carbon monoxide?

A) 0.362 atm
B) 0.489 atm
C) 0.667 atm
D) 0.915 atm
E) 0.921 atm

Question 51

Nitric oxide is formed in automobile exhaust when nitrogen and oxygen in air react at high temperatures. N₂(g) + O₂(g) 2NO(g)
The equilibrium constant K_p for the reaction is 0.0025 at 2127°C. If a container is charged with 8.00 atm of nitrogen and 5.00 atm of oxygen and the mixture is allowed to reach equilibrium, what will be the equilibrium partial pressure of nitrogen?

A) 0.16 atm
B) 0.31 atm
C) 3.1 atm
D) 7.7 atm
E) 7.8 atm

Question 52

At high temperatures, carbon reacts with O₂ to produce CO as follows: C(s) + O₂(g)
2CO(g).
When 0.350 mol of O₂ and excess carbon were placed in a 5.00-L container and heated, the equilibrium concentration of CO was found to be 0.060 M. What is the equilibrium constant, K_c, for this reaction?

A) 0.010
B) 0.072
C) 0.090
D) 0.17
E) 1.2

Question 53

The equilibrium constant, K_p , for the reaction CO(g) + H₂O(g) CO₂(g) + H₂(g)
At 986°C is 0.63. A rigid cylinder at that temperature contains 1.2 atm of carbon monoxide, 0.20 atm of water vapor, 0.30 atm of carbon dioxide, and 0.27 atm of hydrogen. Is the system at equilibrium?

A) Yes.
B) No, the forward reaction must proceed to establish equilibrium.
C) No, the reverse reaction must proceed to establish equilibrium.
D) Need to know the volume of the container before deciding.
E) Need to know the starting concentrations of all substances before deciding.

Question 54

Nitric oxide and bromine were allowed to react in a sealed container. When equilibrium was reached P_NO = 0.526 atm, = 1.59 atm, and P_NOBr = 7.68 atm. Calculate K_p for the reaction. 2NO(g) + Br₂(g) 2NOBr(g)

A) 7.45 × 10^-3
B) 0.109
C) 9.18
D) 91.8
E) 134

Question 55

Hydrogen iodide, HI, is formed in an equilibrium reaction when gaseous hydrogen and iodine gas are heated together. If 20.0 g of hydrogen and 20.0 g of iodine are heated, forming 10.0 g of hydrogen iodide, what mass of hydrogen remains unreacted?

A) 10.0 g hydrogen remains
B) 10.9 g hydrogen remains
C) 15.0 g hydrogen remains
D) 19.9 g hydrogen remains
E) Need to know the equilibrium constant in order to calculate the answer.

Question 56

SO₂ reacts with O₂ to produce SO₃. If 86.0 g of SO₂ is placed in a reaction vessel along with excess oxygen gas, how many moles of SO₂ remain when 50.0 g of SO₃ have been formed?

A) 0.56 mol
B) 0.62 mol
C) 0.72 mol
D) 0.78 mol
E) 1.34 mol

Question 57

A mixture of 0.600 mol of bromine and 1.600 mol of iodine is placed into a rigid 1.000-L container at 350°C. Br₂(g) + I₂(g) 2IBr(g)
When the mixture has come to equilibrium, the concentration of iodine monobromide is 1.190 M. What is the equilibrium constant for this reaction at 350°C?

A) 3.55 × 10^-3
B) 1.24
C) 1.47
D) 282
E) 325

Question 58

The equilibrium constant K_c for the reaction PCl₃(g) + Cl₂(g) PCl₅(g)
Is 49 at 230°C. If 0.70 mol of PCl₃ is added to 0.70 mol of Cl₂ in a 1.00-L reaction vessel at 230°C, what is the concentration of PCl₃ when equilibrium has been established?

A) 0.049 M
B) 0.11 M
C) 0.30 M
D) 0.59 M
E) 0.83 M

Question 59

At 25°C, the equilibrium constant K_c for the reaction 2A(aq) B(aq) + C(aq)
Is 65. If 2.50 mol of A is added to enough water to prepare 1.00 L of solution, what will the equilibrium concentration of A be?

A) 0.038 M
B) 0.14 M
C) 0.28 M
D) 1.18 M
E) 2.4 M

Question 60

Compounds A, B, and C react according to the following equation. 3A(g) + 2B(g) 2C(g)
At 100°C a mixture of these gases at equilibrium showed that [A] = 0.855 M, [B] = 1.23 M, and [C] = 1.75 M. What is the value of K_c for this reaction?

A) 0.309
B) 0.601
C) 1.66
D) 3.24
E) > 10

Question 61

Nitrogen dioxide can dissociate to nitric oxide and oxygen. 2NO₂(g) 2NO(g) + O₂(g) $\Delta$ H°_rxn = +114 kJ
Under which reaction conditions would you expect to produce the largest amount of oxygen?

A) high temperature, high pressure
B) low temperature, high pressure
C) high temperature, low pressure
D) low temperature, low pressure
E) none of the above, unless a catalyst is present

Question 62

Write the expressions for K_c and K_p for the reaction
PH₃BCl₃(s) PH₃(g) + BCl₃(g)

Question 63

The following reaction is at equilibrium in a sealed container. N₂(g) + 3H₂(g) 2NH₃(g) $\Delta$ H°_rxn < 0
Which, if any, of the following actions will increase the value of the equilibrium constant, K_c?

A) adding a catalyst
B) adding more N₂
C) increasing the pressure
D) lowering the temperature
E) none of the above

Question 64

The reaction system CS₂(g) + 4H₂(g) CH₄(g) + 2H₂S(g)
Is at equilibrium. Which of the following statements describes the behavior of the system if the partial pressure of carbon disulfide is reduced?

A) As equilibrium is reestablished, the partial pressure of carbon disulfide increases.
B) As equilibrium is reestablished, the partial pressure of hydrogen decreases.
C) As equilibrium is reestablished, the partial pressure of methane, CH₄, increases.
D) As equilibrium is reestablished, the partial pressures of hydrogen and hydrogen sulfide decrease.
E) As equilibrium is reestablished, all the partial pressures will increase.

Question 65

Methanol can be synthesized by combining carbon monoxide and hydrogen. CO(g) + 2H₂(g) CH₃OH(g)
A reaction vessel contains the three gases at equilibrium with a total pressure of 1.00 atm. What will happen to the partial pressure of hydrogen if enough argon is added to raise the total pressure to 1.4 atm?

A) The partial pressure of hydrogen will decrease.
B) The partial pressure of hydrogen will increase.
C) The partial pressure of hydrogen will be unchanged.
D) K_p needs to be known before a prediction can be made.
E) Both K_p and the temperature need to be known before a prediction can be made.

Question 66

Stearic acid, nature's most common fatty acid, dimerizes when dissolved in hexane: 2C₁₇H₃₅COOH (C₁₇H₃₅COOH)₂ $\Delta$ H°_rxn = -172 kJ
The equilibrium constant for this reaction at 28°C is 2900. Estimate the equilibrium constant at 38°C.

A) 4.7 × 10⁵
B) 2.6 × 10⁴
C) 1.9 × 10³
D) 3.2 × 10²
E) 18

Question 67

The reaction system CS₂(g) + 4H₂(g) CH₄(g) + 2H₂S(g)
Is at equilibrium. Which of the following statements describes the behavior of the system if the partial pressure of hydrogen is doubled?

A) As equilibrium is reestablished, the partial pressure of carbon disulfide increases.
B) As equilibrium is reestablished, the partial pressure of methane, CH₄, decreases.
C) As equilibrium is reestablished, the partial pressure of hydrogen decreases.
D) As equilibrium is reestablished, the partial pressure of hydrogen sulfide decreases.
E) As equilibrium is reestablished, all the partial pressures will decrease.

Question 68

The following reaction is at equilibrium at one atmosphere, in a closed container. NaOH(s) + CO₂(g) NaHCO₃(s)
Which, if any, of the following actions will decrease the total amount of CO₂ gas present at equilibrium?

A) adding N₂ gas to double the pressure
B) adding more solid NaOH
C) decreasing the volume of the container
D) removing half of the solid NaHCO₃
E) none of the above

Question 69

The following reaction is at equilibrium in a closed container. CuSO₄.5H₂O(s) CuSO₄(s) + 5H₂O(g)
Which, if any, of the following actions will lead to an increase in the pressure of H₂O present at equilibrium?

A) increasing the volume of the container
B) decreasing the volume of the container
C) adding a catalyst
D) removing some solid CuSO₄
E) none of the above

Question 70

Methanol can be synthesized by combining carbon monoxide and hydrogen. CO(g) + 2H₂(g) CH₃OH(g) $\Delta$ H°_rxn = -90.7 kJ
A reaction vessel contains these compounds at equilibrium. What effect will be seen when equilibrium is re-established after decreasing the temperature by 45°C?

A) All the partial pressures will decrease.
B) The partial pressure of methanol will decrease.
C) The partial pressures of hydrogen and methanol will decrease.
D) The partial pressure of hydrogen will increase.
E) The partial pressure of carbon monoxide will decrease.

Question 71

At 450°C, tert-butyl alcohol decomposes into water and isobutene. (CH₃)₃COH(g) (CH₃)₂CCH₂(g) + H₂O(g)
A reaction vessel contains these compounds at equilibrium. What will happen if the volume of the container is reduced by 50% at constant temperature?

A) The forward reaction will proceed to reestablish equilibrium.
B) The reverse reaction will proceed to reestablish equilibrium.
C) No change occurs.
D) The equilibrium constant will increase.
E) The equilibrium constant will decrease.

Question 72

Hydrogen sulfide can be formed in the following reaction: H₂(g) + S₂(g) H₂S(g) $\Delta$ H°_rxn = -92 kJ
The equilibrium constant K_p = 106 at 1023 K. Estimate the value of K_p at 1218 K.

A) 5.05
B) 18.8
C) 34.7
D) 88.9
E) 598

Question 73

Sodium hydrogen carbonate decomposes above 110°C to form sodium carbonate, water, and carbon dioxide. 2NaHCO₃(s) Na₂CO₃(s) + H₂O(g) + CO₂(g)
One thousand grams of sodium hydrogen carbonate are added to a reaction vessel, the temperature is increased to 200°C, and the system comes to equilibrium. What happens in this system if another 50 g of sodium carbonate are now added?

A) The partial pressure of carbon dioxide will increase.
B) The partial pressure of carbon dioxide will decrease.
C) The partial pressure of carbon dioxide will be unchanged.
D) The amounts of all products will be greater when equilibrium is reestablished.
E) None of the above conclusions is justified without knowing the equilibrium constant.

Question 74

Magnesium carbonate dissociates to magnesium oxide and carbon dioxide at elevated temperatures. MgCO₃(s) MgO(s) + CO₂(g)
A reaction vessel contains these compounds in equilibrium at 300°C. What will happen if the volume of the container is reduced by 25% at 300°C?

A) The partial pressure of carbon dioxide present at equilibrium will increase.
B) The partial pressure of carbon dioxide present at equilibrium will decrease.
C) The partial pressure of carbon dioxide at equilibrium will be unchanged.
D) The equilibrium constant will have to decrease to compensate for the decrease in volume.
E) More information is needed in order to make a valid judgment.

Question 75

The reaction of nitric oxide to form dinitrogen oxide and nitrogen dioxide is exothermic. 3NO(g) N₂O(g) + NO₂(g) + heat
What effect will be seen if the temperature of the system at equilibrium is raised by 25°C?

A) The partial pressure of NO will increase.
B) The partial pressure of NO will decrease.
C) The partial pressure of NO₂ will increase.
D) The partial pressures of NO and N₂O will increase.
E) All three partial pressures will increase.

Question 76

Hydrogen bromide will dissociate into hydrogen and bromine gases. 2HBr(g) H₂(g) + Br₂(g) $\Delta$ H°_rxn = 68 kJ
What effect will a temperature increase of 50°C have on this system at equilibrium?

A) The partial pressure of hydrogen bromide will increase.
B) The partial pressure of hydrogen will increase.
C) The partial pressure of hydrogen bromide and bromine will increase.
D) There will be no effect on the partial pressure of any of the gases.
E) Need to know the initial pressure, volume, and temperature before any of the above predictions can be made.

Question 77

The following reaction is at equilibrium at a pressure of 1 atm, in a closed container. NaOH(s) + CO₂(g) NaHCO₃(s) $\Delta$ H°_rxn < 0
Which, if any, of the following actions will decrease the concentration of CO₂ gas present at equilibrium?

A) adding N₂ gas to double the pressure
B) adding more solid NaOH
C) increasing the volume of the container
D) lowering the temperature
E) none of the above

Question 78

Magnesium hydroxide is used in several antacid formulations. When it is added to water it dissociates into magnesium and hydroxide ions. Mg(OH)₂(s) Mg²⁺(aq) + 2OH^-(aq)
The equilibrium constant at 25°C is 8.9 × 10^-12. One hundred grams of magnesium hydroxide is added to 1.00 L of water and equilibrium is established. What happens to the solution if another 10 grams of Mg(OH)₂ are now added to the mixture?

A) The hydroxide ion concentration will decrease.
B) The hydroxide ion concentration will increase.
C) The hydroxide ion concentration will be unchanged.
D) The solution will become supersaturated.
E) None of the above conclusions is justified without additional information.

Question 79

Ethane can be formed by reacting acetylene with hydrogen. C₂H₂(g) + 2H₂(g) C₂H₆(g) $\Delta$ H°_rxn = -311 kJ
Under which reaction conditions would you expect to have the greatest equilibrium yield of ethane?

A) high temperature, high pressure
B) low temperature, high pressure
C) high temperature, low pressure
D) low temperature, low pressure
E) none of the above, unless a catalyst is present

Question 80

A container was charged with hydrogen, nitrogen, and ammonia gases at 120°C and the system was allowed to reach equilibrium. What will happen if the volume of the container is increased at constant temperature? 3H₂(g) + N₂(g) 2NH₃(g)

A) There will be no effect.
B) More ammonia will be produced at the expense of hydrogen and nitrogen.
C) Hydrogen and nitrogen will be produced at the expense of ammonia.
D) The equilibrium constant will increase.
E) The equilibrium constant will decrease.