Deck 10: Entropy and the Second Law of Thermodynamics

Question 1

Which process is the best example of a spontaneous process?

A) CO₂ and steam recombine to form an oak tree
B) C (graphite) turns to C (diamond)
C) hydrogen and oxygen react to form water
D) a dorm room cleans itself

Answer 1

hydrogen and oxygen react to form water

Question 2

At what temperature is the entropy of a water sample the highest?

A) − 15 ° C
B) 2 ° C
C) 99 ° C
D) 135 ° C

Answer 2

135 ° C

Question 3

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

Answer 3

True

Question 4

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.

Question 5

All exothermic processes are spontaneous

Question 6

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

Question 7

The use of recycled PET is more cost effective for soda pop bottling than using virgin PET.

Question 8

Consider the combustion of glucose (C₆H₁₂O₆). This reaction is:

A) spontaneous at all temperatures
B) non-spontaneous at all temperatures
C) spontaneous towards higher temperatures
D) non-spontaneous towards lower temperatures

Question 9

Processes that are spontaneous only at lower temperatures are referred to as enthalpy driven reactions.

Question 10

The entropy of a system decreases as it moves toward increasing random distributions of particles.

Question 11

Entropy is a state function.

Question 12

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

A) positive (+)
B) negative ( − )
C) zero
D) too little information to assess the change

Question 13

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

Question 14

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

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 15

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

Question 16

The randomness of a system may be described as its:

A) enthalpy
B) entropy
C) kinetic energy
D) Gibb's energy

Question 17

Which statement best describes the change in entropy 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 18

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 19

The entropy of a system approaches zero as:

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

Question 20

Just because a process is spontaneous does not mean that it happens quickly

Question 21

Consider the combustion of ethane (C₂H₆): ​
C₂H₆( g ) + O₂( g ) → CO₂( g ) + H₂O( l )
​
If Δ G ° (in kJ/mol) for: C₂H₆( g ) = − 32.9, O₂( g ) = 0, CO₂( g ) = − 394.4, and H₂O( l ) = − 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

Calculate Δ S for the reaction:
2 SO₃( g ) → 2 SO₂( g ) + O₂( g )
Δ S in J/mol K for: SO₂( g ) = 248.1, SO₃( g ) = 256.6, O₂( g ) = 205.0

A) − 537 J/mol K
B) +188 J/mol K
C) − 188 J/mol K
D) +537 J/mol K

Question 23

Calculate Δ S for the reaction:
SO₃( g ) + CaO( s ) → CaSO₄( s )
Δ S in J/mol K for: CaO( s ) = 40, SO₃( g ) = 256.6, CaSO₄( s ) = 107

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

Question 24

Calculate Δ G for the reaction:
2 NO₂( g ) → 2 N₂( g ) + O₂( g )
Δ G in kJ/mol for: NO₂( g ) = 51.30

A) +51.3
B) − 51.3
C) +103
D) − 103

Question 25

Calculate Δ G for the reaction:
SO₃( g ) + CaO( s ) → CaSO₄( s )
Δ G in kJ/mol for: CaO( s ) = − 604.2, SO₃( g ) = − 371.1, CaSO₄( s ) = − 1320

A) − 2230
B) − 345
C) − 323
D) +189

Question 26

The degradation of phosgene (COCl₂) into CO and Cl₂ happens to be non-spontaneous at room temperature and standard state conditions (273 K, 1 atm). What change in temperature must occur to make this a spontaneous reaction?

A) increase T
B) decrease T
C) add CO to the COCl₂
D) there is insufficient data to answer

Question 27

Calculate Δ G for the reaction:
2 SO₃( g ) → 2 SO₂( g ) + O₂( g )
Δ G in kJ/mol for: SO₂( g ) = − 300.2, SO₃( g ) = − 371.1

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

Question 28

Calculate Δ S for the reaction:
2 NO₂( g ) → 2 N₂( g ) + O₂( g )
Δ S in J/mol K for: NO₂( g ) = 240.0, N₂( g )= 191.5, O₂( g ) = 205.0

A) +157 J/K
B) − 157 J/K
C) +108 J/K
D) − 480 J/K

Question 29

When magnesium sulfite decomposes, the solid transforms into magnesium oxide and sulfur dioxide.
MgSO₃( s ) → MgO( s ) + SO₂( g )
At what temperature will this reaction be spontaneous according to Gibb's Energy?
Δ G in kJ/mol for: MgSO₃( s ) = − 1172, MgO( s ) = − 569.6, SO₂( g ) = − 300.2
Δ H in kJ/mol for: MgSO₃( s ) = − 1068, MgO( s ) = − 601.8, SO₂( g ) = − 296.8
Δ S in J/mol K for: MgSO₃( s ) = 121, MgO( s ) = 27, SO₂( g ) = 248.1

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

Question 30

Consider the 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 Gibb's Energy?
Δ H in kJ/mol for: CO( g ) = − 110.5, CO₂( g ) = − 393.5
Δ S in J/mol K for: CO( g ) = 197.6, CO₂( g ) = 213.6, O₂( g ) = 205.0

A) temps above − 63.1 K
B) temps below 179.5 K
C) temps above 415.8 K
D) temps below 3273 K