Question 1

The standard entropy for the formation of sulfur hexafluoride from the sulfur and fluorine is -348.7 J/K ⋅mol-rxn at 298.15 K.What is the standard molar entropy of sulfur hexafluoride for the reaction below? (Given: S°[S(s)] = 32.1 J/K ⋅mol and S°[F2(g)] = 202.8 J/K ⋅mol)
A) -988.6 J/K⋅mol
B) +291.8 J/K⋅mol
C) -291.8 J/K⋅mol
D) -113.2 J/K⋅mol
E) +113.8 J/K⋅mol

Accepted Answer

The standard molar entropy of sulfur hexafluoride (SF6) can be calculated using the given standard entropies and the standard entropy change for the reaction. The reaction is:$$ S(s) + 3F_2(g) \rightarrow SF_6(g) $$The standard entropy change ($\Delta S^\circ$) for the reaction is given as -348.7 J/K⋅mol. The standard molar entropies of sulfur (S°[S(s)]) and fluorine (S°[F2(g)]) are given as 32.1 J/K⋅mol and 202.8 J/K⋅mol, respectively. To find the standard molar entropy of SF6 (S°[SF6(g)]), we can rearrange the equation for the standard entropy change of the reaction:$$ \Delta S^\circ = S^\circ_{products} - S^\circ_{reactants} $$$$ -348.7 = S^\circ[SF_6] - (S^\circ[S(s)] + 3 \times S^\circ[F_2(g)]) $$$$ -348.7 = S^\circ[SF_6] - (32.1 + 3 \times 202.8) $$$$ -348.7 = S^\circ[SF_6] - (32.1 + 608.4) $$$$ -348.7 = S^\circ[SF_6] - 640.5 $$$$ S^\circ[SF_6] = 640.5 - 348.7 $$$$ S^\circ[SF_6] = 291.8 \, J/K \cdot mol $$Therefore, the standard molar entropy of sulfur hexafluoride is +291.8 J/K⋅mol.

Question 2

In which of the following reactions is Δ_rS° expected to be positive? A) 2C₂H₆(g)+ 7O₂(g)→ 4CO₂(g)+ 6H₂O(l) B) Ga(l)→ Ga(s) C) H₂O(l)+ 2SO₂(g)→ H₂SO₄(l) D) CO₂(g)→ CO₂(s) E) None of these

Accepted Answer

In all given reactions, the number of gas molecules decreases or a phase change to a more ordered state occurs, leading to a decrease in entropy (ΔS° negative).

Question 3

What is the standard entropy change for the following reaction? 4 N₂(g) + 12 H₂(g) → 8 NH₃(g) (J/mol⋅K) 191)5 130)6 192)3 A) -794.8 J/K⋅mol-rxn B) 794.8 J/K⋅mol-rxn C) 2948.8 J/K⋅mol-rxn D) -2948.8 J/K⋅mol-rxn E) -129.8 J/K⋅mol-rxn

Accepted Answer

A

Question 4

Which of the following is the third law of thermodynamics as defined by Ludwig Boltzmann?
A) A perfect crystal at 0 K has zero entropy.
B) In a spontaneous process,the entropy of the universe increases.
C) The total entropy of the universe is always increasing.
D) The total mass of the universe is constant.
E) Mass and energy are conserved in all chemical reactions.

Accepted Answer

The third law of thermodynamics, as defined by Ludwig Boltzmann, states that a perfect crystal at 0 Kelvin (absolute zero) has zero entropy.

Question 5

For a certain reversible process,q = 88.06 kJ at 29.4°C.Which of the following is the ΔS for the process?
A) 0.291 J/K
B) 291 J/K
C) 3.00 J/K
D) -0.291 J/K
E) 2590 J/K

Accepted Answer

The change in entropy (ΔS) for a reversible process can be calculated using the formula ΔS = q/T, where q is the heat exchanged and T is the temperature in Kelvin. To convert 29.4°C to Kelvin, add 273.15 to get 302.55 K. Then, ΔS = 88.06 kJ / 302.55 K = 0.291 kJ/K = 291 J/K, since 1 kJ = 1000 J.

Question 6

Which of the following is the second law of thermodynamics?
A) In a spontaneous process,the entropy of the universe increases.
B) There is no disorder in a perfect crystal at 0 K.
C) The total energy of the universe is always increasing.
D) The total energy of the universe is constant.
E) Mass and energy are conserved in all chemical reactions.

Accepted Answer

The second law of thermodynamics states that in a spontaneous process, the entropy of the universe always increases. Entropy is a measure of the disorder or randomness of a system, and the second law tells us that the total amount of disorder or randomness in the universe is always increasing. Choice B is not a statement of the second law and refers to a specific scenario of a perfect crystal at 0 K, which is not representative of most systems. Choice C is not true since energy can be converted from one form to another, but it cannot be created or destroyed. Choice D is a statement of the first law of thermodynamics and not the second law. Choice E refers to the conservation of mass and energy, which is also not a statement of the second law.

Question 7

Calculate the standard entropy change for the following reaction: 2 SO₂(g)+ O₂(g)→ 2 SO₃(g) Given: S°[SO₂(g)] = 248.2 J/K⋅mol,S°[O₂(g)] = 205.1 J/K⋅mol,and S°[SO₃(g)] = 256.8 J/K⋅mol. A) -196.5 J/K·mol-rxn B) -94.0 J/K·mol-rxn C) -187.9 J/K·mol-rxn D) +187.9 J/K·mol-rxn E) +196.5 J/K·mol-rxn

Accepted Answer

ΔS°rxn = ΣS°(products) - ΣS°(reactants) ΔS°rxn = [2 × S°(SO₃(g))] - [2 × S°(SO₂(g))] - [S°(O₂(g))] ΔS°rxn = [2 × 256.8 J/K·mol] - [2 × 248.2 J/K·mol] - [205.1 J/K·mol] ΔS°rxn = -187.9 J/K·mol-rxn Therefore, the correct answer is C, as it matches the calculated value for the standard entropy change of the reaction.

Question 8

Which of the following represents the change in entropy for a system going from 142 possible microstates to 830 possible microstates? (k = 1.381 × 10^-23 J/K) A) J/K B) J/K C) − J/K D) J/K E) − J/K

Accepted Answer

The change in entropy can be calculated using the equation ΔS = k ln(W2/W1), where k is the Boltzmann constant, ln is the natural logarithm, W1 is the initial number of microstates, and W2 is the final number of microstates.

Plugging in the values given:
ΔS = (1.381 × 10-23 J/K) ln(830/142)
ΔS ≈ 1.65 × 10-22 J/K

Converting the value to scientific notation: 
ΔS ≈ 1.65e-22 J/K

Therefore, the correct choice is D, 11eac9a9_4b86_c1c1_acc3_5d862f17561d_TB7480_11 J/K.

Question 9

Which of the following compounds has the highest standard entropy per mole at 298 K? A) H₂O(l) B) CaCO₃(s) C) CO(g) D) SiO₂(s) E) CH₃OH(l)

Accepted Answer

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is zero. Since CO in gaseous form has the most disorder and is farthest from a perfect crystal, it has the highest standard entropy per mole at 298 K.

Question 10

If a chemical reaction occurs in a direction that has a positive change in entropy,then _____.
A) the change in enthalpy must be negative.
B) the reaction must be spontaneous.
C) the heat goes from the system into the surroundings.
D) the reaction must be exothermic.
E) the disorder of the system increases.

Accepted Answer

A positive change in entropy indicates an increase in the disorder or randomness of the system, which is what option E states. The other options are not necessarily true based on the information given about entropy.

Question 11

Which of the following linear chain alcohols is likely to have the highest standard entropy in the liquid state? A) CH₃OH B) CH₃CH₂OH C) CH₃CH₂CH₂OH D) CH₃CH₂CH₂CH₂OH E) CH₃CH₂CH₂CH₂CH₂OH

Accepted Answer

Entropy generally increases with molecular complexity and size because larger molecules have more vibrational modes and thus more ways to distribute energy. Option E represents the longest linear chain alcohol, implying it has the highest standard entropy in the liquid state due to its increased molecular complexity and size.

Question 12

Which of the following changes lead to a decrease in entropy?
A) Sugar dissolving in coffee
B) Diffusion of perfume throughout a room
C) Evaporation of gasoline
D) The sublimation (vaporization)of dry ice (solid carbon dioxide)
E) Condensation of steam on glass

Accepted Answer

Condensation of steam on glass leads to a decrease in entropy because the gas phase (steam) has higher entropy than the liquid phase (condensed water droplets) on the surface of the glass.

Question 13

Which of the following is true of the deposition of a gaseous substance? A) ΔS° = 0 and ΔH° = 0. B) ΔS° > 0 and ΔH° > 0. C) ΔS° < 0 and ΔH° > 0. D) ΔS° < 0 and ΔH° < 0. E) ΔS° > 0 and ΔH° < 0.

Accepted Answer

The deposition of a gaseous substance involves a phase change from gas to solid. This process is characterized by a decrease in entropy (ΔS° < 0) as the gas molecules become more ordered in a solid state. The process is exothermic, meaning heat is released (ΔH° < 0) as the gas molecules lose energy and bond together to form a solid. Therefore, the correct answer is option D.

Question 14

For which of the following reactions will the entropy of a system decrease? A) 2 NH₃(g)→ N₂(g)+ 3 H₂(g) B) 2 C(s)+ O₂(g)→ 2 CO(g) C) CaCO₃(s)→ CaO(s)+ CO₂(g) D) 2 NO₂(g)→ N₂O₄(g) E) NaOH(s)→ Na⁺(aq)+ OH^-(aq)

Accepted Answer

The reaction D involves the combination of two gas molecules into one, reducing the number of gas particles and thus decreasing the entropy of the system.

Question 15

What is the S0 for ozone if the standard entropy change for the reaction below is 411 J/K⋅mol-rxn and S⁰[O₂(g)] = 205 J/K⋅mol. 6 O₃(g)→ 9 O₂(g) A) 364 J/K⋅mol-rxn B) 478 J/K⋅mol-rxn C) 239 J/K⋅mol-rxn D) −117 J/K⋅mol-rxn E) −59 J/K⋅mol-rxn

Accepted Answer

We can use the equation ΔS°rxn = ΣS°(products) - ΣS°(reactants) and the given standard entropies to solve for the standard entropy of ozone, S°(O3).

ΔS°rxn = (9 mol x S°(O2)) - (6 mol x S°(O3))

411 J/K⋅mol = (9 mol x 205 J/K⋅mol) - (6 mol x S°(O3))

S°(O3) = -239 J/K⋅mol

Note that the negative sign indicates that the entropy of ozone is less than that of the standard state.

Question 16

For the reaction Br₂(l)→ 2Br(g),_____. A) ΔH is + and ΔS is + B) ΔH is + and ΔS = 0 C) ΔH is - and ΔS is - D) ΔH is - and ΔS is + E) ΔH is + and ΔS is -

Accepted Answer

The reaction involves the conversion of a liquid to a gas, which requires energy (endothermic, ΔH is +) and increases disorder (ΔS is +).

Question 17

Which of the following statements concerning entropy is not correct?
A) The entropy of a system increases as the number of available microstates increases.
B) The entropy of a system is proportional to the natural log of the number of microstates.
C) In a spontaneous process,ΔS(universe)indicates the extent to which energy is dispersed.
D) The dispersal of matter,such as the spontaneous expansion of a gas,cannot be explained by an increase in entropy.
E) Entropy is a measure of the extent of energy dispersal.

Accepted Answer

The statement "The dispersal of matter,such as the spontaneous expansion of a gas,cannot be explained by an increase in entropy" is not correct. The spontaneous expansion of a gas is a clear example of an increase in entropy, as the number of available microstates (positions and velocities of gas molecules) increases. Thus, the correct statement should be that the dispersal of matter, such as the spontaneous expansion of a gas, is an example of an increase in entropy.

Question 18

Which of the following is the first law of thermodynamics?
A) In a spontaneous process,the entropy of the universe increases.
B) There is no disorder in a perfect crystal at 0 K.
C) The total energy of the universe is always decreasing.
D) Energy cannot be created or destroyed.
E) mass and energy are conserved in all chemical reactions.

Accepted Answer

The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another.

Question 19

What is the sign of ΔH (system)and ΔS (system)if a chemical reaction is spontaneous only at lower temperatures under standard conditions?
A) ΔH (system)is negative,and ΔS (system)is negative.
B) ΔH (system)is positive,and ΔS (system)is positive.
C) ΔH (system)is positive,and ΔS (system)is negative.
D) ΔH (system)is negative,and ΔS (system)is positive.
E) None of these

Accepted Answer

For a reaction to be spontaneous at lower temperatures, ΔH must be negative (exothermic) and ΔS must be negative (decrease in entropy). This ensures that the negative ΔH term dominates the Gibbs free energy equation (ΔG = ΔH - TΔS) at lower temperatures, making ΔG negative and the reaction spontaneous.

Question 20

Calculate ΔS°(universe)for the combustion of acetylene at 298.15 K using the reaction below.(Given: ΔS°(system)= -194.6 J/K and ΔH°(system)= -2511.2 kJ) 2 C₂H₂(g)+ 5 O₂(g)→ 4 CO₂(g)+ 2 H₂O(g) A) -2453.2 J/K B) -186.2 J/K C) +186.2 J/K D) +1290.4 J/K E) +8228.0 J/K

Accepted Answer

The answer of Calculate ΔS°(universe)for the combustion of acetylene at...

Quiz 19: Principles of Chemical Reactivity: Entropy and Free Energy

The standard entropy for the formation of sulfur hexafluoride from the sulfur and fluorine is -348.7 J/K ⋅mol-rxn at 298.15 K.What is the standard molar entropy of sulfur hexafluoride for the reaction below? (Given: S°[S(s) ] = 32.1 J/K ⋅mol and S°[F2(g) ] = 202.8 J/K ⋅mol)

In which of the following reactions is Δ_rS° expected to be positive?

What is the standard entropy change for the following reaction? 4 N₂(g) + 12 H₂(g) → 8 NH₃(g) (J/mol⋅K) 191) 5 130) 6 192) 3

Which of the following is the third law of thermodynamics as defined by Ludwig Boltzmann?

For a certain reversible process,q = 88.06 kJ at 29.4°C.Which of the following is the ΔS for the process?

Which of the following is the second law of thermodynamics?

Calculate the standard entropy change for the following reaction: 2 SO₂(g) + O₂(g) → 2 SO₃(g) Given: S°[SO₂(g) ] = 248.2 J/K⋅mol,S°[O₂(g) ] = 205.1 J/K⋅mol,and S°[SO₃(g) ] = 256.8 J/K⋅mol.

Which of the following represents the change in entropy for a system going from 142 possible microstates to 830 possible microstates? (k = 1.381 × 10^-23 J/K)

Which of the following compounds has the highest standard entropy per mole at 298 K?

If a chemical reaction occurs in a direction that has a positive change in entropy,then _____.

Which of the following linear chain alcohols is likely to have the highest standard entropy in the liquid state?

Which of the following changes lead to a decrease in entropy?

Which of the following is true of the deposition of a gaseous substance?

For which of the following reactions will the entropy of a system decrease?

What is the S0 for ozone if the standard entropy change for the reaction below is 411 J/K⋅mol-rxn and S⁰[O₂(g) ] = 205 J/K⋅mol. 6 O₃(g) → 9 O₂(g)

For the reaction Br₂(l) → 2Br(g) ,_____.

Which of the following statements concerning entropy is not correct?

Which of the following is the first law of thermodynamics?

What is the sign of ΔH (system) and ΔS (system) if a chemical reaction is spontaneous only at lower temperatures under standard conditions?

Calculate ΔS°(universe) for the combustion of acetylene at 298.15 K using the reaction below.(Given: ΔS°(system) = -194.6 J/K and ΔH°(system) = -2511.2 kJ) 2 C₂H₂(g) + 5 O₂(g) → 4 CO₂(g) + 2 H₂O(g)