Question 1

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

Accepted Answer

A)  KP = Kc 
B)  KP = RT × Kc 
C)  KP = (RT × Kc )-1 
D)  KP = Kc/RT 
E)  KP = RT/Kc 
A)  KP = Kc 
B)  KP = RT × Kc 
C)  KP = (RT × Kc )-1 
D)  KP = Kc/RT 
E)  KP = RT/Kc B

Question 2

Find the temperature at which KP = 42.0 for the reaction H2(g) + I2(g)   2HI(g). [Given: at 25°C, for H2(g), ΔH°f = 0, S° = 131.0 J/mol • K; for I2(g), ΔH°f = 62.26 kJ/mol, S° = 260.6 J/mol • K; for HI(g), ΔH°f = 25.9 kJ/mol, S° = 206.3 J/mol • K; assume that ΔH° and ΔS° are independent of temperature.]

Accepted Answer

A)  1040 K 
B)  168 K 
C)  539 K 
D)  1400 K 
E)  34,200 K 
A)  1040 K 
B)  168 K 
C)  539 K 
D)  1400 K 
E)  34,200 K A

Question 3

Which is the correct equilibrium constant expression for the following reaction? 2C6H6(g) + 15O2(g)   12CO2(g) + 6H2O(g)

Accepted Answer

A)    
B)    
C)    
D)    
E)    
A)    
B)    
C)    
D)    
E)    B

Question 4

The equilibrium constant, KP, 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 Kc? (R = 0.08206 L • atm/K • mol)

Accepted Answer

A)  2.5 × 10-7 
B)  6.5 × 10-4 
C)  1.6 × 10-2 
D)  1.7 
E)  None of these choices is correct. 
A)  2.5 × 10-7 
B)  6.5 × 10-4 
C)  1.6 × 10-2 
D)  1.7 
E)  None of these choices is correct.

Question 5

For the following reaction at equilibrium in a reaction vessel, which one of these changes would cause the I2 concentration to increase? 2NOI(g)   2NO(g) + I2(g), ΔHºrxn = 45.3 kJ/mol

Accepted Answer

A)  Add more NOI 
B)  Add more NO 
C)  Increase the pressure 
D)  Compress the gas mixture into a smaller volume 
E)  Decrease the temperature 
A)  Add more NOI 
B)  Add more NO 
C)  Increase the pressure 
D)  Compress the gas mixture into a smaller volume 
E)  Decrease the temperature

Question 6

Solid ammonium hydrogen sulfide is introduced into a 2.00-L flask, and the flask is sealed. If this solid decomposes according to the equation NH4HS(s)   NH3(g) + H2S(g), KP = 0.108 at 25°C,
What is the minimum mass of ammonium hydrogen sulfide that must be present in the flask initially if equilibrium is to be established at 25°C? (R = 0.08206 L • atm/K • mol)

Accepted Answer

A)  0.917 g 
B)  1.37 g 
C)  2.74 g 
D)  0.581 g 
E)  0.452 g 
A)  0.917 g 
B)  1.37 g 
C)  2.74 g 
D)  0.581 g 
E)  0.452 g

Question 7

a. State Le Châtelier's principle.
b. The following reaction is at equilibrium in a closed container:
2Fe(OH)3(s)   Fe2O3(s) + 3H2O(g); ΔH°rxn > 0
What effects, if any, will the following actions have on the position of equilibrium? In each case, state the direction of any shift in equilibrium, and give your reasons in one sentence.
(i) adding more Fe(OH)3
(ii) raising the temperature
(iii) adding a more water vapor

Accepted Answer

a. If a stress is applied to a system at

Question 8

Stearic acid, nature's most common fatty acid, dimerizes when dissolved in hexane: 2C17H35COOH   (C17H35COOH)2; ΔH°rxn = -172 kJ/mol
The equilibrium constant for this reaction at 28°C is 2.9 × 103. Estimate the equilibrium constant at 38°C. (R = 8.314 J/K• mol)

Accepted Answer

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

Question 9

In the gas phase, methyl isonitrile (CH3NC) isomerizes to acetonitrile (CH3CN), H3C-N≡C(g)   H3C-C≡N(g)
With ΔH° = -89.5 kJ/mol and ΔG° = - 73.8 kJ/mol at 25°C. Find the equilibrium constant for this reaction at 100°C.

Accepted Answer

A)  1.68 × 10-10 
B)  5.96 × 109 
C)  2.16 × 1010 
D)  4.63 × 10-11 
E)  8.64 × 1012 
A)  1.68 × 10-10 
B)  5.96 × 109 
C)  2.16 × 1010 
D)  4.63 × 10-11 
E)  8.64 × 1012

Question 10

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? (R = 8.314 J/K• mol) 2HI(g)   H2(g) + I2(g)Kc = 0.020 at T = 453°C

Accepted Answer

A)  6.4 kJ/mol 
B)  8.8 kJ/mol 
C)  15 kJ/mol 
D)  19 kJ/mol 
E)  24 kJ/mol 
A)  6.4 kJ/mol 
B)  8.8 kJ/mol 
C)  15 kJ/mol 
D)  19 kJ/mol 
E)  24 kJ/mol

Question 11

Iron(III) oxide can be reduced by carbon monoxide. Fe2O3(s) + 3CO(g)   2Fe(s) + 3CO2(g)
Use the following thermodynamic data at 298 K to determine the equilibrium constant at this temperature. (R = 8.314 J/K • mol)

Accepted Answer

A)  7.0 × 10-6 
B)  1.3 × 10-3 
C)  2.2 × 104 
D)  1.4 × 105 
E)  > 2.0 × 105 
A)  7.0 × 10-6 
B)  1.3 × 10-3 
C)  2.2 × 104 
D)  1.4 × 105 
E)  > 2.0 × 105

Question 12

If one starts with pure NO2(g) at a pressure of 0.500 atm, the total pressure inside the reaction vessel when 2NO2(g)   2NO(g) + O2(g) reaches equilibrium is 0.674 atm. What is the equilibrium partial pressure of NO2?

Accepted Answer

A)  0.152 atm 
B)  0.174 atm 
C)  0.200 atm 
D)  0.326 atm 
E)  0.500 atm 
A)  0.152 atm 
B)  0.174 atm 
C)  0.200 atm 
D)  0.326 atm 
E)  0.500 atm

Question 13

When the following reaction is at equilibrium, which relationship is always true? 2NOCl(g)   2NO(g) + Cl2(g)

Accepted Answer

A)  [NO] [Cl2] = [NOCl] 
B)  [NO]2 [Cl2] = [NOCl]2 
C)  [NOCl] = [NO] 
D)  2[NO] = [Cl2] 
E)  [NO]2 [Cl2] = Kc[NOCl]2 
A)  [NO] [Cl2] = [NOCl] 
B)  [NO]2 [Cl2] = [NOCl]2 
C)  [NOCl] = [NO] 
D)  2[NO] = [Cl2] 
E)  [NO]2 [Cl2] = Kc[NOCl]2

Question 14

Hydrogen iodide decomposes according to the equation 2HI(g)   H2(g) + I2(g), for which Kc = 0.0156 at 400ºC. Suppose 0.550 mol HI is injected into a 2.00-L reaction vessel at 400ºC. What is the concentration of HI at equilibrium?

Accepted Answer

A)  0.138 M 
B)  0.220 M 
C)  0.550 M 
D)  0.275 M 
E)  0.0275 M 
A)  0.138 M 
B)  0.220 M 
C)  0.550 M 
D)  0.275 M 
E)  0.0275 M

Question 15

A 6.0-L vessel was found to contain 1.0 mol BrCl3, 2.0 mol Br2 and 6.0 mol Cl2 at equilibrium. What is the equilibrium constant, Kc, for this equilibrium mixture for the reaction
2BrCl3(g)   Br2(g) + 3Cl2(g)?

Accepted Answer

A)  0.014 
B)  108 
C)  18 
D)  12 
E)  432 
A)  0.014 
B)  108 
C)  18 
D)  12 
E)  432

Question 16

There are guidelines to help write equilibrium constants.

Accepted Answer

A) True 
 B)False

Question 17

For the endothermic reaction A2(g)   2A(g), a snapshot of an equilibrium mixture of A(g) and A2(g) may look as follows. (Each circle represents 1.0 mol of A atoms, and the volume of the box is 1.0 L.)   What is the equilibrium constant Kc for this reaction at 298 K? (R = 0.08206 L • atm/K • mol)

Accepted Answer

A)  0.19 
B)  0.67 
C)  1.3 
D)  2.7 
E)  5.3 
A)  0.19 
B)  0.67 
C)  1.3 
D)  2.7 
E)  5.3

Question 18

Suppose 75.0 g of PCl5(g) is introduced into an evacuated 3.00-L vessel and allowed to reach equilibrium at 250ºC. PCl5(g)   PCl3(g) + Cl2(g)
If KP = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium? (R = 0.0821 atm • L/mol • K)

Accepted Answer

A)  2.88 atm 
B)  2.28 atm 
C)  4.54 atm 
D)  7.43 atm 
E)  9.69 atm 
A)  2.88 atm 
B)  2.28 atm 
C)  4.54 atm 
D)  7.43 atm 
E)  9.69 atm

Question 19

When the substances in the equation below are at equilibrium, at pressure, P, and temperature, T, the equilibrium can be shifted to favor the products by CuO(s) + H2(g)   H2O(g) + Cu(s) ΔHºrxn = -2.0 kJ/mol

Accepted Answer

A)  increasing the pressure by means of a moving piston at constant T. 
B)  increasing the pressure by adding an inert gas such as nitrogen. 
C)  decreasing the temperature. 
D)  allowing some gases to escape at constant P and T. 
E)  adding a more copper. 
A)  increasing the pressure by means of a moving piston at constant T. 
B)  increasing the pressure by adding an inert gas such as nitrogen. 
C)  decreasing the temperature. 
D)  allowing some gases to escape at constant P and T. 
E)  adding a more copper.

Question 20

Suppose 15.00 g of solid ammonium hydrogen sulfide is introduced into a 500.-mL flask at 25°C, the flask is sealed, and the system is allowed to reach equilibrium. What is the partial pressure of ammonia in this flask if KP = 0.108 at 25°C for the following reaction? NH4HS(s)   NH3(g) + H2S(g)

Accepted Answer

A)  0.657 atm 
B)  1.25 atm 
C)  0.329 atm 
D)  14.4 atm 
E)  2.50 atm 
A)  0.657 atm 
B)  1.25 atm 
C)  0.329 atm 
D)  14.4 atm 
E)  2.50 atm

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?

Which is the correct equilibrium constant expression for the following reaction? 2C₆H₆(g) + 15O₂(g) 12CO₂(g) + 6H₂O(g)

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? (R = 0.08206 L • atm/K • mol)

For the following reaction at equilibrium in a reaction vessel, which one of these changes would cause the I₂ concentration to increase? 2NOI(g) 2NO(g) + I₂(g), ΔHº_rxn= 45.3 kJ/mol

Stearic acid, nature's most common fatty acid, dimerizes when dissolved in hexane: 2C₁₇H₃₅COOH (C₁₇H₃₅COOH)₂; ΔH°_rxn = -172 kJ/mol The equilibrium constant for this reaction at 28°C is 2.9 × 10³. Estimate the equilibrium constant at 38°C. (R = 8.314 J/K• mol)

In the gas phase, methyl isonitrile (CH₃NC) isomerizes to acetonitrile (CH₃CN), H₃C-N≡C(g) H₃C-C≡N(g) With ΔH° = -89.5 kJ/mol and ΔG° = - 73.8 kJ/mol at 25°C. Find the equilibrium constant for this reaction at 100°C.

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? (R = 8.314 J/K• mol) 2HI(g) H₂(g) + I₂(g)K_c = 0.020 at T = 453°C

Iron(III) oxide can be reduced by carbon monoxide. Fe₂O₃(s) + 3CO(g) 2Fe(s) + 3CO₂(g) Use the following thermodynamic data at 298 K to determine the equilibrium constant at this temperature. (R = 8.314 J/K • mol)

If one starts with pure NO₂(g) at a pressure of 0.500 atm, the total pressure inside the reaction vessel when 2NO₂(g) 2NO(g) + O₂(g) reaches equilibrium is 0.674 atm. What is the equilibrium partial pressure of NO₂?

When the following reaction is at equilibrium, which relationship is always true? 2NOCl(g) 2NO(g) + Cl₂(g)

Hydrogen iodide decomposes according to the equation 2HI(g) H₂(g) + I₂(g), for which K_c = 0.0156 at 400ºC. Suppose 0.550 mol HI is injected into a 2.00-L reaction vessel at 400ºC. What is the concentration of HI at equilibrium?

A 6.0-L vessel was found to contain 1.0 mol BrCl₃, 2.0 mol Br₂ and 6.0 mol Cl₂at equilibrium. What is the equilibrium constant, K_c, for this equilibrium mixture for the reaction 2BrCl₃(g) Br₂(g) + 3Cl₂(g)?

There are guidelines to help write equilibrium constants.

Suppose 75.0 g of PCl₅(g) is introduced into an evacuated 3.00-L vessel and allowed to reach equilibrium at 250ºC. PCl₅(g) PCl₃(g) + Cl₂(g) If K_P = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium? (R = 0.0821 atm • L/mol • K)

When the substances in the equation below are at equilibrium, at pressure, P, and temperature, T, the equilibrium can be shifted to favor the products by CuO(s) + H₂(g) H₂O(g) + Cu(s) ΔHº_rxn = -2.0 kJ/mol

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Exam 15: Chemical Equilibrium

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

Which is the correct equilibrium constant expression for the following reaction? 2C6H6(g) + 15O2(g) 12CO2(g) + 6H2O(g)

The equilibrium constant, KP, 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 Kc? (R = 0.08206 L • atm/K • mol)

For the following reaction at equilibrium in a reaction vessel, which one of these changes would cause the I2 concentration to increase? 2NOI(g) 2NO(g) + I2(g), ΔHºrxn = 45.3 kJ/mol

Stearic acid, nature's most common fatty acid, dimerizes when dissolved in hexane: 2C17H35COOH (C17H35COOH)2; ΔH°rxn = -172 kJ/mol The equilibrium constant for this reaction at 28°C is 2.9 × 103. Estimate the equilibrium constant at 38°C. (R = 8.314 J/K• mol)

In the gas phase, methyl isonitrile (CH3NC) isomerizes to acetonitrile (CH3CN), H3C-N≡C(g) H3C-C≡N(g) With ΔH° = -89.5 kJ/mol and ΔG° = - 73.8 kJ/mol at 25°C. Find the equilibrium constant for this reaction at 100°C.

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? (R = 8.314 J/K• mol) 2HI(g) H2(g) + I2(g)Kc = 0.020 at T = 453°C

Iron(III) oxide can be reduced by carbon monoxide. Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g) Use the following thermodynamic data at 298 K to determine the equilibrium constant at this temperature. (R = 8.314 J/K • mol)

If one starts with pure NO2(g) at a pressure of 0.500 atm, the total pressure inside the reaction vessel when 2NO2(g) 2NO(g) + O2(g) reaches equilibrium is 0.674 atm. What is the equilibrium partial pressure of NO2?

When the following reaction is at equilibrium, which relationship is always true? 2NOCl(g) 2NO(g) + Cl2(g)

Hydrogen iodide decomposes according to the equation 2HI(g) H2(g) + I2(g), for which Kc = 0.0156 at 400ºC. Suppose 0.550 mol HI is injected into a 2.00-L reaction vessel at 400ºC. What is the concentration of HI at equilibrium?

A 6.0-L vessel was found to contain 1.0 mol BrCl3, 2.0 mol Br2 and 6.0 mol Cl2 at equilibrium. What is the equilibrium constant, Kc, for this equilibrium mixture for the reaction 2BrCl3(g) Br2(g) + 3Cl2(g)?

There are guidelines to help write equilibrium constants.

For the endothermic reaction A2(g) 2A(g), a snapshot of an equilibrium mixture of A(g) and A2(g) may look as follows. (Each circle represents 1.0 mol of A atoms, and the volume of the box is 1.0 L.) What is the equilibrium constant Kc for this reaction at 298 K? (R = 0.08206 L • atm/K • mol)

Suppose 75.0 g of PCl5(g) is introduced into an evacuated 3.00-L vessel and allowed to reach equilibrium at 250ºC. PCl5(g) PCl3(g) + Cl2(g) If KP = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium? (R = 0.0821 atm • L/mol • K)

When the substances in the equation below are at equilibrium, at pressure, P, and temperature, T, the equilibrium can be shifted to favor the products by CuO(s) + H2(g) H2O(g) + Cu(s) ΔHºrxn = -2.0 kJ/mol

Suppose 15.00 g of solid ammonium hydrogen sulfide is introduced into a 500.-mL flask at 25°C, the flask is sealed, and the system is allowed to reach equilibrium. What is the partial pressure of ammonia in this flask if KP = 0.108 at 25°C for the following reaction? NH4HS(s) NH3(g) + H2S(g)

Chemistry: the Central Science

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Chemical Bonding I: Basic Concepts

Chemical Bonding II: Molecular Geometry and Bonding Theories

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Intermolecular Forces and the Physical Properties of Liquids and Solids

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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?

Which is the correct equilibrium constant expression for the following reaction? 2C₆H₆(g) + 15O₂(g) 12CO₂(g) + 6H₂O(g)

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? (R = 0.08206 L • atm/K • mol)

For the following reaction at equilibrium in a reaction vessel, which one of these changes would cause the I₂ concentration to increase? 2NOI(g) 2NO(g) + I₂(g), ΔHº_rxn= 45.3 kJ/mol

Stearic acid, nature's most common fatty acid, dimerizes when dissolved in hexane: 2C₁₇H₃₅COOH (C₁₇H₃₅COOH)₂; ΔH°_rxn = -172 kJ/mol The equilibrium constant for this reaction at 28°C is 2.9 × 10³. Estimate the equilibrium constant at 38°C. (R = 8.314 J/K• mol)

In the gas phase, methyl isonitrile (CH₃NC) isomerizes to acetonitrile (CH₃CN), H₃C-N≡C(g) H₃C-C≡N(g) With ΔH° = -89.5 kJ/mol and ΔG° = - 73.8 kJ/mol at 25°C. Find the equilibrium constant for this reaction at 100°C.

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? (R = 8.314 J/K• mol) 2HI(g) H₂(g) + I₂(g)K_c = 0.020 at T = 453°C

Iron(III) oxide can be reduced by carbon monoxide. Fe₂O₃(s) + 3CO(g) 2Fe(s) + 3CO₂(g) Use the following thermodynamic data at 298 K to determine the equilibrium constant at this temperature. (R = 8.314 J/K • mol)

If one starts with pure NO₂(g) at a pressure of 0.500 atm, the total pressure inside the reaction vessel when 2NO₂(g) 2NO(g) + O₂(g) reaches equilibrium is 0.674 atm. What is the equilibrium partial pressure of NO₂?

When the following reaction is at equilibrium, which relationship is always true? 2NOCl(g) 2NO(g) + Cl₂(g)

Hydrogen iodide decomposes according to the equation 2HI(g) H₂(g) + I₂(g), for which K_c = 0.0156 at 400ºC. Suppose 0.550 mol HI is injected into a 2.00-L reaction vessel at 400ºC. What is the concentration of HI at equilibrium?

A 6.0-L vessel was found to contain 1.0 mol BrCl₃, 2.0 mol Br₂ and 6.0 mol Cl₂at equilibrium. What is the equilibrium constant, K_c, for this equilibrium mixture for the reaction 2BrCl₃(g) Br₂(g) + 3Cl₂(g)?

Suppose 75.0 g of PCl₅(g) is introduced into an evacuated 3.00-L vessel and allowed to reach equilibrium at 250ºC. PCl₅(g) PCl₃(g) + Cl₂(g) If K_P = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium? (R = 0.0821 atm • L/mol • K)

When the substances in the equation below are at equilibrium, at pressure, P, and temperature, T, the equilibrium can be shifted to favor the products by CuO(s) + H₂(g) H₂O(g) + Cu(s) ΔHº_rxn = -2.0 kJ/mol