Thermodynamics Quizzes: Test Your Understanding

Question 1

In a closed system at equilibrium, what happens to its entropy?

Accepted Answer

Remains constant over time

Answer

Decreases over time

Answer

Increases over time

Answer

Changes unpredictably

Question 2

In a spontaneous process, what happens to the entropy of the system?

Accepted Answer

Entropy increases.

Answer

Entropy remains constant.

Answer

Entropy decreases.

Answer

Entropy change is unpredictable.

Question 3

During an isothermal reversible expansion, what occurs to the system's entropy?

Accepted Answer

Increases

Answer

Decreases

Answer

Stays the same

Answer

Drops to zero

Question 4

What is the most accurate definition of entropy in a system?

Accepted Answer

Entropy measures the level of randomness or disorder in a system.

Answer

Entropy is a quantity that remains constant in all processes.

Answer

Entropy can have negative values in some systems.

Answer

Entropy is a measure of the heat energy in a system.

Question 5

At equilibrium, what does the Gibbs free energy change (ΔG°) of a reaction represent?

Accepted Answer

The maximum useful work obtainable from the reaction.

Answer

The reaction's spontaneity is independent of temperature.

Answer

The reaction's enthalpy change is always negative.

Answer

The system's entropy always decreases.

Question 6

Which of the following processes is spontaneous, according to the Second Law of Thermodynamics?

Accepted Answer

Mixing two gases at different temperatures

Accepted Answer

A chemical reaction that releases heat

Accepted Answer

A solid dissolving in a liquid

Answer

Heat flowing from a cold object to a hot object

Question 7

According to the second law of thermodynamics, what is the fate of the total entropy of an isolated system over time?

Accepted Answer

Increases

Answer

Decreases

Answer

Stays the same

Answer

Varies unpredictably

Question 8

Which statement does NOT describe the second law of thermodynamics?

Accepted Answer

Heat flows spontaneously from a cold reservoir to a hot reservoir.

Answer

The entropy of an isolated system increases over time.

Answer

No heat engine can be perfectly efficient.

Answer

The total entropy of the universe is always increasing.

Question 9

In an isolated system undergoing an irreversible process, what happens to the entropy of the system according to the second law of thermodynamics?

Accepted Answer

The entropy increases.

Answer

The entropy remains constant.

Question 10

According to the second law of thermodynamics, which statement describes the direction of spontaneous processes?

Accepted Answer

Spontaneous processes increase the total entropy of the system and its surroundings.

Answer

Spontaneous processes decrease the total entropy of the system and its surroundings.

Answer

Spontaneous processes decrease the free energy of the system.

Answer

Spontaneous processes increase the enthalpy of the system.

Question 11

According to the second law of thermodynamics, what happens to the entropy of an isolated system over time?

Accepted Answer

Increases, leading to a more disordered state

Answer

Decreases, leading to a more ordered state

Answer

Remains constant, as the system reaches equilibrium

Answer

Fluctuates randomly, with no discernible pattern

Question 12

In a closed system undergoing a reversible isothermal process, what happens to the system's entropy?

Accepted Answer

Remains constant

Answer

Increases

Answer

Decreases

Answer

Becomes zero

Question 13

In an isothermal expansion of a van der Waals gas, what happens to the entropy change (ΔS)?

Accepted Answer

ΔS is positive because the gas becomes more disordered as it expands.

Answer

ΔS is negative because the gas expands, doing work on its surroundings.

Answer

ΔS is zero because the temperature remains constant.

Question 14

Enthalpy is defined as the change in a system's:

Accepted Answer

Heat content at constant pressure

Answer

Internal energy at constant volume

Answer

Entropy at constant temperature

Answer

Gibbs free energy at constant volume

Question 15

The Gibbs free energy of a system is a measure of its:

Accepted Answer

Maximum non-expansion work

Answer

Minimum work required

Answer

Total energy

Answer

Entropy

Question 16

Which of the following is an example of an open system in thermodynamics?

Accepted Answer

A beaker of evaporating water

Answer

A sealed flask of gas

Answer

A closed container of liquid

Answer

An isolated system

Question 17

Which thermodynamic potential is most useful for determining the spontaneity of a reaction?

Accepted Answer

Gibbs free energy

Answer

Internal energy

Answer

Enthalpy

Answer

Helmholtz free energy

Question 18

Which of the following is the correct mathematical expression for the first law of thermodynamics?

Accepted Answer

dU = dQ - dW

Answer

dQ = dU + dW

Answer

dW = dQ - dU

Answer

dU = dW + dQ

Question 19

What is the SI unit of entropy?

Accepted Answer

Joule per Kelvin (J/K)

Answer

Calorie per Kelvin (cal/K)

Answer

Kilojoule per gram-mole Kelvin (kJ/g-mol K)

Answer

Watt per Kelvin (W/K)

Question 20

For an ideal gas, what is the relationship between enthalpy (H) and internal energy (U)?

Accepted Answer

H = U + PV

Answer

H = U - PV

Answer

U = H + PV

Answer

U = H - PV

Question 21

Identify the thermodynamic process that occurs at constant pressure:

Accepted Answer

Evaporation of water at a constant temperature

Answer

Expansion of a gas into a vacuum

Answer

Adiabatic compression of a gas

Answer

Melting of ice at a constant volume

Question 22

In a combustion engine, exergy represents:

Accepted Answer

The maximum useful work obtainable by bringing the system to equilibrium with its surroundings, considering entropy generation.

Answer

The total energy content of the system, including kinetic and potential energy.

Answer

The minimum work needed to bring the system to a specific state.

Answer

A measure of the system's randomness or disorder.

Question 23

State the First Law of Thermodynamics.

Accepted Answer

Energy can neither be created nor destroyed, but can only be transferred or transformed.

Answer

Entropy always increases in an isolated system.

Answer

Heat flows from higher to lower temperatures.

Answer

The change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

Question 24

What is the SI unit of entropy?

Accepted Answer

Joule per Kelvin

Answer

Kelvin

Answer

Joule

Answer

Pascal

Question 25

Which technique determines the spontaneity of a reaction?

Accepted Answer

Gibbs free energy change

Answer

Enthalpy change

Answer

Entropy change

Answer

Reaction rate

Question 26

Under non-standard conditions, how can you determine if a chemical reaction is spontaneous using enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG)?

Accepted Answer

Calculate ΔG at non-standard conditions using ΔH and ΔS.

Answer

Check the sign of ΔH to determine spontaneity.

Answer

Check the sign of ΔS to determine spontaneity.

Question 27

Which statement accurately describes the first law of thermodynamics?

Accepted Answer

Energy can be converted from one form to another.

Answer

Energy can be created or destroyed.

Answer

The entropy of an isolated system always increases.

Answer

The free energy of a system is always positive.

Question 28

Which of the following units is used to measure enthalpy?

Accepted Answer

Joules (J)

Answer

Newtons (N)

Answer

Pascals (Pa)

Answer

Kelvin (K)

Question 29

Which process releases heat to the surroundings?

Accepted Answer

Combustion of gasoline

Answer

Melting of ice

Answer

Evaporation of water

Answer

Condensation of steam

Question 30

Which statement describes the relationship between entropy and disorder?

Accepted Answer

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

Answer

Disorder is a measure of the entropy of a system.

Answer

Entropy and disorder are unrelated concepts.

Answer

Entropy is inversely proportional to disorder.

Question 31

Which factor does NOT affect the free energy of a system?

Accepted Answer

Mass

Answer

Temperature

Answer

Pressure

Answer

Volume

Question 32

Which equation represents the Gibbs free energy?

Accepted Answer

G = H - TS

Answer

G = U + PV

Answer

G = S - PV

Answer

G = H + PV

Question 33

Which system is closed, allowing neither mass nor energy to enter or leave?

Accepted Answer

A sealed container of gas

Answer

A room with an open window

Answer

A pot of boiling water

Answer

A car engine

Question 34

What is the maximum theoretical efficiency of a Carnot engine?

Accepted Answer

It depends on the temperature of the heat reservoirs.

Answer

100%

Answer

50%

Answer

25%

Question 35

Which process is considered non-spontaneous?

Accepted Answer

Melting of ice at room temperature

Answer

Diffusion of gases

Answer

Combustion of propane

Answer

Evaporation of water at 100°C

Question 36

When a system expands against an external pressure, what is the sign of the work done?

Accepted Answer

Positive

Answer

Negative

Answer

Zero

Answer

It depends on the volume change.

Question 37

According to the second law of thermodynamics, spontaneous processes tend to occur in which direction?

Accepted Answer

From ordered to disordered states

Answer

From low energy to high energy states

Answer

From equilibrium to non-equilibrium states

Answer

From non-spontaneous to spontaneous states

Question 38

The enthalpy of a system is defined as:

Accepted Answer

Internal energy + pressure volume

Answer

Internal energy - pressure volume

Answer

Entropy + temperature

Answer

Gibbs free energy - temperature

Question 39

Which of the following processes is isentropic?

Accepted Answer

Reversible adiabatic compression

Answer

Irreversible isothermal expansion

Answer

Adiabatic combustion

Answer

Isothermal heat transfer

Question 40

The Gibbs free energy of a system is:

Accepted Answer

The maximum amount of non-expansion work that can be done by the system

Answer

The minimum amount of work that must be done on the system

Answer

The change in entropy of the system

Answer

The change in enthalpy of the system

Question 41

A reversible process is one in which:

Accepted Answer

The system returns to its initial state after the process

Answer

The entropy of the system decreases

Answer

The temperature of the system remains constant

Answer

The work done by the system is zero

Question 42

The heat transfer coefficient is a measure of:

Accepted Answer

The rate at which heat is transferred per unit area and temperature difference

Answer

The temperature difference between the fluid and the surface

Answer

The thermal conductivity of the fluid

Answer

The specific heat capacity of the fluid

Question 43

How does the number of microstates in a system relate to its entropy?

Accepted Answer

The number of microstates is directly proportional to entropy.

Answer

The number of microstates is inversely proportional to entropy.

Answer

There is no relationship between the number of microstates and entropy.

Question 44

According to the Second Law of Thermodynamics, why are heat engines and refrigeration cycles limited in their efficiency?

Accepted Answer

Heat engines cannot be 100% efficient because heat is lost to the environment.

Accepted Answer

Refrigeration cycles cannot be 100% efficient because heat is lost to the environment.

Answer

Heat can spontaneously flow from a colder to a hotter body.

Answer

The entropy of an isolated system can only decrease.

Question 45

How does heat transfer contribute to entropy generation in irreversible processes, particularly when there are temperature differences?

Accepted Answer

Heat transfer between systems at different temperatures increases entropy.

Answer

Entropy generation in irreversible processes is unrelated to heat transfer.

Answer

Heat transfer only occurs in reversible processes and does not contribute to entropy generation.

Answer

Heat transfer always decreases entropy, making the process irreversible.

Question 46

What is exergy, and how does it help us understand the efficiency and sustainability of energy conversion processes?

Accepted Answer

Exergy is the maximum useful work obtainable from a system during a reversible process, considering its state and the environment.

Answer

Exergy is identical to enthalpy, both measuring a system's total energy.

Answer

Exergy is an outdated concept with limited practical use in modern thermodynamics.

Answer

Exergy applies only to closed systems, not open systems with mass flow.

Question 47

How does exergy analysis contribute to optimizing engineering system performance?

Accepted Answer

It pinpoints areas for improvement by quantifying the potential for optimization.

Answer

It's mainly used to evaluate heat engines and power plants.

Answer

It's only applicable to advanced research projects.

Answer

It's only relevant for systems operating at high temperatures.

Question 48

Under non-standard conditions, the spontaneity of a reaction is determined by:

Accepted Answer

Both the sign of ΔG and the temperature and pressure of the system.

Answer

The sign of the Gibbs free energy change (ΔG).

Answer

The temperature and pressure of the system.

Answer

The enthalpy change (ΔH) of the reaction.

Question 49

Explain how thermodynamics and materials science are interconnected, providing a specific example to illustrate their interdisciplinary nature.

Accepted Answer

Thermodynamics helps predict phase transitions in materials, guiding the design of materials with specific properties.

Answer

Thermodynamics is unrelated to materials science, as it only deals with energy and heat.

Answer

Thermodynamics can calculate energy transfer efficiency in materials but has no role in materials design.

Answer

Thermodynamics applies only to chemical reactions, not to material properties.

Question 50

Enthalpy (H) is defined as:

Accepted Answer

H = U + P V

Answer

H = U - P V

Answer

H = T S

Answer

H = G + T S

Question 51

A system undergoes a process in which its internal energy decreases while heat is added to the system. Which of the following statements is true?

Accepted Answer

Work is done on the system

Answer

Work is done by the system

Answer

The process is adiabatic

Answer

The process is isobaric

Question 52

Which of the following is the SI unit of entropy?

Accepted Answer

Joule per Kelvin

Answer

Joule

Answer

Kelvin

Answer

Kelvin per Joule

Question 53

A heat engine operating between two reservoirs at temperatures T1 and T2 (T1 > T2) has a maximum possible efficiency of:

Accepted Answer

(T1 - T2) / T2

Answer

T1 / T2

Answer

T2 / T1

Answer

(T1 - T2) / T1

Question 54

A refrigerator operates by:

Accepted Answer

Removing heat from a hot reservoir and transferring it to a cold reservoir

Answer

Removing heat from a cold reservoir and transferring it to a hot reservoir

Answer

Adding heat to a cold reservoir and transferring it to a hot reservoir

Answer

Adding heat to a hot reservoir and transferring it to a cold reservoir

Question 55

According to the First Law of Thermodynamics, what happens to energy in a closed system?

Accepted Answer

Energy cannot be created or destroyed, only transferred or transformed

Answer

Energy is always lost to the surroundings

Answer

Energy is always converted into heat

Answer

Energy can be created from nothing

Question 56

Which of the following is a quantitative measure of the disorder of a system?

Accepted Answer

Entropy

Answer

Internal energy

Answer

Gibbs free energy

Answer

Enthalpy

Question 57

Which of the following is a characteristic of a closed system?

Accepted Answer

No mass can enter or leave the system

Answer

The temperature of the system is constant

Answer

The pressure of the system is constant

Answer

The volume of the system is constant

Question 58

Which thermodynamic potential is most commonly used to predict the spontaneity of a reaction at constant temperature and pressure?

Accepted Answer

Gibbs free energy

Answer

Enthalpy

Answer

Internal energy

Answer

Entropy

Question 59

Which of the following processes can be reversed by an infinitesimal change in conditions?

Accepted Answer

A reversible process

Answer

A spontaneous process

Answer

An irreversible process

Answer

An adiabatic process

Question 60

During an adiabatic process, what happens to the system's heat transfer?

Accepted Answer

No heat is transferred into or out of the system

Answer

Heat is transferred reversibly

Answer

Heat is transferred into the system

Answer

Heat is transferred out of the system

Question 61

Which of the following is a collection of matter that is being studied in thermodynamics?

Accepted Answer

A thermodynamic system

Answer

The universe

Answer

The surroundings

Answer

A process

Question 62

A substance with a definite composition and a unique set of properties is known as:

Accepted Answer

A pure substance

Answer

A solution

Answer

A compound

Answer

A mixture

Question 63

Which of the following is a form of energy transfer that occurs due to a temperature difference?

Accepted Answer

Heat

Answer

Work

Answer

Sound

Answer

Light

Question 64

Which of the following correctly encapsulates the essence of the first law of thermodynamics?

Accepted Answer

Energy cannot be created nor destroyed, only transferred or changed in form.

Answer

Entropy always increases within a closed system.

Answer

Heat is a form of energy that can be transferred between systems.