The Reaction Quotient

Consider this equilibrium reaction at 400 K. 

Br₂ (g) + Cl₂ (g) ⇌ 2BrCl (g)        K_c = 7.0 

If the composition of the reaction mixture at 400 K is [BrCl] = 0.00415 M, [Br₂] = 0.00366 M, and [Cl₂] = 0.000672 M, what is the reaction quotient, Q? 

How is the reaction quotient related to the equilibrium constant, K_c, for this reaction? 

           (i) Q < K 

           (ii) Q > K

           (iii) Q = K

2NO (g) + 2H₂ (g) → N₂ (g) + 2H₂O (g) 

At the temperature the engineer picks, the equilibrium constant K_p for this reaction is 0.052. 

The engineer charges ("fills") four reaction vessels with nitrogen monoxide and hydrogen, and lets the reaction begin. He then measures the composition of the mixture inside each vessel from time to time. His first set of measurements are shown in the table below. 

Predict the changes in the compositions the engineer should expect next time he measures the compositions.

What is the name of Q_c?

a. Reversibility expression

b. Reaction expression

c. Mass action

d. Equilibrium expression

e. Reaction quotient 

For the reaction 2A(g) ⇌ B(g), the equilibrium constant is K_p = 0.76. A reaction mixture initially contains 4.0 atm of gas (P_A = 2.0 atm and P_B = 2.0 atm). 

You may want to reference. Section 15.7 while completing this problem. 

Which statement is true of the reaction mixture? 

(a) The reaction mixture will proceed toward products. 

(b) The reaction mixture is at equilibrium. 

(c) The reaction mixture will proceed toward reactants 

(d) It is not possible to determine from the information given the future direction of the reaction mixture.

Predict and calculate the effect of concentration changes on an equilibrium system. 

Some SbCl₅ is allowed to dissociate into SbCl₃, and Cl₂ at 521 K. At equilibrium, [SbCl₅] = 0.163 M, and [SbCl₃] = [Cl₂] = 6.39 x 10^-2 M. Additional SbCl₅ is added so that [SbCl₅]_new = 0.287 M and the system is allowed to once again reach equilibrium. 

SbCl₅ (g) ⇌ SbCl₃ (g) + Cl₂ (g) K = 2.50 x 10^-2 at 521 K 

(a) In which direction will the reaction proceed to reach equilibrium? 

(b) What are the new concentrations of reactants and products after the system reaches equilibrium? 

The equilibrium constant for the following reaction is 0.16 M ^0.5 at 3000 K: 

CO₂ (g) <-> CO (g) + 0.5O₂(g) 

Determine Q_c if the following amounts (in moles) of each component is placed in a 3.00 L container. 

CO₂ 0.790 

CO 0.410 

O₂ 0.580 

Give answer to 3 decimal places.

The value of K_c for the reaction: 

2NO₂ (g) ⇌ N₂O₄(g) 

is 6.9 at 447 K. Determine the reaction quotient for a mixture of the two gases in which [NO  ₂] = 0.0311 M and [N₂O₄] = 0.00931 M.

Is a mixture of 0.0205 mol NO2(g) and 0.750 mol N2O4(g) and 0.750 mol N2O4(g) in a 5.25 - L flask at 25 ° C at equilibrium ? If not, in which direction will the reaction proceed - toward products or reactants?
N2O4(g)⇌ 2NO2(g) K_C = 4.61x10^-3 at 25 °C
a. The reaction will proceed to the right, toward products
b. The reaction will proceed to the left, toward reactants.
c. The mixture is at equilibrium.

Will a precipitate form if the metal ion concentration in a solution of M(CIO₂)₃ is 0.0246 M and the concentration of CIO₂ is 0.0148 M? Ksp for M(ClO₂)₃ = 6.25x10^-8 

Which of the following substances has the higher molar entropy (assume that each is in the gas phase)? 

The water-gas shift reaction plays a central role in the chemical methods for obtaining cleaner fuels from coal:

CO(g) + H2O(g) ⇌ CO2(g) + H2(g)

At a given temperature,Kp= 2.7. If 0.13 mol of CO, 0.56 mol of H2O, 0.62 mol of CO2, and 0.43 mol of H2 are put in a 2.0-L flask, in which direction does the reaction proceed ?

At 100°C, Kp = 60.6 for the reaction

2NOBr(g) ⇌ 2NO(g) + Br2(g)

In a given experiment, 0.10 atm of each component is placed in a container. Is the system at equilibrium? If not, in which direction will the reaction proceed?

At 425°C,Kp = 4.18× 10⁹ for the reaction

2HBr(g) ⇌ H2(g) + Br2(g)

In one experiment, 0.20 atm of HBr(g), 0.010 atm of H2(g) and 0.010 atm of Br2(g) are introduced into a container. Is the reaction at equilibrium? If not, in which direction will it proceed?

The following molecular scenes depict the aqueous reaction 2D ⇌ E, with D red and E blue. Each sphere represents 0.0100 mol, but the volume in scene A is 1.00 L, whereas in scenes B and C, it is 0.500 L.

(a) If the reaction in scene A is at equilibrium, calculate Kc

(b) Are the reactions in scenes B and C at equilibrium? Which if either, is not, and in which direction will it proceed?

When the numerical value of Q is less than K, in which direction does the reaction proceed to reach equilibrium? Explain.

The interhalogen ClF3 is prepared in a two-step fluorination of chlorine gas:

Cl2(g) + F2(g) ⇌ ClF(g)

ClF(g) + F2(g) ⇌ C1F3(g)

(a) Balance each step and write the overall equation.

(b) Show that the overall Qc equals the product of the Qc’s for the individual steps.

Write Qc for each of the following:

(a) Hydrogen chloride gas reacts with oxygen gas to produce chlorine gas and water vapor.

(b) Solid diarsenic trioxide reacts with fluorine gas to produce liquid arsenic pentafluoride and oxygen gas.

(c) Gaseous sulfur tetrafluoride reacts with liquid water to produce gaseous sulfur dioxide and hydrogen fluoride gas.

(d) Solid molybdenum(VI) oxide reacts with gaseous xenon di-fluoride to form liquid molybdenum(VI) fluoride, xenon gas, and oxygen gas.

Balance each of the following examples of heterogeneous equilibria and write its reaction quotient,Qc:

(a) H2O(l)+ SO3(g) ⇌H2SO4(aq)

(b) KNO3(s) ⇌ KNO2(s)+ O2(g)

(c) S8(s) + F2(g) ⇌ SF6(g)

Balance each of the following examples of heterogeneous equilibria and write its reaction quotient,Qc:

(a) Na2O2(s) + CO2(g) ⇌ Na2CO3(s) + O2(g)

(b) H2O(l) ⇌ H2O(g)

(c) NH4Cl(s) ⇌ NH3(g)+ HCl(g)

Balance each reaction and write its reaction quotient,Qc:

(a) C2H6(g)+ O2(g)⇌ CO2(g) + H2O(g)

(b) CH4(g) + F2(g) ⇌ CF4(g) + HF(g)

(c) SO3(g) ⇌ SO2(g) + O2(g)

Balance each reaction and write its reaction quotient,Qc:

(a) NO(g)+ O2(g) ⇌ N2O3(g)

(b) SF6(g)+ SO3(g) ⇌ SO2F2(g)

(c) SClF5(g) + H 2(g) ⇌ S2F10(g) + HCl(g)

Does Q for the formation of 1 mol of NH3 from H2 and N2 differ from Q for the formation of NH3 from H2 and 1 mol of N2? Explain and give the relationship between the two Q’s.

Does Q for the formation of 1 mol of NO from its elements differ from Q for the decomposition of 1 mol of NO to its elements? Explain and give the relationship between the two Q’s.

Balance the equation and write the reaction quotient expression. 

U(s) + F₂(g) ⇌ UF₆(g)

Balance the equation and write the reaction-quotient expression, Qc.

U (s) + F₂ (g) ⇌ UF₆ (g)

Qc=    ?/?

The diagram shows the free energy change of the reaction A(g) + B(g) ⇌ C(g).

The reaction progress starts on the left with pure reactants, A and B  each at 1 atm and moves to pure product, C, also at 1 atm on the right. Place the statements in the appropriate place on the diagram.

spontaneous
nonspontaneous
Q< K
Q> K
Q= K.

At 850 K the equilibrium constant for the following reaction is K _c = 15.

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
 

If we mix the following concentrations of the three gases, predict in which direction the reaction will proceed toward equilibrium: Left, Right, or No Reaction.

a. [SO₂] = 0.60 M, [O₂] = 0.70 M, [SO₃] = 0.16 M

b. [SO₂] = 0.20 M, [O₂] = 0.60 M, [SO₃] = 0.60 M

c. [SO₂] = 0.10 M, [O₂] = 0.20 M, [SO₃] = 0.40 M

Consider the reaction

Mg(s) + Fe²⁺(aq) → Mg²⁺(aq) + Fe(s) at 75°C

where [Fe²⁺] = 2.90M and [Mg ²⁺] = 0.310M

a. What is the value for the reaction quotient, Q, for the cell?

b. What is the value for the temperature, T, in kelvins?

At 850 K the equilibrium constant for the following reaction is Kc = 15.

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)

If we mix the following concentrations of the three gases, predict in which direction the net reaction will proceed toward equilibrium.

[SO₂] = 0.20 M
[O₂] = 0.60 M
[SO₃] = 0.60 M

[SO₂] = 0.14 M
[O₂] = 0.10 M
[SO₃] = 0.40 M

[SO₂] = 0.90 M
[O₂] = 0.50 M
[SO₃] = 0.10 M

What is the value of Q when the SrCrO ₄ solution contains 2.00 × 10⁻² M Sr ²⁺ and 1.50 × 10⁻³M CrO₄²⁻?

Calculate the value of Q.

In which direction will the net reaction proceed

X(g) + Y(g) ⇌ Z(g)          K_p = 1.00 at 300 K

for the set of initial condition?

 [X] = [Y] = [Z] = 1.0 M 

a) net reaction goes to the left

b) net reaction goes to the right

c) reaction is at equilibrium

Consider this system at equilibrium.

A(aq) ⇌ B(aq)        ΔH = +550 kJ/mol

What can be said about Q and K immediately after an increase in temperature?

A) Q > K because Q increased

B) Q > K because K decreased

C) Q < K because Q decreased

D) Q < K because K increased

E) Q = K because neither changed

How will the system respond to a temperature increase?

A) shift left

B) shift right

C) no change

Consider this system at equilibrium.

A(aq) ⇌ B(aq)        ΔH = -750 kJ/mol

What can be said about Q and K immediately after an increase in temperature?

A) Q > K because Q increased

B) Q > K because K decreased

C) Q < K because Q decreased

D) Q < K because K increased

E) Q = K because neither changed

How will the system respond to a temperature increase?

A) shift left

B) shift right

C) no change

At 500^oC, the K_p for the below reaction is 1.45 x10 ^-5. When 75 atm N₂, 35 atm H₂, and 5 atm of NH₃ are added to a container and heated to 500 ^oC, in which direction does the reaction proceed?

N₂ (g) + 3 H₂ (g) ⇌ 2 NH₃ (g)

A. The reaction proceeds to the right towards products until  Q_p=K_p

B. The reaction proceeds to the left towards reactants until  Q_p=K_p

C. The reaction proceeds to the right towards products until  Qp>K_p

D. The reaction proceeds to the left towards reactants until  Qp<K_p

Which of the following statements is TRUE?

A) If Q < K, it means the reverse reaction will proceed to form more reactants.

B) If Q > K, it means the forward reaction will proceed to form more products.

C) If Q = K, it means the reaction is at equilibrium.

D) All of the above are true.

E) None of the above are true.

Consider the following general reaction:

2 B₄A₄ (l) + 2 C₂ (g) → 4 A₂C (g) + 4 B₂ (g),           K _c =  0.0596

If you have a reaction mixture that contains 0.725 M concentration of each of these substances, in which direction will the reaction proceed?

A. Q = K; the reaction mixture is at equilibrium

B. Q < K; the reaction will shift towards the reactants

C. Q > K; the reaction will shift towards the products

D. Q > K; the reaction will shift towards the reactants

E. Q < K; the reaction will shift towards the products.

Consider the hypothetical reaction below
3 A (g) + B (g) ↔ 2 C (g)           Kc = 1.5 x 10^-3

Which of the following statements is correct if the initial concentrations are [A] = 0.85 M, [B] = 0.36 M, and [C] = 0.005 M.

A. At equilibrium, the amount of C will increase.

B. At equilibrium, the amount of A will increase.

C. At equilibrium, the amount of B will increase and C will increase.

D. At equilibrium, the amount of A will increase and B will decrease.

E. The reaction is at equilibrium.

The reaction

A + B ⇌ C + 2D

has an equilibrium constant of 3.7 x 10 ^-3 . Consider a reaction mixture with:

[A] = 2.0 x 10^-2 M

[B] = 1.7 x 10^-4 M

[C] = 2.4 x 10^-6 M

[D] = 3.5 x 10^-3 M

Which of the following statements is definitely true?

1. No conclusions about the system can be made without additional information.
2. The system is at equilibrium.
3. The reverse reaction will occur to a greater extent than the forward reaction until equilibrium is established.
4. The forward reaction will occur to a greater extent than the reverse reaction until equilibrium is established.

The reaction shown below has K_p = 81.9 at 25°C.

I₂(g) + Cl₂(g) ⇌ 2 ICl(g)

A flask contains P_i2 = 0.114 atm, P_Cl2 = 0.102 atm, and P_ICl = 0.355 atm. Choose the answer that best describes how this mixture will behave.

A) The reaction is at equlibrium, so the concentrations will not vary.

B) The reaction is not at equilibrium and will generate more products.

C) The reaction is not at equilibrium and will generate more reactants.

D) The reaction will not proceed without the addition of a catalyst.

E) The rate constant of the reaction is needed to solve this problem.

The value of the equilibrium constant at a given temperature for the reaction:

                2HI(g) ⇌ H₂(g) + I₂(g)

        is 0.200.  If [HI] = 0.200 M, [H ₂] = 0.200 M, and [I ₂] = 0.200 M, determine if the reaction is at equilibrium. If it is not, in which direction will it proceed to reach equilibrium?

    A)    The reaction is at equilibrium.

    B)    The reaction is not at equilibrium, it will shift to the left.

    C)    The reaction is not at equilibrium, it will shift to the right.

    D)    It is not possible to tell if the reaction is at equilibrium.

    E)    To reach equilibrium, the value of K_eq must change.

At a certain temperature, bromine and nitric oxide react to form nitrosyl bromide:

Br ₂(g) + 2 NO(g) ⇌ 2 NOBr(g). When initial amounts of Br ₂, NO, and NOBr are mixed, the concentration of NOBr increases. Which statement below is TRUE?

A) K _c < Q                                  B) K _c = Q                       C) K _c > Q         D) More information is needed to make a statement about Kc.

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.

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

Consider the following reaction at equilibrium at 24°C:

NH₄HS(s) ⇌ NH₃(g) + H₂S(g)      Kc = 1.58 x 10^–4

If 0.0205 mol of NH₃(g), 0.00800 mol of H₂S, and excess solid NH₄HS are mixed in a one-liter container at 24°C, in what direction will the equilibrium proceed?

The equilibrium constant Kc for the reaction

2 NOCl(g) → 2 NO(g) + Cl₂(g)

is 0.51 at a certain temperature. A mixture of NOCl, NO, and Cl2 with concentrations 1.3,1.2, and 0.60 M, respectively, was introduced into a container at this temperature. Which of the following is true?

1. Cl₂(g) is produced until equilibrium is reached.

2. [Cl₂ ] = 0.30 M at equilibrium.

3. No apparent reaction takes place. 

4. [NOCl] = [NO] = [Cl₂ ] at equilibrium.

5. NOCl(g) is produced until equilibrium is reached.

Write the reaction quotient for

For the following chemical reaction: Br ₂(g) + Cl₂(g) ⇌ 2BrCl(g)

At 400 K, the equilibrium constant is K p = 7.0. A closed vessel at 400 K is filled with 1.00 atm of Br₂(g), 1.00 atm of Cl₂(g), and 2.00 atm of BrCl(g). Use Q _p to determine which of the statements below is true.

A) At equilibrium, the total pressure in the vessel will be less than the initial total pressure.

B) The equilibrium partial pressure of Br ₂(g) will be greater than 1.00 atm.

C) The reaction will go to completion.

D) The equilibrium partial pressure of BrCl(g) will be greater than 2.00 atm.

E) The reaction shifts to the left

Consider the following reaction and its equilibrium constant:

I_2(g) ⇌ 2I_(g)                K _p = 0.209

A reaction mixture contains 0.89 atm I ₂ and 1.77 atm I. Which of the following statements is TRUE concerning this system?

A) The reaction will shift in the direction of reactants.

B) The reaction quotient will increase.

C) The reaction will shift in the direction of products.

D) The equilibrium constant will decrease.

E) The system is at equilibrium.

Which of the following statements is TRUE?

A) Dynamic equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction.

B) The equilibrium constant for the forward reaction is equal to the equilibrium constant for the reverse reaction.

C) A reaction quotient (Q) larger than the equilibrium constant (K) means that the reaction will favor the production of more products.

D) Dynamic equilibrium indicates that the amount of reactants and products are equal.

E) All of the above are true.

In a reaction mixture containing only reactants, what is the value of Q?

A) -1

B) 1

C) ∞

D) 0

E) It cannot be determined without concentrations.

Give the direction of the reaction, if Q >> 1

A) The forward reaction is favored.

B) The reverse reaction is favored.

C) cannot be determined.

D) If the temperature is raised, then the forward reaction is favored.

E) If the temperature is raised, then the reverse reaction is favored.

For the reaction:

PCl₃ (g) + Cl₃ (g) ⇌ PCl₅ (g)           K _c = 24.3

a system is prepared with

[PCl₃] = 0.10 M; [Cl ₂] = 0.15 M; [PCl ₅] = 0.60 M.

Which response is correct? 

a. the reaction is at equilibrium and concentrations will not change

b. the amount of PCl ₅ will increase

c. more PCl₃ will form

d. the reaction will shift right

e. the amount of PCl ₃ will increase while the concentration of Cl ₂ will decrease.

The reaction 2 A → B + C has a K_c of 0.2. The reaction is commenced with initial concentrations [A] = 0.2 M, [B] = 0.2 M and [C] = 0.2 M. In what direction does the reaction occur?

1. Cannot be determined without knowing the temperature.

2. The reaction shifts to the right to reach equilibrium

3. The reaction is already at equilibrium

4. The reaction shifts to the left to reach equilibrium.

What is the difference between the reaction quotient, Q, and the equilibrium constant, K, for a given chemical reaction? 

A mixture of 0.2 moles of H₂S(g), 0.5 moles of S₈(s), and 0.35 moles of H₂(g) is placed in a 2L container where the equilibrium

8H₂S(g) ⇌ 8H₂(g) + S₈(s)

is established. If the equilibrium constant for this reaction is K_c = 162, which of the following statements is true?

a) Q = 162 and the reaction is already at equilibrium.

b) Q = 44 and the reaction proceeds to the left

c) Q = 88 and the reaction proceeds to the right

d) Q = 44 and the reaction proceeds to the right

e) Q = 88 and the reaction proceeds to the left

For the reaction below K_c = 168

C(s) + CO₂(g) ⇌ 2CO(g)

A mixture contains some C(s), [CO] = 0.50 M and [CO ₂] = 0.75 M. Therefore the system will

a) Shift to produce more C (s) and CO₂ (g) because Q < K.

b) Shift to produce more CO because Q < K.

c) Shift to produce more C (s) and CO₂ (g) because Q > K.

d) Shift to produce more CO because Q > K.

e) The system is already in equilibrium

The reaction

2 NO_(g) + Br_2(g) ⟺ 2NOBr_(g)

has an equilibrium constant of 116.6  at 25°C. If Mickey Mouse starts with the reaction mixture P_NO = 0.300, P_Br2 = 0.225, P_NOBr = 0.855 at 25°C, predict what will happen as the reaction proceeds towards equilibrium. The initial partial pressures are given in atm.

a) More reactants will form

b) More products will form

c) The reaction is already at equilibrium

d) It is impossible for the process to come to equilibrium from these starting conditions

e) Not enough information is given

Given the chemical reaction:

4 H₃PO₄ (aq) ⇌ 6 H₂ (g) + 8 O₂ (g) + P₄ (s)              Kc = 1.35 X 10  ⁻¹²

Which direction will the reaction move if there is initially 0.25 M H ₃PO₄, 0.0020 M H₂, 0.150 M O₂ and 61.94 grams of P₄.

a. The reaction will move to the right because Q = 2.1 X 10  ^-21

b. The reaction will move to the right because Q = 4.2 X 10 ⁻²¹

c. The reaction will move to the left because Q = 2.1 X 10 ⁻²¹

d. The reaction will move to the left because Q = 4.2 X 10 ⁻²¹

e. The reaction will move to the right because Q = 0.0012

If a 1.00 L vessel contains 0.010 atm SO₃, 0.010 atm O₂, and 0.020 atm SO₂, is the system at equilibrium with respect to the reaction below? If not, what will happen in order to establish equilibrium?

2 SO₂ + O_2 ⇌ 2 SO₃                   Kp = 0.14