Deck 10: Entropy and the Second Law of Thermodynamics

Question 1

If a 5.0 L flask holds 0.125 moles of nitrogen at STP, what happens to the entropy of the system upon cooling the gas to -75 °C?

A)The entropy increases.
B)The entropy remains the same.
C)The entropy decreases.
D)There is too little information to assess the change.

Answer 1

The entropy decreases.

Question 2

Which process is the best example of a spontaneous process?

A)At STP, nitrogen and oxygen react to form nitrogen monoxide.
B)C(graphite)turns to C(diamond).
C)Hydrogen and oxygen react to form water.
D)At STP, carbon dioxide and water react to form carbonic acid.

Answer 2

Hydrogen and oxygen react to form water.

Question 3

Just because a process is spontaneous, it may not happen quickly.

Answer 3

True

Question 4

The entropy of a perfect crystal of any pure substance approaches zero when:

A)it reacts with a halogen gas.
B)the system surpasses the boiling point of its highest boiling component.
C)the temperature of the system approaches absolute zero.

Question 5

The entropy of a system decreases as the system moves toward more random distributions of the particles it contains.

Question 6

All exothermic processes are spontaneous

Question 7

Exothermic reactions with negative values of S ° are spontaneous at all temperatures.

Question 8

Without detailed calculations, predict the sign of Δ S for the following reaction: ​
Mg( s )+ O₂( g )→ MgO( s )

A)Positive (+)
B)Negative ( − )
C)Zero
D)Too little information to assess the change

Question 9

Converting heat into work decreases entropy because the random motions of molecules become more ordered as a result of the directional aspect of work.

Question 10

The randomness of a system may be described as _____.

A)enthalpy
B)entropy
C)kinetic energy
D)Gibbs free energy

Question 11

Entropy is a state function.

Question 12

According to the second law of thermodynamics, the entropy of the universe must ____ for a spontaneous process.

A)increase
B)remain the same
C)decrease

Question 13

Average PET chain lengths tend to shorten during the recycling process.

Question 14

All reactions with a positive Δ S ° are spontaneous regardless of temperature.

Question 15

Processes that are spontaneous only at lower temperatures are sometimes said to be enthalpy driven.

Question 16

In most cases, during the synthesis of a polymer:

A)the entropy increases.
B)the entropy remains the same.
C)the entropy decreases.
D)there is too little information to assess the change.

Question 17

At which of the following temperatures is the entropy of a water sample the highest?

A)− 15 ° C
B)2 ° C
C)99 ° C
D)135 ° C

Question 18

The use of recycled PET to make drink bottles is more cost effective than using virgin PET.

Question 19

A reaction with a _____ is spontaneous at all temperatures.

A)negative Δ H and a positive Δ S
B)positive Δ H and a negative Δ S
C)positive Δ H and Δ S
D)negative Δ H and Δ S

Question 20

Two 6.5 L flasks are joined by a 150 mL tube with a stopcock. If 0.25 moles of nitrogen is held in the left flask and the right flask is empty, what would happen to the entropy of the system upon opening the valve between the flasks?

A)The entropy would increase.
B)The entropy would remain the same.
C)The entropy would decrease.
D)There is too little information to assess the change.

Question 21

Consider the following reaction for the combustion of ethane (C ₂ H ₆ ): ​
C₂H₆( g )+ O₂( g )→ CO₂( g )+ H₂O( l ).
​
If Δ G ° (in kJ\moles)for C ₂ H ₆ ( g )is − 32.9, for O ₂ ( g )is 0, for CO ₂ ( g )is − 394.4, and for H ₂ O( l )is − 237.2; calculate Δ G ° for the reaction.

A)− 2146.2 kJ
B)− 2935.0 kJ
C)+2146.2 kJ
D)− 598.7 kJ

Question 22

The second law of thermodynamics states that in any spontaneous process, the total entropy change of the universe is positive.

Question 23

When magnesium sulfite decomposes, the solid transforms into magnesium oxide and sulfur dioxide. The reaction is as follows:
MgSO ₃ ( s )→ MgO( s )+ SO ₂ ( g )
According to the Gibbs free energy, at what temperature will this reaction be spontaneous?
Δ G in kJ\moles for MgSO ₃ ( s )is − 1172, for MgO( s )is − 569.6, and for SO ₂ ( g )is − 300.2. Δ H in kJ\moles for MgSO ₃ ( s )is − 1068, for MgO( s )is − 601.8, and for SO ₂ ( g )is − 296.8. Δ S in J\moles K for MgSO ₃ ( s )is 121, for MgO( s )is 27, and for SO ₂ ( g )is 248.1.

A)At temperatures below − 63.1 K
B)At temperatures below 179.5 K
C)At temperatures below 415.8 K
D)At temperatures above 1100 K

Question 24

Calculate Δ G° for the following reaction:
2 NO ₂ ( g )→ N ₂ ( g )+ 2 O ₂ ( g ).
Δ G _f ° in kJ\moles for NO ₂ ( g )is 51.30.

A)+51.3  kJ
B)− 51.3  kJ
C)+103  kJ
D)− 103  kJ

Question 25

Calculate Δ G° for the following reaction: ​
SO₃( g )+ CaO( s )→ CaSO₄( s ).
​
Δ G _f ° in kJ\moles for CaO( s )is − 604.2, for SO ₃ ( g )is − 371.1, and for CaSO ₄ ( s )is − 1320.

A)− 2230  kJ
B)− 345  kJ
C)− 323  kJ
D)+189  kJ

Question 26

Calculate Δ S° for the following reaction: ​
2 SO₃( g )→ 2 SO₂( g )+ O₂( g ).
​
Δ S° in J\moles K for SO ₂ ( g )is 248.1, for SO ₃ ( g )is 256.6, and for O ₂ ( g )is 205.0.

A)− 537 J\moles K
B)+188 J\moles K
C)− 188 J\molesK
D)+537 J\moles K

Question 27

What is the melting point of polyvinyl chloride if the heat of fusion of crystalline polyvinyl chloride is approximately 11.0 kJ\moles, and the corresponding entropy change for melting is 68.75 J moles ^{− 1} K ^{− 1} ?

A)120 K
B)160 K
C)200 K
D)240 K

Question 28

In the context of free energy and work, the amount of work available in an irreversible change is always less than
the maximum work.

Question 29

Calculate Δ G° for the following reaction: ​
2 SO₃( g )→ 2 SO₂( g )+ O₂( g )
​
Δ G _f ° in kJ\moles for SO ₂ ( g )is − 300.2, and for SO ₃ ( g )is − 371.1.

A)− 141.8  kJ
B)+70.9  kJ
C)− 70.9  kJ
D)+141.8  kJ

Question 30

Which of the following is an example of a state function?

A)Temperature
B)Heat
C)Work
D)Displacement

Question 31

Calculate Δ S° for the following reaction: ​
SO₃( g )+ CaO( s )→ CaSO₄( s ).
​
Δ S° in J\moles K for CaO( s )is 40, for SO ₃ ( g )is 256.6, and for CaSO ₄ ( s )is 107.

A)+404 J\K
B)− 190 J\K
C)− 323 J\K
D)+189 J\K

Question 32

The degradation of phosgene (COCl ₂ )into CO and Cl ₂ is not spontaneous at room temperature and standard state conditions (273 K, 1 atm). Which of the following can make this a spontaneous reaction?

A)Increasing the temperature
B)Decreasing the temperature
C)Adding CO to COCl ₂
D)Adding Cl ₂ to COCl ₂

Question 33

A reaction that has a positive Δ H and a negative Δ S is spontaneous at all temperatures.

Question 34

Calculate Δ S° for the following reaction:
2 NO ₂ ( g )→ N ₂ ( g )+ 2 O ₂ ( g ).
Δ S° in J\moles K for NO ₂ ( g )is 240.0, for N ₂ ( g )is 191.5, and for O ₂ ( g )is 205.0.

A)+157 J\K
B)− 102.8 J\K
C)+121.5 J\K
D)− 480 J\K

Question 35

Consider the following reaction of carbon monoxide with oxygen to produce carbon dioxide. ​
2 CO( g )+ O₂( g )→ 2 CO₂( g )
​
At what temperature will this reaction be spontaneous according to Gibbs free energy?
​
Δ H in kJ\moles for CO( g )is − 110.5 and for CO ₂ ( g )is − 393.5. Δ S in J\moles K for CO( g )is 197.6, and for CO ₂ ( g )is 213.6, O ₂ ( g )= 205.0.

A)At temperatures above − 63.1 K
B)At temperatures below 179.5 K
C)At temperatures above 415.8 K
D)At temperatures below 3272 K