Question 1

The equilibrium constant for the reaction below is 7.2 x 10^-4 at 298 K and 1 atm. HNO₂(aq) + H₂O(l) ⇌ NO₂^-(aq) + H₃O⁺(aq) When [HNO₂(aq)] = 1.0 M and [NO₂^-(aq)] = [H₃O⁺(aq)] = 1.0 x 10^-5 M, calculate ΔG. A) -39.1 kJ/mol B) +17.9 kJ/mol C) -17.9 kJ/mol D) +39.1 kJ/mol

Accepted Answer

The reaction quotient, Q, is calculated as:Q = [NO2-] [H3O+] / [HNO2] = (1.0 x 10^-5) (1.0 x 10^-5) / 1.0 = 1.0 x 10^-10Since Q < K, the reaction will proceed in the forward direction to reach equilibrium. The change in free energy, ΔG, is calculated using the equation:ΔG = -RT ln(Q/K) = -(8.314 J/mol K) (298 K) ln(1.0 x 10^-10 / 7.2 x 10^-4) = -39.1 kJ/molTherefore, the correct answer is A) -39.1 kJ/mol.

Question 2

For the reaction: CO(g) + 2 H₂(g) → CH₃OH(g) Kp = 91.4 at 350 K and Kp = 2.05 × 10^-4 at 298 K. What is the value of ΔH°? A) 49.9 kJ/mol B) 2.08 × 10³ kJ/mol C) 3.74 × 10^-2 kJ/mol D) 217 kJ/mol E) 446 kJ/mol

Accepted Answer

The answer of For the reaction: CO(g) + 2 H₂(g)...

Question 3

For the reaction, CaCO₃(s) → CaO(s) + CO₂(g) S° (J/mol K) 88.70 39.75 213.6 What is ΔS°rxn? A) 262.5 J/mol ∙ K B) -85.1 J/mol ∙ K C) -164.7 J/mol ∙ K D) 164.7 J/mol ∙ K E) 85.1 J/mol ∙ K

Accepted Answer

ΔS°rxn = S°(products) - S°(reactants)= [S°(CaO) + S°(CO2)] - [S°(CaCO3)]= [(39.75 J/mol K) + (213.6 J/mol K)] - (88.70 J/mol K)= 164.7 J/mol K

Question 4

Consider the reaction: N₂(g) + 3 X₂(g) → 2 NX₃(g) △H° 0.0 0.0 -43 kJ/mol S° 192 210 172 J/(mol∙K) What is Keq for this reaction at 591 K? A) 2.3 × 10¹⁷ B) 4.3 × 10^-18 C) 1.04 D) 0.96 E) 132

Accepted Answer

The answer of Consider the reaction: 
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Question 5

Predict whether ΔS is positive or negative for the following process: H₂O(g) → H₂O(s) A) negative B) positive C) There is not enough information to determine. D) ΔS doesn't change. E) ΔS changes the same on both sides of the equation.

Accepted Answer

The process involves the conversion of water vapor (gas) to ice (solid). This transition from a more disordered state (gas) to a more ordered state (solid) results in a decrease in entropy, making ΔS negative.

Question 6

Choose the INCORRECT statement.
A) The van't Hoff equation is ln  =
 .
B) Keq is independent of temperature.
C) In a thermodynamic equilibrium constant expression, the activity of a gas is replaced by its partial pressure in atmosphere.
D) In a Keq expression, the activity of a solution is replaced by its molarity.
E) If ΔG = 0, the process is at equilibrium.

Accepted Answer

The answer of Choose the INCORRECT statement.
A) The van't Hoff...

Question 7

Order the following by increasing entropy. CO(g), COCl₂(g), CO₂(g), CaO(s) A) CO₂ < CO < CaO < COCl₂ B) CaO < CO < CO₂ < COCl₂ C) COCl₂ < CO < CaO < CO₂ D) CO₂ < CaO < COCl₂ < CO E) CO < CaO < COCl₂ < CO₂

Accepted Answer

Entropy increases with increasing disorder or randomness. Going from solid to gas increases disorder, so CaO(s) will have the lowest entropy. CO(g) and CO₂(g) are both gases, but CO₂(g) has a greater molar mass and therefore more atoms to contribute to disorder, so it will have a higher entropy than CO(g). Finally, COCl₂(g) has three different atoms and a larger molar mass than both CO(g) and CO₂(g), so it will have the highest entropy. Therefore, the correct order from lowest to highest entropy is CaO < CO < CO₂ < COCl₂, which is represented by option B.

Question 8

Which of the following quantities is generally independent of temperature? I) ΔH
II) ΔS
III) ΔG
A) I only
B) II only
C) III only
D) I and II
E) I, II, and III

Accepted Answer

ΔH and ΔS are generally independent of temperature, while ΔG is not.

Question 9

Predict whether ΔS is positive or negative for the following process: 2 Cl₂O₇(g) → 2 Cl₂(g) + 7 O₂(g) A) negative B) positive C) There is not enough information to determine. D) ΔS doesn't change. E) ΔS changes the same on both sides of the equation.

Accepted Answer

The reaction involves the formation of three gases from two gases. Gases have higher entropy than solids or liquids, so the entropy of the system is likely to increase, making ΔS positive.

Question 10

For the reaction PCl₅(g) → PCl₃(g) + Cl₂(g) at 298 K, Keq = 1.87 × 10^-7, ΔS° = 1.8192 J/(mol ∙K), what is ΔG° and is the reaction spontaneous? A) 3.84 × 10⁴ kJ/mol, no B) 7.68 kJ/mol, no C) -7.68 kJ/mol, yes D) 38.4 kJ/mol, no E) -38.4 kJ/mol, yes

Accepted Answer

The answer of For the reaction PCl₅(g) → PCl₃(g) +...

Question 11

If the vapor pressure of water in an open system at 25°C is 23.8 mmHg, what is ΔG for the reaction below at 25°C? H₂O(l) → H₂O(g, 23.8 mmHg) A) 0 kJ/mol B) -8.58 kJ/mol C) +8.58 kJ/mol D) -0.720 kJ/mol

Accepted Answer

At equilibrium, the Gibbs free energy change (ΔG) for a process is zero. Since the vapor pressure of water is given as 23.8 mmHg, which is the equilibrium vapor pressure at 25°C, ΔG for the phase transition is 0 kJ/mol.

Question 12

For Cl₂O(g) + 3/2 O₂(g) → 2 ClO₂ △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq? A) 0.97 B) 6.12 × 10^-7 C) 4.27 × 10^-22 D) 9.17 × 10^-15 E) 1.07 × 10¹⁴

Accepted Answer

The Gibbs free energy change (ΔG°) can be calculated using ΔG° = ΔH° - TΔS°. At 377°C (650K), ΔG° = 126,000 J/mol - 650K * (-74.9 J/(mol∙K)) = 174,185 J/mol. Keq is calculated using ΔG° = -RTln(Keq), leading to Keq = e^(-ΔG°/RT). Solving gives Keq ≈ 9.17 × 10^-15.

Question 13

Choose the INCORRECT statement about coupled reactions.
A) The usual practice of coupling reactions is to join two nonspontaneous reactions.
B) The usual reason to couple reactions is to produce an overall spontaneous reaction.
C) The reaction added to a nonspontaneous reaction needs to be spontaneous.
D) The reaction added to a nonspontaneous reaction needs to be more spontaneous than the original reaction is nonspontaneous.
E) One of the coupled reactions has a negative ΔG, the other a positive ΔG.

Accepted Answer

The usual practice of coupling reactions is to join a nonspontaneous reaction with a spontaneous one, not two nonspontaneous reactions.

Question 14

For the reaction, CO(g) + 2H₂(g) → CH₃OH(g) S° (J/mol K) 197.6 130.6 239.7 What is ΔS°rxn? A) -88.5 J/mol ∙ K B) -176.7 J/mol ∙ K C) 219 J/mol ∙ K D) 176.7 J/mol ∙ K E) -219.1 J/mol ∙ K

Accepted Answer

To calculate ΔS°rxn, we use the formula:

ΔS°rxn = ΣnS°(products) - ΣmS°(reactants)

Where Σn and Σm are the stoichiometric coefficients of the products and reactants, respectively, and S° is the standard molar entropy.

Using the values given in the table, we have:

ΔS°rxn = (1 mol x 213.7 J/mol K) - (1 mol x 197.6 J/mol K + 2 mol x 130.6 J/mol K)
ΔS°rxn = 213.7 J/mol K - 459.8 J/mol K
ΔS°rxn = -246.1 J/mol K

However, the answer choices are given in kJ/mol K. So we convert our answer:

ΔS°rxn = -246.1 J/mol K = -0.2461 kJ/mol K

Rounding to one decimal place, we get:

ΔS°rxn = -0.2 kJ/mol K

Therefore, the best choice is E (-219.1 J/mol ∙ K), as it is the closest to our calculated value, taking into account the rounding.

Question 15

Predict whether ΔS is positive or negative for the following process: H₂(g) + 1/2 O₂(g) → H₂O(g) A) negative B) positive C) There is not enough information to determine. D) ΔS doesn't change. E) ΔS changes the same on both sides of the equation.

Accepted Answer

The process involves the combination of two gas molecules (H₂ and O₂) to form one gas molecule (H₂O), which results in a decrease in the number of gas molecules and thus a decrease in entropy (ΔS is negative).

Question 16

Consider the reaction of 25.0 mL of 0.20 M AgNO₃(aq) with 25.0 mL of 0.20 M NaBr(aq) to form AgBr(s) at 25°C. What is ΔG for this reaction? The Ksp of AgBr is 5.0 x 10^-13 at 25°C. A) -58.8 kJ/mol B) -70.2 kJ/mol C) +58.8 kJ/mol D) +70.2 kJ/mol

Accepted Answer

The reaction quotient Q is much larger than Ksp, indicating the reaction will proceed to form AgBr(s). ΔG can be calculated using ΔG = -RTln(K), where K is the equilibrium constant (1/Ksp for precipitation reactions). This results in a negative ΔG, indicating a spontaneous reaction.

Question 17

For the reaction, N₂O₄(g) → 2 NO₂(g) S° (J/mol K) 304.2 240.0 What is ΔS°rxn? A) 544.2 J/mol ∙ K B) -64.2 J/mol ∙ K C) 175.8 J/mol ∙ K D) -175.8 J/mol ∙ K E) 64.2 J/mol ∙ K

Accepted Answer

The answer of For the reaction, N₂O₄(g) → 2 NO₂(g)...

Question 18

Which of the listed reactions would couple with the following reaction to produce silver? Ag₂O(s) → 2 Ag(s) + 1/2 O(g) ΔG° = 11.2 kJ/mol A) Ag(s) + 1/2 Br2 → AgBr(s) ΔG° = 96.9 kJ/mol B) C + 1/2 O₂ → CO ΔG° = -137.2 kJ/mol C) N + 1/2 O₂ → NO ΔG° = 149.3 kJ/mol D) N + O₂ → NO₂ ΔG° = 51.3 kJ/mol E) C + 2 S → CS₂(l) ΔG° = 65.3 kJ/mol

Accepted Answer

The answer of Which of the listed reactions would couple...

Question 19

Which of the following quantities for an element has a value of zero in the standard state? I) ΔH°f
II) ΔG°f
III) S°
A) I only
B) II only
C) III only
D) I and II
E) I, II, and III

Accepted Answer

In the standard state, the standard enthalpy of formation (ΔH°f) and the standard Gibbs free energy of formation (ΔG°f) for an element in its most stable form are both zero. However, the standard entropy (S°) is not zero for elements in their standard state.

Question 20

For the vaporization of water in an open system at 25°C and 1 atm, which of the following is correct?
A) The reaction is entropy driven.
B) The reaction is enthalpy driven.
C) The reaction is not spontaneous.
D) ΔG°rxn = 0

Accepted Answer

The vaporization of water at 25°C and 1 atm is an entropy-driven process because the change in entropy (ΔS) for the system is positive. The molecules in the liquid phase have more freedom of movement and entropy than in the highly ordered and structured solid phase, allowing for more disorder during the phase change to gas. The enthalpy change (ΔH) for the reaction is also positive, meaning that energy is required to break the intermolecular bonds holding the liquid together to form vapor. However, since the reaction is occurring in an open system, there is no pressure difference to drive the reaction towards the gas phase, making the reaction non-spontaneous. Therefore, ΔG°rxn is positive, indicating that the reaction is non-spontaneous under standard conditions.

Quiz 19: Spontaneous Change: Entropy and Free Energy

The equilibrium constant for the reaction below is 7.2 x 10^-4 at 298 K and 1 atm. HNO₂(aq) + H₂O(l) ⇌ NO₂^-(aq) + H₃O⁺(aq) When [HNO₂(aq) ] = 1.0 M and [NO₂^-(aq) ] = [H₃O⁺(aq) ] = 1.0 x 10^-5 M, calculate ΔG.

For the reaction: CO(g) + 2 H₂(g) → CH₃OH(g) Kp = 91.4 at 350 K and Kp = 2.05 × 10^-4 at 298 K. What is the value of ΔH°?

For the reaction, CaCO₃(s) → CaO(s) + CO₂(g) S° (J/mol K) 88.70 39.75 213.6 What is ΔS°rxn?

Consider the reaction: N₂(g) + 3 X₂(g) → 2 NX₃(g) △H° 0.0 0.0 -43 kJ/mol S° 192 210 172 J/(mol∙K) What is Keq for this reaction at 591 K?

Predict whether ΔS is positive or negative for the following process: H₂O(g) → H₂O(s)

Choose the INCORRECT statement.

Order the following by increasing entropy. CO(g) , COCl₂(g) , CO₂(g) , CaO(s)

Which of the following quantities is generally independent of temperature? I) ΔH II) ΔS III) ΔG

Predict whether ΔS is positive or negative for the following process: 2 Cl₂O₇(g) → 2 Cl₂(g) + 7 O₂(g)

For the reaction PCl₅(g) → PCl₃(g) + Cl₂(g) at 298 K, Keq = 1.87 × 10^-7, ΔS° = 1.8192 J/(mol ∙K) , what is ΔG° and is the reaction spontaneous?

If the vapor pressure of water in an open system at 25°C is 23.8 mmHg, what is ΔG for the reaction below at 25°C? H₂O(l) → H₂O(g, 23.8 mmHg)

For Cl₂O(g) + 3/2 O₂(g) → 2 ClO₂ △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq?

Choose the INCORRECT statement about coupled reactions.

For the reaction, CO(g) + 2H₂(g) → CH₃OH(g) S° (J/mol K) 197.6 130.6 239.7 What is ΔS°rxn?

Predict whether ΔS is positive or negative for the following process: H₂(g) + 1/2 O₂(g) → H₂O(g)

Consider the reaction of 25.0 mL of 0.20 M AgNO₃(aq) with 25.0 mL of 0.20 M NaBr(aq) to form AgBr(s) at 25°C. What is ΔG for this reaction? The Ksp of AgBr is 5.0 x 10^-13 at 25°C.

For the reaction, N₂O₄(g) → 2 NO₂(g) S° (J/mol K) 304.2 240.0 What is ΔS°rxn?

Which of the listed reactions would couple with the following reaction to produce silver? Ag₂O(s) → 2 Ag(s) + 1/2 O(g) ΔG° = 11.2 kJ/mol

Which of the following quantities for an element has a value of zero in the standard state? I) ΔH°f II) ΔG°f III) S°

For the vaporization of water in an open system at 25°C and 1 atm, which of the following is correct?

Quiz 19: Spontaneous Change: Entropy and Free Energy

The equilibrium constant for the reaction below is 7.2 x 10-4 at 298 K and 1 atm. HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq) When [HNO2(aq) ] = 1.0 M and [NO2-(aq) ] = [H3O+(aq) ] = 1.0 x 10-5 M, calculate ΔG.

For the reaction: CO(g) + 2 H2(g) → CH3OH(g) Kp = 91.4 at 350 K and Kp = 2.05 × 10-4 at 298 K. What is the value of ΔH°?

For the reaction, CaCO3(s) → CaO(s) + CO2(g) S° (J/mol K) 88.70 39.75 213.6 What is ΔS°rxn?

Consider the reaction: N2(g) + 3 X2(g) → 2 NX3(g) △H° 0.0 0.0 -43 kJ/mol S° 192 210 172 J/(mol∙K) What is Keq for this reaction at 591 K?

Predict whether ΔS is positive or negative for the following process: H2O(g) → H2O(s)

Choose the INCORRECT statement.

Order the following by increasing entropy. CO(g) , COCl2(g) , CO2(g) , CaO(s)

Which of the following quantities is generally independent of temperature? I) ΔH II) ΔS III) ΔG

Predict whether ΔS is positive or negative for the following process: 2 Cl2O7(g) → 2 Cl2(g) + 7 O2(g)

For the reaction PCl5(g) → PCl3(g) + Cl2(g) at 298 K, Keq = 1.87 × 10-7, ΔS° = 1.8192 J/(mol ∙K) , what is ΔG° and is the reaction spontaneous?

If the vapor pressure of water in an open system at 25°C is 23.8 mmHg, what is ΔG for the reaction below at 25°C? H2O(l) → H2O(g, 23.8 mmHg)

For Cl2O(g) + 3/2 O2(g) → 2 ClO2 △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq?