Question 1

Which of the following reactions has the largest positive entropy change?

Accepted Answer

The answer of Which of the following reactions has the...

Question 2

The following reduction of Fe₂ O₃ to Fe occurs in blast furnaces during the steel making process: 3 CO (g) + Fe₂ O₃(s) 2 Fe (s) + 3 CO₂ (g) Calculate per mole of Fe₂ O₃ reacted, if the values of S for CO (g), Fe₂ O₃(s), Fe (s), and CO₂ (g) are 198, 87, 27, and 214 J/mol K, respectively (answer in units of J/K).

Accepted Answer

The answer of The following reduction of Fe₂ O₃ to...

Question 3

The third law of thermodynamics states that:

Accepted Answer

The third law of thermodynamics states that the entropy of a pure crystalline solid is zero at 0 K.

Question 4

For which of the following processes will D S _system be the most positive?

Accepted Answer

The answer of For which of the following processes will...

Question 5

Which of the following physical changes would be expected to have a negative sign for D S _system? I. Dissolving oxygen gas, O₂, in water. II. Freezing ice cubes. III. Breaking glass.

Accepted Answer

I and II involve a decrease in the disorder of the system. Dissolving gas into liquid and freezing water into ice both result in a more ordered state, which corresponds to a negative change in entropy ($ \Delta S $). Breaking glass, however, increases disorder, suggesting a positive $\Delta S$, and is not included.

Question 6

For the reaction 4 CuO (s)→2 Cu₂O (s) + O₂ (g), what is D S ° at 298 K (in J/K)? S ° [CuO] = 43 J/mol × K; S ° [O₂] = 205 J/mol × K; S ° [Cu₂O] = 93.14 J/mol × K

Accepted Answer

The change in standard entropy ($\Delta S^\circ$) for the reaction can be calculated using the formula $\Delta S^\circ = \sum S^\circ_{\text{products}} - \sum S^\circ_{\text{reactants}}$. For the given reaction, $\Delta S^\circ = [2(93.14) + 205] - [4(43)] = 186.28 + 205 - 172 = 219.28 \, \text{J/K}$. The closest value to this calculation is 219 J/K.

Question 7

Which of the following chemical equations would be expected to have a positive sign for D S _system? I. NaClO₃ (s)→Na⁺ (aq) + ClO₃^{1 -} (aq) II. NH₃ (g) + HBr (g)→NH₄Br (s) III. H₂S (g) + ¹/₂ O₂ (g)→¹/₈ S₈ (s) + H₂O (g)

Accepted Answer

The equation that represents a solid turning into two aqueous solutions (I) is likely to have a positive entropy change because solid particles are more ordered than dissolved ions. The other two equations involve the formation of a solid (II) or a gas reacting with another gas to form a solid (III), which are both examples of a decrease in entropy. Therefore, only equation I is expected to have a positive sign for ΔS.

Question 8

Which process below is accompanied by a decrease in entropy for the system ?

Accepted Answer

The answer of Which process below is accompanied by a...

Question 9

Which of the following reactions would be expected to have a positive entropy change , D S > 0? I. 3 O₂ (g)→2 O₃ (g) II. CaCO₃ (s)→CaO (s) + CO₂ (g) III. C₃H₈ (g) + 5 O₂ (g)→3 CO₂ (g) + 4 H₂O (g)

Accepted Answer

For a reaction to have a positive entropy change, there must be an increase in the number of moles of gas, or a dispersal of particles or energy. 
In option I, the reactants have 3 moles of gas while the products have 2 moles of gas, so the entropy change is negative, ΔS < 0. 
In option II, the reactants have 1 solid and 1 gas while the products have 1 solid and 1 gas, so the entropy change is likely to be small or slightly negative, ΔS ≈ 0 or ΔS slightly < 0. 
In option III, the reactants have 6 moles of gas while the products have 7 moles of gas, so the entropy change is positive, ΔS > 0. Therefore, the correct answer is E (II and III).

Question 10

Which of the following physical changes would be expected to provide a positive change in entropy , D S > 0?
I. Compressing a gas until it liquefies.
II. Melting an ice-cube.
III. Heating a substance to a higher temperature.

Accepted Answer

Melting an ice-cube and heating a substance both involve an increase in the disorder of the molecules, leading to an increase in entropy (DS>0). Compressing a gas, however, involves a decrease in volume and an increase in order, leading to a decrease in entropy (DS<0). Therefore, only melting an ice-cube and heating a substance to a higher temperature would result in a positive change in entropy.

Question 11

Using the entropy values in the table below, what is the change in standard entropy, D S , for the following reaction?
2 CH₃ OH (g) + 3 O₂(g) 2 CO₂ (g) + 4 H₂ O (g) Substance S (J/mol K) CH₃ OH (  ) 126.8 CH₃ OH (g) 237.6 O₂(g) 205.0 CO₂ (g) 213.6 H₂ O (g) 188.83 H₂ O (  ) 69.91

Accepted Answer

The answer of Using the entropy values in the table...

Question 12

"A spontaneous change is always accompanied by an increase in entropy." The entropy change referred to in this statement is:

Accepted Answer

The entropy change referred to in the statement is the change in entropy of the universe (system plus surroundings), which is represented by D S _universe. This is because a spontaneous change (one that occurs without any external influence or intervention) will always result in an increase in the entropy of the universe.

Question 13

Which of the following chemical reactions would be expected to have a positive sign for D S _reaction? I. 2 N₂ (g) + 3 F₂ (g)→2 NF₃ (g) II. NaCl (aq) + AgNO₃ (aq)→NaNO₃ (aq) + AgCl (s) III. CaCO₃ (s)→CaO (s) + CO₂ (g)

Accepted Answer

Reaction III involves the decomposition of a solid into a solid and a gas, which increases the disorder and thus has a positive entropy change (ΔS).

Question 14

Which of the following reactions would be expected to provide a negative change in entropy , D S I. 2 K (s) + F₂ (g)→2 KF (s) II. 2 NO₂ (g)→N₂O₄ (g) III. NaClO₃ (s)→Na⁺ (aq) + ClO₃^{1 -} (aq)

Accepted Answer

Reactions I and II both result in a decrease in the number of gas molecules, leading to a decrease in entropy. Reaction III involves the dissolution of a solid into ions in solution, which typically increases entropy.

Question 15

Which of the following chemical reactions has the largest positive entropy change?

Accepted Answer

Option B involves a reaction where the number of gas molecules increases from 2 to 3, which typically results in the largest positive change in entropy compared to the other options.

Question 16

Which of the following processes would be expected to have a positive sign for D S _system? I. Hot air expanding. II. A piece of wax melting. III. Alcohol evaporating.

Accepted Answer

All of these processes involve a transition to a more disordered state: hot air expanding increases the disorder by spreading out, wax melting from solid to liquid increases disorder, and alcohol evaporating from liquid to gas greatly increases disorder. Thus, all have a positive change in entropy ($ \Delta S > 0 $).

Question 17

The entropy change when one mole of acetone [(CH₃)₂CO] vaporizes at its boiling point (56 ° C) is D S _vap = 97.16 J/mol × K. How much heat is absorbed when 58.0 grams of acetone vaporizes at 56 ° C?

Accepted Answer

The answer of The entropy change when one mole of...

Question 18

Which of the following reactions would be expected to have a positive entropy change, D S 0? I. 2 SO₂ (g) + O₂(g) 2 SO₃(g) II. Ba(OH) 2 (s) BaO (s) + H₂ O (g) III. CO (g) + 2 H₂ (g) CH₃ OH ( )

Accepted Answer

The answer of Which of the following reactions would be...

Question 19

Which of the following processes results in a negative entropy change?

Accepted Answer

The answer of Which of the following processes results in...

Question 20

Estimate the normal boiling point of mercury, given that for Hg (  ),  = 0 kJ/mol and D S = 76.02 J/mol K and for Hg (g),  = 61.32 kJ/mol and D S = 174.85 J/mol K. The change is:
Hg (  )  Hg (g)

Accepted Answer

The answer of Estimate the normal boiling point of mercury,...

Quiz 17: Chemical Thermodynamics

Which of the following reactions has the largest positive entropy change?

The third law of thermodynamics states that:

For which of the following processes will D S _system be the most positive?

Which of the following physical changes would be expected to have a negative sign for D S _system? I. Dissolving oxygen gas, O₂, in water. II. Freezing ice cubes. III. Breaking glass.

For the reaction 4 CuO (s) →2 Cu₂O (s) + O₂ (g) , what is D S ° at 298 K (in J/K) ? S ° [CuO] = 43 J/mol × K; S ° [O₂] = 205 J/mol × K; S ° [Cu₂O] = 93.14 J/mol × K

Which of the following chemical equations would be expected to have a positive sign for D S _system? I. NaClO₃ (s) →Na⁺ (aq) + ClO₃^{1 -} (aq) II. NH₃ (g) + HBr (g) →NH₄Br (s) III. H₂S (g) + ¹/₂ O₂ (g) →¹/₈ S₈ (s) + H₂O (g)

Which process below is accompanied by a decrease in entropy for the system ?

Which of the following reactions would be expected to have a positive entropy change , D S > 0? I. 3 O₂ (g) →2 O₃ (g) II. CaCO₃ (s) →CaO (s) + CO₂ (g) III. C₃H₈ (g) + 5 O₂ (g) →3 CO₂ (g) + 4 H₂O (g)

Which of the following physical changes would be expected to provide a positive change in entropy , D S > 0? I. Compressing a gas until it liquefies. II. Melting an ice-cube. III. Heating a substance to a higher temperature.

Using the entropy values in the table below, what is the change in standard entropy, D S , for the following reaction? 2 CH₃ OH (g) + 3 O₂(g) 2 CO₂ (g) + 4 H₂ O (g) Substance S (J/mol K) CH₃ OH ( ) 126.8 CH₃ OH (g) 237.6 O₂(g) 205.0 CO₂ (g) 213.6 H₂ O (g) 188.83 H₂ O ( ) 69.91

"A spontaneous change is always accompanied by an increase in entropy." The entropy change referred to in this statement is:

Which of the following chemical reactions would be expected to have a positive sign for D S _reaction? I. 2 N₂ (g) + 3 F₂ (g) →2 NF₃ (g) II. NaCl (aq) + AgNO₃ (aq) →NaNO₃ (aq) + AgCl (s) III. CaCO₃ (s) →CaO (s) + CO₂ (g)

Which of the following reactions would be expected to provide a negative change in entropy , D S I. 2 K (s) + F₂ (g) →2 KF (s) II. 2 NO₂ (g) →N₂O₄ (g) III. NaClO₃ (s) →Na⁺ (aq) + ClO₃^{1 -} (aq)

Which of the following chemical reactions has the largest positive entropy change?

Which of the following processes would be expected to have a positive sign for D S _system? I. Hot air expanding. II. A piece of wax melting. III. Alcohol evaporating.

The entropy change when one mole of acetone [(CH₃) ₂CO] vaporizes at its boiling point (56 ° C) is D S _vap = 97.16 J/mol × K. How much heat is absorbed when 58.0 grams of acetone vaporizes at 56 ° C?

Which of the following reactions would be expected to have a positive entropy change, D S 0? I. 2 SO₂ (g) + O₂(g) 2 SO₃(g) II. Ba(OH) 2 (s) BaO (s) + H₂ O (g) III. CO (g) + 2 H₂ (g) CH₃ OH ( )

Which of the following processes results in a negative entropy change?

Estimate the normal boiling point of mercury, given that for Hg ( ) , = 0 kJ/mol and D S = 76.02 J/mol K and for Hg (g) , = 61.32 kJ/mol and D S = 174.85 J/mol K. The change is: Hg ( ) Hg (g)

Quiz 17: Chemical Thermodynamics

Which of the following reactions has the largest positive entropy change?

The third law of thermodynamics states that:

For which of the following processes will D S system be the most positive?

Which of the following physical changes would be expected to have a negative sign for D S system? I. Dissolving oxygen gas, O2, in water. II. Freezing ice cubes. III. Breaking glass.

For the reaction 4 CuO (s) →2 Cu2O (s) + O2 (g) , what is D S ° at 298 K (in J/K) ? S ° [CuO] = 43 J/mol × K; S ° [O2] = 205 J/mol × K; S ° [Cu2O] = 93.14 J/mol × K

Which of the following chemical equations would be expected to have a positive sign for D S system? I. NaClO3 (s) →Na+ (aq) + ClO31 - (aq) II. NH3 (g) + HBr (g) →NH4Br (s) III. H2S (g) + 1/2 O 2 (g) →1/8 S8 (s) + H2O (g)

Which process below is accompanied by a decrease in entropy for the system ?

Which of the following reactions would be expected to have a positive entropy change , D S > 0? I. 3 O2 (g) →2 O3 (g) II. CaCO3 (s) →CaO (s) + CO2 (g) III. C3H8 (g) + 5 O2 (g) →3 CO2 (g) + 4 H2O (g)

Which of the following physical changes would be expected to provide a positive change in entropy , D S > 0? I. Compressing a gas until it liquefies. II. Melting an ice-cube. III. Heating a substance to a higher temperature.

Using the entropy values in the table below, what is the change in standard entropy, D S , for the following reaction? 2 CH₃ OH (g) + 3 O₂(g) 2 CO₂ (g) + 4 H₂ O (g) Substance S (J/mol K) CH₃ OH ( ) 126.8 CH₃ OH (g) 237.6 O₂(g) 205.0 CO₂ (g) 213.6 H₂ O (g) 188.83 H₂ O ( ) 69.91

"A spontaneous change is always accompanied by an increase in entropy." The entropy change referred to in this statement is:

Which of the following chemical reactions would be expected to have a positive sign for D S reaction? I. 2 N2 (g) + 3 F2 (g) →2 NF3 (g) II. NaCl (aq) + AgNO3 (aq) →NaNO3 (aq) + AgCl (s) III. CaCO3 (s) →CaO (s) + CO2 (g)

Which of the following reactions would be expected to provide a negative change in entropy , D S I. 2 K (s) + F2 (g) →2 KF (s) II. 2 NO2 (g) →N2O4 (g) III. NaClO3 (s) →Na+ (aq) + ClO31 - (aq)

Which of the following chemical reactions has the largest positive entropy change?

Which of the following processes would be expected to have a positive sign for D S system? I. Hot air expanding. II. A piece of wax melting. III. Alcohol evaporating.

The entropy change when one mole of acetone [(CH3) 2CO] vaporizes at its boiling point (56 ° C) is D S vap = 97.16 J/mol × K. How much heat is absorbed when 58.0 grams of acetone vaporizes at 56 ° C?

Which of the following reactions would be expected to have a positive entropy change, D S 0? I. 2 SO₂ (g) + O₂(g) 2 SO3(g) II. Ba(OH) 2 (s) BaO (s) + H₂ O (g) III. CO (g) + 2 H₂ (g) CH₃ OH ( )

Which of the following processes results in a negative entropy change?

Estimate the normal boiling point of mercury, given that for Hg ( ) , = 0 kJ/mol and D S = 76.02 J/mol K and for Hg (g) , = 61.32 kJ/mol and D S = 174.85 J/mol K. The change is: Hg ( ) Hg (g)

For which of the following processes will D S _system be the most positive?

Which of the following physical changes would be expected to have a negative sign for D S _system? I. Dissolving oxygen gas, O₂, in water. II. Freezing ice cubes. III. Breaking glass.

For the reaction 4 CuO (s) →2 Cu₂O (s) + O₂ (g) , what is D S ° at 298 K (in J/K) ? S ° [CuO] = 43 J/mol × K; S ° [O₂] = 205 J/mol × K; S ° [Cu₂O] = 93.14 J/mol × K

Which of the following chemical equations would be expected to have a positive sign for D S _system? I. NaClO₃ (s) →Na⁺ (aq) + ClO₃^{1 -} (aq) II. NH₃ (g) + HBr (g) →NH₄Br (s) III. H₂S (g) + ¹/₂ O₂ (g) →¹/₈ S₈ (s) + H₂O (g)

Which of the following reactions would be expected to have a positive entropy change , D S > 0? I. 3 O₂ (g) →2 O₃ (g) II. CaCO₃ (s) →CaO (s) + CO₂ (g) III. C₃H₈ (g) + 5 O₂ (g) →3 CO₂ (g) + 4 H₂O (g)

Which of the following chemical reactions would be expected to have a positive sign for D S _reaction? I. 2 N₂ (g) + 3 F₂ (g) →2 NF₃ (g) II. NaCl (aq) + AgNO₃ (aq) →NaNO₃ (aq) + AgCl (s) III. CaCO₃ (s) →CaO (s) + CO₂ (g)

Which of the following reactions would be expected to provide a negative change in entropy , D S I. 2 K (s) + F₂ (g) →2 KF (s) II. 2 NO₂ (g) →N₂O₄ (g) III. NaClO₃ (s) →Na⁺ (aq) + ClO₃^{1 -} (aq)

Which of the following processes would be expected to have a positive sign for D S _system? I. Hot air expanding. II. A piece of wax melting. III. Alcohol evaporating.

The entropy change when one mole of acetone [(CH₃) ₂CO] vaporizes at its boiling point (56 ° C) is D S _vap = 97.16 J/mol × K. How much heat is absorbed when 58.0 grams of acetone vaporizes at 56 ° C?

Which of the following reactions would be expected to have a positive entropy change, D S 0? I. 2 SO₂ (g) + O₂(g) 2 SO₃(g) II. Ba(OH) 2 (s) BaO (s) + H₂ O (g) III. CO (g) + 2 H₂ (g) CH₃ OH ( )