Thermodynamics: Master the Laws of Energy and Matter

Question 1

Under which condition is the change in free energy for a reaction equal to zero?

Accepted Answer

When the reaction is at equilibrium.

Answer

When the reaction is exothermic.

Answer

When the reaction is endothermic.

Answer

When the enthalpy change of the reaction is zero.

Question 2

How is the Gibbs free energy related to the equilibrium constant?

Accepted Answer

The equilibrium constant is equal to the exponential of the negative Gibbs free energy divided by the gas constant multiplied by temperature.

Answer

The Gibbs free energy is equal to the exponential of the negative equilibrium constant divided by the gas constant multiplied by temperature.

Answer

The equilibrium constant is inversely proportional to the Gibbs free energy.

Answer

The Gibbs free energy is inversely proportional to the equilibrium constant.

Question 3

What is the entropy change of a system undergoing a phase transition from solid to liquid?

Accepted Answer

Positive

Answer

Negative

Answer

Zero

Answer

Dependent on the substance.

Question 4

Which of the following processes is reversible?

Accepted Answer

The expansion of a gas into a vacuum.

Answer

The combustion of a fuel.

Answer

The freezing of water.

Answer

The dissolution of salt in water.

Question 5

How is the efficiency of a heat engine defined?

Accepted Answer

The ratio of the work output to the heat input.

Answer

The ratio of the heat input to the work output.

Answer

The difference between the work output and the heat input.

Answer

The sum of the work output and the heat input.

Question 6

Which property is NOT characteristic of a state function?

Accepted Answer

Dependence on system history

Answer

Path independence

Answer

Uniqueness for a given state

Answer

Definable for both closed and open systems

Question 7

In an isothermal process, which quantity remains constant?

Accepted Answer

Temperature

Answer

Pressure

Answer

Volume

Answer

Enthalpy

Question 8

Which equation represents the change in free energy (ΔG)?

Accepted Answer

ΔG = ΔH - TΔS

Answer

ΔG = ΔS - TΔH

Answer

ΔG = ΔH + TΔS

Answer

ΔG = TΔS - ΔH

Question 9

For a reversible process, which statement is true?

Accepted Answer

The system returns to its initial state after the process.

Answer

The system exchanges heat with the surroundings.

Answer

The entropy of the universe decreases.

Answer

The free energy of the system increases.

Question 10

What is the SI unit of entropy?

Accepted Answer

Joule per Kelvin

Answer

Joule

Answer

Kelvin

Answer

Calorie

Question 11

Which process is classified as exothermic?

Accepted Answer

Burning of gasoline

Answer

Melting of ice

Answer

Condensation of water

Answer

Sublimation of dry ice

Question 12

What does entropy measure in a thermodynamic system?

Accepted Answer

Disorder or randomness

Answer

Energy content

Answer

Temperature

Answer

Volume

Question 13

In the Carnot cycle, why are isothermal processes crucial for maximizing efficiency?

Accepted Answer

They facilitate reversible heat transfer with the surroundings, minimizing entropy generation and maximizing efficiency.

Answer

They increase the temperature difference between the heat reservoirs, leading to higher efficiency.

Answer

They allow for adiabatic expansion and compression, reducing heat loss and increasing efficiency.

Answer

They maintain a constant volume, preventing the system from doing work and reducing efficiency.

Question 14

In a reaction between hydrogen and oxygen to form water, the standard enthalpy of formation of water is -286 kJ/mol. What does this value indicate?

Accepted Answer

The energy released when one mole of water is formed from hydrogen and oxygen gases.

Answer

The energy required to break the O-H bonds in water molecules.

Answer

The energy required to convert one mole of water to hydrogen and oxygen gases.

Question 15

How can scientists use entropy changes to predict if a reaction will occur spontaneously?

Accepted Answer

An increase in entropy indicates a spontaneous reaction.

Answer

A decrease in entropy indicates a spontaneous reaction.

Answer

An increase in entropy indicates a non-spontaneous reaction.

Answer

Entropy change is not related to reaction spontaneity.

Question 16

How does free energy determine whether a cellular reaction will occur spontaneously?

Accepted Answer

Reactions are spontaneous when free energy decreases.

Answer

Free energy only applies to reactions involving gases.

Answer

Free energy is unrelated to enthalpy and entropy changes.

Answer

Reactions with positive free energy changes are always spontaneous.

Question 17

Which of the following is NOT a characteristic of a thermodynamic system?

Accepted Answer

Has neither mass nor volume

Answer

Exchanges heat but not mass with its surroundings

Answer

Exchanges neither mass nor energy with its surroundings

Answer

Allows for exchange of both mass and energy with its surroundings

Question 18

According to the first law of thermodynamics, energy:

Accepted Answer

cannot be created or destroyed, only transferred or transformed.

Answer

can be created or destroyed in open systems.

Answer

is always conserved in closed systems.

Question 19

Which of the following is the unit of entropy?

Accepted Answer

Joules per Kelvin (J/K)

Answer

Degrees Celsius per Kelvin (°C/K)

Answer

Calories per gram (cal/g)

Answer

Joules per mole (J/mol)

Question 20

Which of the following processes is spontaneous?

Accepted Answer

The diffusion of a gas from a high-concentration region to a low-concentration region.

Answer

The compression of a gas without the release of heat.

Answer

The freezing of water at 25°C.

Answer

The combustion of wood in the absence of oxygen.

Question 21

The Gibbs free energy of a system is equal to:

Accepted Answer

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

Answer

The total energy of the system.

Answer

The change in entropy of the surroundings.

Question 22

Which of the following is a closed system?

Accepted Answer

A sealed container of gas.

Answer

A room with an open door.

Answer

A pot of boiling water.

Answer

A car engine running at a constant speed.

Question 23

The heat capacity of a substance is defined as:

Accepted Answer

The amount of heat required to raise the temperature of 1 gram of the substance by 1 Kelvin.

Answer

The amount of heat required to melt the substance.

Answer

The amount of heat required to vaporize the substance.

Question 24

In an adiabatic process, the change in internal energy of the system is:

Accepted Answer

Zero.

Answer

Positive.

Answer

Equal to the heat transferred to the system.

Answer

Equal to the work done by the system.

Question 25

The second law of thermodynamics states that:

Accepted Answer

The entropy of an isolated system always increases over time.

Answer

Energy cannot be created or destroyed.

Answer

Heat always flows from hot to cold objects.