Chapter 13: Fundamental Equilibrium Concepts

Question 1

What is chemical equilibrium?

A) The reaction stops completely.
B) The concentration of reactants becomes zero.
C) The rate of the forward reaction is equal to the rate of the reverse reaction.
D) The reaction only proceeds in the forward direction.

Answer 1

C) The rate of the forward reaction is equal to the rate of the reverse reaction.

Question 2

Which of the following is the correct equilibrium expression for the reaction: 3O₂(g) ⇌ 2O₃(g)?
A) Qc = [O₂]³ / [O₃]²
B) Qc = [O₃]² / [O₂]³
C) Qc = [O₂]² / [O₃]³
D) Qc = [O₃]³ / [O₂]²

Answer 2

B) Qc = [O₃]² / [O₂]³

Question 3

The reaction quotient (Q) can be solved for which phases?
A) Only gases
B) Only aqueous solutions
C) Both aqueous and gas phases
D) Solids, liquids, gases, and aqueous phases

Answer 3

C) Both aqueous and gas phases

Question 4

For which type of reaction can Qp be used?
A) Only for gaseous reactions
B) For all reactions
C) Only for solid reactions
D) For reactions involving solids and liquids

Answer 4

A) Only for gaseous reactions

Question 5

Which of the following is true regarding the reaction quotient (Q)?
A) Q can be solved for solids and liquids.
B) Q is only applicable to heterogeneous equilibria.
C) Q cannot be solved for solids or liquids since they do not have a concentration.
D) Q is independent of concentration and pressure.

Answer 5

C) Q cannot be solved for solids or liquids since they do not have a concentration.

Question 6

Which of the following is an example of a homogeneous equilibrium?
A) (A)g + B(g) ⇌ C(g)
B) A(s) + B(l) + C(g) ⇌ D(aq)
C) H₂O(l) ⇌ H₂O(g)
D) NaCl(s) ⇌ Na⁺(aq) + Cl⁻(aq)

Answer 6

A) (A)g + B(g) ⇌ C(g)

Question 7

Which of the following is an example of a heterogeneous equilibrium?
A) 2NO₂(g) ⇌ N₂O₄(g)
B) N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
C) A(s) + B(l) + C(g) ⇌ D(aq)
D) CH₄(g) + 2O₂(g) ⇌ CO₂(g) + 2H₂O(g)

Answer 7

C) A(s) + B(l) + C(g) ⇌ D(aq)

Question 8

What does it mean if K > 1?
A) The concentration of reactants is greater than the concentration of products.
B) The concentration of products is greater than the concentration of reactants.
C) The system is not at equilibrium.
D) The reaction stops completely.

Answer 8

B) The concentration of products is greater than the concentration of reactants.

Question 9

What does it mean if K < 1?
A) The concentration of reactants is greater than the concentration of products.
B) The concentration of products is greater than the concentration of reactants.
C) The system is at equilibrium.
D) The reaction will shift toward the products.

Answer 9

A) The concentration of reactants is greater than the concentration of products.

Question 10

If Q > K, what does this imply about the reaction?
A) Products are greater than they should be, and the reaction will shift left.
B) Reactants are greater than they should be, and the reaction will shift right.
C) The reaction is at equilibrium.
D) The reaction will not proceed.

Answer 10

A) Products are greater than they should be, and the reaction will shift left.

Question 11

If Q < K, what does this imply about the reaction?
A) Products are greater than they should be, and the reaction will shift left.
B) Reactants are greater than they should be, and the reaction will shift right.
C) The reaction is at equilibrium.
D) The reaction will not proceed.

Answer 11

B) Reactants are greater than they should be, and the reaction will shift right.

Question 12

What is the value of the initial reaction quotient (Qc) for the reaction 2NO₂(g) ⇌ N₂O₄(g) when 0.10 mol of NO₂ is added to a 1.0 L flask at 25°C?
A) 0
B) 1.6 × 10²
C) 0.42
D) 1.0

Answer 12

A) 0

Qc= 0/(0.10)^2=0/0.01=0

Since Qc = 0, the correct answer is A) 0 because there is no N₂O₄ initially to contribute to the numerator.

Question 13

For the reaction CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g), if Qc = 0.040 and Kc = 0.64, what does this indicate?

A) The reaction is product-favored.
B) The reaction is reactant-favored.
C) The reaction is at equilibrium.
D) The reaction will not proceed.

Answer 13

A) The reaction is product-favored.

Qc<Kc

Question 14

For the reaction PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), if Qc = 5.0 and Kc = 0.50, what does this indicate?

A) The reaction is product-favored.
B) The reaction is reactant-favored.
C) The reaction is at equilibrium.
D) The reaction will not proceed.

Answer 14

B) The reaction is reactant-favored.

Qc>Kc

Question 15

For the reaction SO₂(g) + O₂(g) ⇌ SO₃(g), if Qc = 0.25 and Kc = 1.8, what does this indicate?

A) The reaction is product-favored.
B) The reaction is reactant-favored.
C) The reaction is at equilibrium.
D) The reaction will not proceed.

Answer 15

A) The reaction is product-favored.

Qc < Kc

Question 16

What is the correct equation for Kp in terms of Kc?
A) Kp = Kc(RT)^Δn
B) Kp = Kc/RT
C) Kp = Kc(Δn)^RT
D) Kp = Kc(RT)

Answer 16

A) Kp = Kc(RT)^Δn

Question 17

For the reaction CS₂(g) + 4H₂(g) ⇌ CH₄(g) + 2H₂S(g), if Kc = 0.28 at 900°C, what is Δn in the equation Kp = Kc(RT)^Δn?
A) -2
B) 2
C) 0
D) 1

Answer 17

A) -2

[(1)+(2)]-[(1)+(4)] = -2

Question 18

iven the equilibrium reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), calculate Kp if Kc = 4.2 at 700°C. (R = 0.0821 L·atm/(mol·K))
A) 150
B) 38
C) 0.52
D) 4900

Answer 18

C) 0.52

(4.2)[(0.0821973)]^-1 = 0.52

Question 19

According to Le Chatelier’s Principle, what happens to the equilibrium position when additional reactant is added to a reaction at equilibrium?

A) The reaction shifts right to form more products.
B) The reaction shifts left to form more reactants.
C) The reaction does not shift at all.
D) The reaction stops completely.

Answer 19

A) The reaction shifts right to form more products.

Question 20

How does a decrease in volume affect an equilibrium system involving gases?

A) The reaction shifts to the side with more moles of gas.
B) The reaction shifts to the side with fewer moles of gas.
C) The reaction stops.
D) The reaction shifts in the direction of the reactants.

Answer 20

B) The reaction shifts to the side with fewer moles of gas.

Question 21

For an exothermic reaction, how is heat treated in Le Chatelier’s Principle?

A) Heat is treated as a reactant.
B) Heat is treated as a product.
C) Heat is ignored when considering equilibrium shifts.
D) Heat only affects pressure, not equilibrium.

Answer 21

B) Heat is treated as a product.

Question 22

If a reaction is endothermic and the temperature is increased, what happens to equilibrium?

A) The reaction shifts to the left, toward reactants.
B) The reaction shifts to the right, toward products.
C) The reaction stops.
D) The reaction remains unchanged.

Answer 22

B) The reaction shifts to the right, toward products.

Question 23

What is the effect of adding a catalyst to a reaction at equilibrium?
A) The reaction shifts to the right.
B) The reaction shifts to the left.
C) The equilibrium position remains unchanged, but the reaction reaches equilibrium faster.
D) The reaction completely stops.

Answer 23

C) The equilibrium position remains unchanged, but the reaction reaches equilibrium faster.

Question 24

In an equilibrium calculation using an ICE table, what does the ‘C’ row represent?

A) The concentration at the start of the reaction.
B) The amount of reactant or product added to the system.
C) The change in concentration as the reaction shifts to equilibrium.
D) The final equilibrium concentrations of all species.

Answer 24

C) The change in concentration as the reaction shifts to equilibrium.

Question 25

When can the 5% approximation be used in equilibrium calculations? A) When 𝐾>1000 B) When K<1000 times less than the initial concentration. C) When the reaction is exothermic. D) When the reaction is endothermic.

Answer 25

B) When K<1000 times less than the initial concentration.

Question 26

The relationship between Gibbs Free Energy and equilibrium constant is given by which equation? A) ΔG=ΔH−TΔS B) K=e ^−ΔG/RT C) P=kC D) ΔG=−ΔH+TΔS

Answer 26

B) K=e ^−ΔG/RT

Question 27

Which of the following equilibrium systems will shift right when the pressure is decreased? A) 𝑁2 (g) + 3H2 (g) ⇌ 2NH3(g) B) PCl5 (g) ⇌ PCl3(g) + Cl2(g) C) 2SO3(g) ⇌ 2SO2(g) + O2(g) D) None of the above

Answer 27

C) 2SO3(g) ⇌ 2SO2(g) + O2(g) Explanation: When pressure decreases, the reaction shifts toward the side with more moles of gas.

Question 28

If K>1, what does that indicate about the reaction? A) Reactants are more abundant than products. B) Products are more abundant than reactants. C) The reaction is non-spontaneous. D) The system is always at equilibrium.

Answer 28

B) Products are more abundant than reactants.

Question 29

In an ICE table, what does the "E" row represent? A) The initial concentrations before the reaction starts. B) The amount of reactants and products gained or lost. C) The equilibrium concentrations of all species. D) The rate of the reaction at equilibrium.

Answer 29

C) The equilibrium concentrations of all species.

Question 30

What is the equilibrium expression for the reaction: 2NO2(g) ⇌ 2NO(g) +O2(g) a.) K = ([NO]^2[O2]/[NO2]^2) b.) K = ([NO2]^2/[NO]^2[O2]) c.) K = ([NO][O2]2/[NO2]^2) d.) K = ([NO2]/[NO][O2])

Answer 30

a.) K = ([NO]^2[O2]/[NO2]^2)

Question 31

If the forward reaction is exothermic, what happens when temperature increases? A) The reaction shifts to the right. B) The reaction shifts to the left. C) The reaction does not shift. D) The reaction speeds up but remains at equilibrium.

Answer 31

B) The reaction shifts to the left.

Question 32

For an endothermic reaction, how does decreasing temperature affect equilibrium? A) The reaction shifts toward reactants. B) The reaction shifts toward products. C) The reaction stops. D) There is no change in equilibrium.

Answer 32

A) The reaction shifts toward reactants.

Question 33

If a reaction is exothermic, what is the sign of ΔH? A) Positive B) Negative C) Zero D) It depends on the equilibrium constant

Answer 33

B) Negative

Question 34

Which of the following is TRUE about an ICE table? A) The "C" row represents initial concentrations. B) The "E" row always contains only positive numbers. C) The "I" row contains given initial concentrations. D) The "E" row always contains the equilibrium constant 𝐾.

Answer 34

C) The "I" row contains given initial concentrations.

Question 35

What happens when a system at equilibrium is subjected to a stress? A) The equilibrium constant changes. B) The system shifts to counteract the stress. C) The reaction stops permanently. D) The forward reaction stops while the reverse continues.

Answer 35

B) The system shifts to counteract the stress.

Question 36

CE Table Example For the reaction: H2(g)+I2(g) ⇌ 2HI(g) A reaction vessel initially contains 1.50 M H₂ and 1.50 M I₂ with 0.00 M HI. At equilibrium, the concentration of HI is 1.94 M. What is the equilibrium concentration of H₂? A) 0.53 M B) 0.94 M C) 1.47 M D) 0.26 M

Answer 36

A) 0.53 M 2x=1.94 𝑥=0.97

Question 37

When a system is at dynamic equilibrium: a.) no reactions are occurring b.) a reaction is occurring in only one direction c.) the rates of the forward and reverse reactions are equal d.) all of the reactants have been converted to products

Answer 37

c.) the rates of the forward and reverse reactions are equal

Question 38

Which of the following statements is always true for a reaction at equilibrium? I. The rate of the forward reaction and reverse reactions are equal. II. The concentrations of the reactants and the products remain constant. III. The amount of reactants is equal to the amount of products. a.) I and II b.) I and III c.) II and III d.) I, II, and III e.) none of the above

Answer 38

a.) I and II

Question 39

For a particular reaction K=98000. What can be said about this reaction? a.) There are many more products than reactants in the equilibrium mixture. b.) There are many more reactants than products in the equilibrium mixture. c.) There are roughly equal amounts of reactants and products in the equilibrium mixture. d.) The reaction has not yet reached equilibrium because K does not equal 1.

Answer 39

a.) There are many more products than reactants in the equilibrium mixture.

Question 40

For the reaction below, Qp = 600. What must happen for the reaction to reach equilibrium? 2A(g) + B(s) ⇌ 2C(s) + D(g) Kp=8210 a.) The reaction needs to shift in the forward direction. b.) The reaction needs to shift in the reverse direction. c.) The reaction is already at equilibrium and no shift needs to take place. D. There is not enough information to determine how the reaction will reach equilibrium.

Answer 40

a.) The reaction needs to shift in the forward direction. K>Q indicates that the reaction will shift in the forward direction.

Question 41

If the equilibrium constant of a given reaction is 3.60, what is the equilibrium constant of its reverse reaction?

Answer 41

0.278 (1/3.60)

Question 42

Consider the following reactions: A ⇌ B, K₁=4.59 A ⇌ C, K₂=2.00 What is K for the reaction C ⇌ B

Answer 42

1/2 = 0.5 0.5 * 4.59 = 2.30

Question 43

The Kp for the reaction A (g) ⇌ 2 B (g) is 0.0600. What is Kp for the reaction 4 B (g) ⇌ 2 A (g)?

Answer 43

1/0.0600 for the flip 16.6*16.6 since it doubled (need to use ^2) 276.7

Question 44

Consider the reaction: 2 HI (g) ⇌ H₂ (g) + I₂ (g) At equilibrium, the partial pressure of HI is 1.9 atm and the partial pressures of H₂ and I₂ are 7.9 and 2.3 respectively. What is Kp for this equilibrium?

Answer 44

5.03 (2.3*7.9)/1.9^2

Question 45

Consider the reaction: N₂ (g) + 3 Br₂ (g) ⇌ 2 NBr₃ (g) At equilibrium, the concentrations of N₂ and Br₂ are 0.34 M and 0.70 M respectively, and the concentration of NBr₃ is 0.090 M. What is Kc for this equilibrium?

Answer 45

0.069

Question 46

At 355 K, ∆G = -5.7 kJ/mol for the reaction A (g) → 2 B (g). If the partial pressures of A and B are 5.61 atm and 0.110 atm respectively, what is the standard free energy for this reaction at this temperature?

Answer 46

ΔG=ΔG ∘+RTlnQ Q=(P^2B)/(PA) or Q=(0.110^2)/(5.61) =0.00216 ΔG ∘ =(−5.7)−(0.008314)(355)ln(0.00216) =12.4 kJ/mol

Question 47

For the reaction 2 A (g) → B (g), Kp = 0.00247 at 298 K. When ∆G = 8.35 kJ/mol, what is the partial pressure of B when the partial pressure of A is 2.00 atm for this reaction at 298 K.

Answer 47

ΔG=RTIn(Q/K) 0.287 atm

Question 48

Consider the reaction below: 2 CO(g) + O₂(g) ⇌ 2 CO₂(g) If Kc is 2.24 × 10²² at 1298.0 °C, calculate Kp at the same temperature. Note Kc is sometimes called K. (R = 0.08314 L･bar/mol･K.)

Answer 48

1.71*10^20

Question 49

Consider the following acidic equilibrium: H₂CO₃(aq) + H₂O(l) ⇌ HCO₃⁻(aq) + H₃O⁺(aq). If you add NaHCO₃ to this solution, which of the following will occur? a.) The reaction quotient will decrease. b.) The reaction will shift in the reverse direction. c.) The equilibrium constant will increase. d.) No changes to the equilibrium positions will take place.

Answer 49

b.) The reaction will shift in the reverse direction.

Question 50

Consider the following chemical reaction at equilibrium: 2NO₂(g) ⇌ N₂O₄(g) If the container's volume is increased by a factor of 2, in which direction will the equilibrium shift? a.) reactants b.) product c.) neither the reactants nor the product

Answer 50

a.) reactants

Question 51

onsider the following chemical reaction at equilibrium: 2NO₂(g) ⇌ N₂O₄(g) ∆H°rxn < 0 If the temperature is increased by 20 K while the pressure is kept constant, how will Keq for the reaction change? a.) increase b.) decrease c.) stay the same

Answer 51

b.) decrease Because ΔH∘rxn<0,Keq decreases with increasing temperature. The reaction is exothermic, so increasing the temperature favors the reactant over the product.

Question 52

Consider the reaction below. Which of the following would increase the partial pressure of A at equilibrium? A (g) + B (g) ⇌ C (g) ΔH > 0 a.) adding B c.) removing C c.) increasing temperature d.) decreasing temperature

Answer 52

d.) decreasing temperature A positive ΔH indicates that this is an endothermic reaction with energy being required for the forward reaction to occur. Decreasing the temperature would shift the reaction to the left to create more reactants to reach equilibrium.

Question 53

Which of the following statements best described Le Chatelier's Principle? a.) Reactions can never really reach equilibrium. b.) A reaction which is at equilibrium will always try to stay at equilibrium. c.) A reaction which is at equilibrium, when disturbed, will react appropriately to reestablish equilibrium. d.) All reactants will eventually run to equilibrium.

Answer 53

c.) A reaction which is at equilibrium, when disturbed, will react appropriately to reestablish equilibrium.

Question 54

Consider the following chemical reaction at equilibrium: HF(aq) + H₂O(l) ⇌ H₃O⁺(aq) + F⁻(aq) If one drop of aqueous hydrochloric acid (HCl) is added, in which direction will the equilibrium (Q) shift? a.) reactants b.) products c.) neither the reactants nor the products

Answer 54

a.) reactants Hydrochloric acid is a strong acid, and dissociates to form H⁺ ions that react with the strongest base present in solution, fluoride to form hydrofluoric acid . This causes Q to be greater than and the equilibrium shifts towards reactants to Keq decrease Q to equal Keq.

Question 55

Consider the following reaction at equilibrium: 2NO₂(g) ⇌ N₂O₄(g) The ∆H° for this reaction is < 0. If the volume of the container is decreased by ½ while the temperature is kept constant, in which direction will the equilibrium shift? a.) reactants b.) products c.) no change

Answer 55

b.) products

Question 56

When NO₂ dimerizes (two molecules join together to form a 'dimer') into N₂O₄, an equilibrium is reached and in the process this reaction produces heat. If you increase the temperature of the chamber in which both NO₂ and N₂O₄ reside, you would observe a.) an increase in NO2 b.) an increase in N2O4 c.) no change in concentration d.) a decrease in the reaction rate.

Answer 56

a.) an increase in NO2

Question 57

Consider the reaction: 2 A (g) + B (s) ⇌ 2 C (s) + D (g) To increase the partial pressure of D at equilibrium, you could a.) add B b.) remove C c.) add A d.) add Ar(g)

Answer 57

c.) add A not add more B since it's a solid

Question 58

If a reaction favors products over reactants more as heat is added, that reaction is: a.) exothermic b.) endothermic c.) isobaric d.) isochoric

Answer 58

b.) endothermic

Question 59

A one-mole sample of NOBr was placed in a 10 L container at 25 °C, and the following reaction was allowed to come to equilibrium. 2 NOBr(g) ⇌ 2 NO(g) + Br₂(g) The equilibrium concentrations were found to be [NOBr] = 0.0838 M, [NO] = 0.0162 M and [Br₂] = 0.00810 M. Calculate the equilibrium constant, Kc, for the reaction.

Answer 59

3.03*10^-4

Question 60

Which of the following is always true for an equilibrium? a.) ΔS = 0 b.) ΔH = 0 c.) ΔG = 0 d.) T = 298 K e.) K = 0

Answer 60

c.) ΔG = 0

Question 61

A sample of PCl₅ was placed in a container and the following reaction was allowed to come to equilibrium. PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) The equilibrium concentrations were found to be [PCl₅] = 4.55 M and [PCl₃] = [Cl₂] = 0.437 M. Calculate Kc for the reaction.

Answer 61

0.0420

Question 62

Which of the following is true for a reaction when K is much less than one? a.) ΔG∘ = K b.) ΔG∘ = large negative number c.) ΔG∘ = large positive number d.) ΔG∘ = small negative number e.) ΔG∘ = small positive number

Answer 62

c.) ΔG∘ = large positive number

Question 63

At high temperatures, bromine molecules can dissociate into bromine atoms. For the reaction Br₂(g) ⇌ 2 Br･(g) Kp = 2.48 × 10⁻³ at 1650 °C. A 5.00 L vessel at 1650 °C is filled with Br₂(g) at an initial pressure of 8.00 atm and allowed to come to equilibrium. What will be the pressure (in atm) of Br･(g) at equilibrium?

Answer 63

Use ICE table: R I C E Br₂(g) 8.00 -x 8.00 - x Br·(g) 0.00 +2x 2x 2.48*10^-3 = (2x^2)/(8.00-x) 4x^2= +0.00248x−0.01984=0 plug into quadratic formula x=0.141 atm

Question 64

At high temperatures, iodine molecules can dissociate into iodine atoms. For the reaction I₂(g) ⇌ 2 I･(g) Kc = 1.27 × 10⁻⁴ at 900 °C. A 90.5 g sample of I₂ is placed in a 1.00 L vessel and heated to 900 °C. What will be the molar concentration of iodine atoms, [I･], in the vessel when the system comes to equilibrium?

Answer 64

Convert I2 to moles using molar mass: 90.5g/253.8 = .3466 Concentration: 0.3566/1.00 = 0.3566 Use ICE table: R I C E I₂(g) 8.00 -x 8.00 - x I·(g) 0.00 +2x 2x (2x)^2/(0.3566-x) = 1.27*10^-4 0.00670M

Question 65

For the reaction 2 SO₃(g) ⇌ 2 SO₂(g) + O₂(g) Kp = 2.62 × 10⁻⁶ at 400 °C. A 1.50 L vessel at 400 °C is filled with SO₃(g) at an initial pressure of 3.00 atm and allowed to come to equilibrium. What will be the pressure (in atm) of O₂(g) at equilibrium?

Answer 65

R I C E SO3(g) 3.00 -2x 3.00 - x SO2·(g) 0.00 +2x 2x O2(g) 0.00 +x x 2.62*10^-6=(2x)^2*x/(3.00-2x)^2 0.0179

Question 66

Determine the temperature of a reaction if K = 1.20 x 10⁻⁶ when ∆G° = +15.50 kJ/mol.

Answer 66

T=− ΔG/ RlnK 15.50/0.08314 In 1.20*10-6 136.75 K ​

Question 67

For the reaction below, Kc = 1.10 × 10⁻⁴. Note Kc is sometimes called K. What is the equilibrium concentration of C if the reaction begins with 0.200 M A and 0.550 M B? 2 A (aq) + B (aq) ⇌ C (aq)

Answer 67

2.42*10^-6 M

Question 68

Consider the reaction: ICl(g) + Cl₂(g) → ICl₃(s). The ∆G° of the reaction is -17.09 kJ/mol. Calculate the Keq for the reaction at 298.0 K.

Answer 68

Keq= 990 Keq = e^-ΔG/RT

Question 69

Determine the equilibrium constant for a reaction at 200.0 K if ∆G° =-12.50 kJ/mol. (R = 8.314 J/mol ･ K)

Answer 69

Keq = 1840