Question 1

Which process is the best example of a spontaneous process?

Accepted Answer

The reaction of hydrogen and oxygen to form water is a spontaneous process because it occurs naturally without the need for external energy to drive it. This process releases energy, making it energetically favorable and thus spontaneous.

Question 2

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

Accepted Answer

Entropy generally increases with temperature. At 135 °C, water is in a gaseous state (steam), which has higher entropy than liquid or solid states.

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.

Accepted Answer

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

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?

Accepted Answer

Entropy decreases when a gas is cooled because the molecules have less kinetic energy and their movement becomes more ordered.

Question 5

All exothermic processes are spontaneous

Accepted Answer

Not all exothermic processes are spontaneous. Spontaneity depends on both enthalpy change and entropy change according to the Gibbs free energy equation, ΔG = ΔH - TΔS. A process can be exothermic (ΔH < 0) but still non-spontaneous if the entropy decreases sufficiently (ΔS < 0) and the temperature is high enough.

Question 6

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

Accepted Answer

Exothermic reactions with negative values of $ \Delta S^\circ $ (change in entropy) are not necessarily spontaneous at all temperatures. The spontaneity of a reaction depends on the Gibbs free energy change ($ \Delta G^\circ $), which is influenced by both $ \Delta H^\circ $ (enthalpy change) and $ \Delta S^\circ $ (entropy change), as well as the temperature of the system. For a reaction with $ \Delta H^\circ < 0 $ (exothermic) and $ \Delta S^\circ < 0 $ (decrease in entropy), $ \Delta G^\circ $ becomes less negative or even positive as the temperature increases, making the reaction non-spontaneous at high temperatures.

Question 7

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

Accepted Answer

Recycled PET often requires extensive cleaning and processing to meet the standards for food-grade packaging, which can make it more expensive than using virgin PET. Additionally, the collection, sorting, and recycling processes add extra costs.

Question 8

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

Accepted Answer

The combustion of glucose is an exothermic reaction, releasing energy. Exothermic reactions are generally spontaneous because they lead to an increase in the entropy of the universe, making them favorable at all temperatures.

Question 9

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

Accepted Answer

Spontaneous processes at lower temperatures are often enthalpy driven because the enthalpy change (ΔH) is negative and dominates the Gibbs free energy equation (ΔG = ΔH - TΔS) when the temperature is low.

Question 10

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

Accepted Answer

Entropy increases as a system moves toward more random distributions of particles, reflecting a higher degree of disorder.

Question 11

Entropy is a state function.

Accepted Answer

Entropy is a state function because its value depends only on the current state of the system, not on the path taken to reach that state.

Question 12

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

Accepted Answer

The reaction involves a gas reactant forming a solid product, which decreases the disorder of the system, leading to a negative ΔS.

Question 13

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

Accepted Answer

During the recycling process, the polymer chains of PET (polyethylene terephthalate) can undergo thermal and mechanical stress, leading to chain scission and thus shorter average chain lengths.

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?

Accepted Answer

Opening the valve allows the nitrogen gas to spread out from the left flask into both flasks, increasing the disorder of the system, which results in an increase in entropy.

Question 15

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

Accepted Answer

The spontaneity of a reaction depends on both ΔS° (entropy change) and ΔH° (enthalpy change) as well as the temperature, according to the Gibbs free energy equation ΔG° = ΔH° - TΔS°. A positive ΔS° alone does not guarantee spontaneity without considering ΔH° and T.

Question 16

The randomness of a system may be described as its:

Accepted Answer

Entropy is a measure of the randomness or disorder within a system.

Question 17

Which statement best describes the change in entropy during the synthesis of a polymer?

Accepted Answer

The synthesis of a polymer involves combining many small molecules (monomers) into a single, larger molecule. This process results in a decrease in entropy because the system goes from a state of higher disorder (many individual molecules) to a state of lower disorder (fewer, larger molecules).

Question 18

According to the Second Law of Thermodynamics, the entropy of the universe must ____ for a spontaneous process?

Accepted Answer

The Second Law of Thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. For a spontaneous process, the entropy of the universe must increase.

Question 19

The entropy of a system approaches zero as:

Accepted Answer

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is exactly equal to zero. As a system approaches absolute zero, its entropy approaches zero because the particles in the system become perfectly ordered.

Question 20

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

Accepted Answer

Spontaneity of a process indicates the thermodynamic favorability of the reaction or process occurring without external intervention, but it does not provide information about the rate or speed at which the process will occur.

Quiz 10: Entropy and the Second Law of Thermodynamics

Which process is the best example of a spontaneous process?

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

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

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?

All exothermic processes are spontaneous

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

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

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

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

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

Entropy is a state function.

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

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

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?

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

The randomness of a system may be described as its:

Which statement best describes the change in entropy during the synthesis of a polymer?

According to the Second Law of Thermodynamics, the entropy of the universe must ____ for a spontaneous process?

The entropy of a system approaches zero as:

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

Quiz 10: Entropy and the Second Law of Thermodynamics

Which process is the best example of a spontaneous process?

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

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

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?

All exothermic processes are spontaneous

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

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

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

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

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

Entropy is a state function.

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

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

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?

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

The randomness of a system may be described as its:

Which statement best describes the change in entropy during the synthesis of a polymer?

According to the Second Law of Thermodynamics, the entropy of the universe must ____ for a spontaneous process?

The entropy of a system approaches zero as:

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

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

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