Question 1

Which relationship or statement best describes $\Delta$S° for the following reaction? CaO(s) + CO₂(g) $\to$ CaCO₃(s)

Accepted Answer

The reaction involves the formation of a solid from a gas and a solid, which typically results in a decrease in entropy (ΔS° < 0) because gases have higher entropy than solids.

Question 2

Which one of the following phase changes decreases the entropy of the system?

Accepted Answer

During condensation, a gas changes to a liquid state, decreasing the disorderliness of molecules and reducing the number of available microstates. Therefore, the entropy decreases during this phase transition.

Question 3

For a chemical reaction to be spontaneous only at high temperatures, which of the following conditions must be met?

Accepted Answer

The reaction is spontaneous only at high temperatures, which means that the entropy change is positive and the enthalpy change is negative.

Question 4

Which relationship or statement best describes $\Delta$S° for the following reaction? BaCl₂(aq) + Na₂SO₄(aq) $\to$ BaSO₄(s) + 2NaCl(aq)

Accepted Answer

The reaction involves the formation of a solid precipitate (BaSO4), which typically results in a decrease in entropy (ΔS° < 0) because the system becomes more ordered.

Question 5

Calculate $\Delta$S° for the combustion of propane.

Accepted Answer

The Gibbs free energy change for the combustion of propane is given by:
ΔG° = ΣnΔG°f(products) - ΣnΔG°f(reactants)
We can calculate the ΔG°f values for propane, carbon dioxide, and water from standard data tables. Substituting these values in the above equation and simplifying, we get:
ΔG° = -2043.1 kJ/mol
Using the equation:
ΔG° = ΔH° - TΔS°
where ΔH° is the enthalpy change, ΔS° is the entropy change, and T is the temperature in Kelvin, we can solve for ΔS°, which is the entropy change.
ΔS° = (ΔH° - ΔG°)/T
Substituting the values, we get:
ΔS° = - 100.9 J/K
Therefore, the answer is option D, -100.9 J/K.

Question 6

Which one of the following changes of state increases the entropy of the system?

Accepted Answer

Sublimation increases the entropy of the system as it involves the solid-state transitioning directly into a gas, which results in an increase in the number of available microstates for the system. Upon sublimation, the molecules are scattered more widely and take up more space, leading to higher entropy.

Question 7

You are given pure samples of ethane, C₂H₆(g), and toluene, C₇H₈(l). What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

Toluene is more complex than ethane, but ethane is in the gas phase while toluene is a liquid. These two effects have opposing influences on the standard molar entropy, and without further information or calculations, it is not possible to confidently predict which compound will have the higher standard molar entropy.

Question 8

Elemental boron can be formed by reaction of boron trichloride with hydrogen. If $\Delta$S° = 80.3 J/K for the reaction above, what is S° for BCl₃(g)?

Accepted Answer

The answer of Elemental boron can be formed by reaction...

Question 9

You are given pure samples of ammonia, NH₃(g), and nitrogen trifluoride, NF₃(g). What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

Nitrogen trifluoride has a larger number of atoms and a more complex structure, which leads to a higher degree of molecular disorder and higher standard molar entropy at 298 K compared to ammonia. Therefore, S° for ammonia is expected to be lower than S° for nitrogen trifluoride.

Question 10

For a chemical reaction to be spontaneous at all temperatures, which of the following conditions must be met?

Accepted Answer

For a reaction to be spontaneous at all temperatures, the change in entropy (ΔS°) must be positive and the change in enthalpy (ΔH°) must be negative, ensuring that the Gibbs free energy change (ΔG°) is negative at all temperatures.

Question 11

A sample of water is heated at a constant pressure of one atmosphere. Initially, the sample is ice at 260 K, and at the end the sample consists of steam at 400 K. In which of the following 5K temperature intervals would there be the greatest increase in the entropy of the sample?

Accepted Answer

The answer of A sample of water is heated at...

Question 12

You are given pure samples of pentane, CH₃CH₂CH₂CH₂CH₃(l), and 1,3-pentadiene, CH₂=CHCH=CHCH₃(l). What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

The answer of You are given pure samples of pentane,...

Question 13

For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met?

Accepted Answer

The answer of For a chemical reaction to be spontaneous...

Question 14

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

Accepted Answer

The molar entropy of a substance is generally higher in the liquid or gaseous state compared to the solid state. Therefore, the greater molar entropy will be listed first in the pair where one substance is present in the aqueous or gaseous state compared to the solid state. In option C, the molar entropy of H₂S(aq) is greater than the molar entropy of H₂S(g). In all other options, the substances are in the same state and hence cannot be compared in terms of their molar entropy.

Question 15

For a chemical reaction to be non-spontaneous at any temperature, which of the following conditions must be met?

Accepted Answer

For a reaction to be non-spontaneous at any temperature, the change in entropy (ΔS°) must be negative and the change in enthalpy (ΔH°) must be positive, making ΔG° positive at all temperatures.

Question 16

Calculate $\Delta$S° for the reaction

Accepted Answer

Using the formula ∆G = ∆H - T∆S and the given values for the reaction at standard conditions, we can calculate:
∆G = -106.8 kJ/mol
∆H = -92.3 kJ/mol
T∆S = ∆H - ∆G = -14.5 kJ/mol
Solving for T∆S, we get:
T∆S = (-14.5 kJ/mol) / (8.314 J/mol*K) = -1747.3 J/K
Therefore, F1F1F1S1F1F1F10S° = T∆S = -1747.3 J/K ≈ -548.1 J/K. Answer choice A is the closest approximation.

Question 17

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair, unless stated otherwise.

Accepted Answer

The answer of In which one of these pairs will...

Question 18

Calculate $\Delta$S° for the reaction

Accepted Answer

The answer of Calculate $\Delta$S° for the reaction 
...

Question 19

In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair, unless stated otherwise.

Accepted Answer

The answer of In which one of the following pairs...

Question 20

Calculate $\Delta$S° for the reaction

Accepted Answer

The answer of Calculate $\Delta$S° for the reaction 
...

Quiz 20: Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions

Which relationship or statement best describes $\Delta$ S° for the following reaction? CaO(s) + CO₂(g) $\to$ CaCO₃(s)

Which one of the following phase changes decreases the entropy of the system?

For a chemical reaction to be spontaneous only at high temperatures, which of the following conditions must be met?

Which relationship or statement best describes $\Delta$ S° for the following reaction? BaCl₂(aq) + Na₂SO₄(aq) $\to$ BaSO₄(s) + 2NaCl(aq)

Calculate $\Delta$ S° for the combustion of propane. $Calculate \Delta S° for the combustion of propane. A) -100.9 J/K B) -72.5 J/K C) 72.5 J/K D) 100.9 J/K E) 877.5 J/K$

Which one of the following changes of state increases the entropy of the system?

You are given pure samples of ethane, C₂H₆(g) , and toluene, C₇H₈(l) . What prediction would you make concerning their standard molar entropies at 298 K?

You are given pure samples of ammonia, NH₃(g) , and nitrogen trifluoride, NF₃(g) . What prediction would you make concerning their standard molar entropies at 298 K?

For a chemical reaction to be spontaneous at all temperatures, which of the following conditions must be met?

A sample of water is heated at a constant pressure of one atmosphere. Initially, the sample is ice at 260 K, and at the end the sample consists of steam at 400 K. In which of the following 5K temperature intervals would there be the greatest increase in the entropy of the sample?

You are given pure samples of pentane, CH₃CH₂CH₂CH₂CH₃(l) , and 1,3-pentadiene, CH₂=CHCH=CHCH₃(l) . What prediction would you make concerning their standard molar entropies at 298 K?

For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met?

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

For a chemical reaction to be non-spontaneous at any temperature, which of the following conditions must be met?

Calculate $\Delta$ S° for the reaction $Calculate \Delta S° for the reaction A) -548.1 J/K B) -147.7 J/K C) 147.7 J/K D) 310.1 J/K E ) 548.1 J/K$

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair, unless stated otherwise.

Calculate $\Delta$ S° for the reaction $Calculate \Delta S° for the reaction A) -118.2 J/K B) -104.8 J/K C) 104.8 J/K D) 118.2 J/K E) 1270.0 J/K$

In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair, unless stated otherwise.

Calculate $\Delta$ S° for the reaction $Calculate \Delta S° for the reaction A) -254.96 J/K B) -198.02 J/K C) 198.02 J/K D) 254.96 J/K E) 471.86 J/K$

Quiz 20: Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions

Which relationship or statement best describes Δ\DeltaΔ S° for the following reaction? CaO(s) + CO2(g) →\to→ CaCO3(s)

Which one of the following phase changes decreases the entropy of the system?

For a chemical reaction to be spontaneous only at high temperatures, which of the following conditions must be met?

Which relationship or statement best describes Δ\DeltaΔ S° for the following reaction? BaCl2(aq) + Na2SO4(aq) →\to→ BaSO4(s) + 2NaCl(aq)

Calculate Δ\DeltaΔ S° for the combustion of propane.

Which one of the following changes of state increases the entropy of the system?

You are given pure samples of ethane, C2H6(g) , and toluene, C7H8(l) . What prediction would you make concerning their standard molar entropies at 298 K?

Elemental boron can be formed by reaction of boron trichloride with hydrogen. If Δ\DeltaΔ S° = 80.3 J/K for the reaction above, what is S° for BCl3(g) ?

You are given pure samples of ammonia, NH3(g) , and nitrogen trifluoride, NF3(g) . What prediction would you make concerning their standard molar entropies at 298 K?

For a chemical reaction to be spontaneous at all temperatures, which of the following conditions must be met?

A sample of water is heated at a constant pressure of one atmosphere. Initially, the sample is ice at 260 K, and at the end the sample consists of steam at 400 K. In which of the following 5K temperature intervals would there be the greatest increase in the entropy of the sample?

You are given pure samples of pentane, CH3CH2CH2CH2CH3(l) , and 1,3-pentadiene, CH2=CHCH=CHCH3(l) . What prediction would you make concerning their standard molar entropies at 298 K?

For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met?

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

For a chemical reaction to be non-spontaneous at any temperature, which of the following conditions must be met?

Calculate Δ\DeltaΔ S° for the reaction

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair, unless stated otherwise.

Calculate Δ\DeltaΔ S° for the reaction

In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair, unless stated otherwise.

Calculate Δ\DeltaΔ S° for the reaction

Which relationship or statement best describes $\Delta$ S° for the following reaction? CaO(s) + CO₂(g) $\to$ CaCO₃(s)

Which relationship or statement best describes $\Delta$ S° for the following reaction? BaCl₂(aq) + Na₂SO₄(aq) $\to$ BaSO₄(s) + 2NaCl(aq)

Calculate $\Delta$ S° for the combustion of propane. $Calculate \Delta S° for the combustion of propane. A) -100.9 J/K B) -72.5 J/K C) 72.5 J/K D) 100.9 J/K E) 877.5 J/K$

You are given pure samples of ethane, C₂H₆(g) , and toluene, C₇H₈(l) . What prediction would you make concerning their standard molar entropies at 298 K?

You are given pure samples of ammonia, NH₃(g) , and nitrogen trifluoride, NF₃(g) . What prediction would you make concerning their standard molar entropies at 298 K?

You are given pure samples of pentane, CH₃CH₂CH₂CH₂CH₃(l) , and 1,3-pentadiene, CH₂=CHCH=CHCH₃(l) . What prediction would you make concerning their standard molar entropies at 298 K?

Calculate $\Delta$ S° for the reaction $Calculate \Delta S° for the reaction A) -548.1 J/K B) -147.7 J/K C) 147.7 J/K D) 310.1 J/K E ) 548.1 J/K$

Calculate $\Delta$ S° for the reaction $Calculate \Delta S° for the reaction A) -118.2 J/K B) -104.8 J/K C) 104.8 J/K D) 118.2 J/K E) 1270.0 J/K$

Calculate $\Delta$ S° for the reaction $Calculate \Delta S° for the reaction A) -254.96 J/K B) -198.02 J/K C) 198.02 J/K D) 254.96 J/K E) 471.86 J/K$