Thermodynamics: Laws, Enthalpy, Entropy, and Equilibrium

Question 1

Which of the following statements is NOT part of the first law of thermodynamics?

Accepted Answer

The entropy of an isolated system always increases.

Answer

Energy cannot be created or destroyed, only transferred or transformed.

Answer

The change in internal energy of a system is equal to the heat added to or removed from the system.

Answer

The total energy of an isolated system remains constant.

Question 2

Which of the following processes is spontaneous under standard conditions?

Accepted Answer

Sugar dissolving in water

Answer

Water freezing at room temperature

Answer

A ball rolling uphill

Answer

A chemical reaction that absorbs heat

Question 3

Enthalpy change (ΔH) is defined as:

Accepted Answer

The heat absorbed or released by a system at constant temperature and pressure.

Answer

The maximum work that can be done by a system at constant temperature and pressure.

Answer

The change in free energy of a system at constant temperature and pressure.

Answer

The change in entropy of a system at constant temperature and pressure.

Question 4

Which of the following factors does NOT affect the equilibrium constant (Kc) of a reaction?

Accepted Answer

Presence of a catalyst

Answer

Temperature

Answer

Pressure (for gas reactions only)

Answer

Concentration of reactants and products

Question 5

A negative standard Gibbs free energy change (ΔG°) indicates that:

Accepted Answer

The reaction is spontaneous at all temperatures.

Answer

The reaction is non-spontaneous at all temperatures.

Answer

The reaction is spontaneous at high temperatures only.

Answer

The spontaneity of the reaction depends on the temperature.

Question 6

Which equation represents the mathematical expression of the second law of thermodynamics?

Accepted Answer

ΔS ≥ 0

Answer

ΔH = 0

Answer

ΔG = 0

Answer

ΔU = ΔQ - ΔW

Question 7

Which of the following processes decreases the entropy of a system?

Accepted Answer

Compressing a gas

Answer

Dissolving a solid in water

Answer

Mixing two gases

Answer

Heating a gas

Question 8

An endothermic process is one in which:

Accepted Answer

Heat is absorbed

Answer

Heat is released

Answer

Entropy increases

Answer

Enthalpy decreases

Question 9

Which of the following reactions is exothermic?

Accepted Answer

Combustion of methane

Answer

Dissolution of ammonium chloride in water

Answer

Neutralization of hydrochloric acid with sodium hydroxide

Answer

Melting of ice

Question 10

Which of the following is NOT a factor that affects spontaneity?

Accepted Answer

Activation energy

Answer

Enthalpy change

Answer

Entropy change

Answer

Temperature

Question 11

What type of system is a sealed flask of air?

Accepted Answer

Closed system

Answer

Open system

Answer

Isolated system

Answer

Adiabatic system

Question 12

State the second law of thermodynamics.

Accepted Answer

The entropy of an isolated system never decreases.

Answer

The total energy of an isolated system remains constant.

Answer

The entropy of a system approaches a maximum with time.

Answer

The free energy of a system decreases with time.

Question 13

What is the symbol for the enthalpy change at constant pressure?

Accepted Answer

ΔH

Answer

ΔU

Answer

ΔS

Answer

ΔG

Question 14

Which of the following is an exothermic process?

Accepted Answer

Combustion of methane

Answer

Melting of ice

Answer

Freezing of water

Answer

Dissolution of salt in water

Question 15

Entropy measures the:

Accepted Answer

Disorderliness of a system

Answer

Orderliness of a system

Answer

Energy of a system

Answer

Volume of a system

Question 16

Gibbs free energy change (ΔG) represents the:

Accepted Answer

Maximum work available from a system

Answer

Minimum work needed to be done on a system

Answer

Heat transferred to the surroundings

Answer

Heat absorbed from the surroundings

Question 17

Hess's law is used to:

Accepted Answer

Calculate enthalpy change of a reaction using enthalpy changes of individual steps

Answer

Calculate entropy change of a reaction using entropy changes of individual steps

Answer

Calculate Gibbs free energy change of a reaction using Gibbs free energy changes of individual steps

Answer

Calculate equilibrium constant of a reaction using equilibrium constants of individual steps

Question 18

What is the direction of heat flow for a spontaneous process?

Accepted Answer

From hot to cold

Answer

From cold to hot

Answer

In both directions

Answer

No heat flow occurs

Question 19

Which of the following reactions has the largest positive enthalpy change?

Accepted Answer

Endothermic reaction

Answer

Exothermic reaction

Answer

Spontaneous reaction

Answer

Equilibrium reaction

Question 20

Under standard conditions, what is the relationship between the equilibrium constant (K) and the Gibbs free energy change (ΔG)?

Accepted Answer

ΔG = -RTlnK

Answer

ΔG = RTlnK

Answer

K = -ΔG/RT

Answer

K = ΔG/RT

Question 21

Which of the following factors does NOT affect the spontaneity of a chemical reaction?

Accepted Answer

Volume of the system

Answer

Enthalpy change

Answer

Entropy change

Answer

Temperature

Question 22

According to the third law of thermodynamics, what is the entropy of a pure crystalline substance at absolute zero?

Accepted Answer

Zero

Answer

Positive

Answer

Negative

Answer

Cannot be determined

Question 23

Which type of thermodynamic system can exchange both energy and matter with the surroundings?

Accepted Answer

Open system

Answer

Closed system

Answer

Isolated system

Answer

Microcanonical system

Question 24

Which principle states that the total energy of an isolated system remains constant?

Accepted Answer

First law of thermodynamics

Answer

Second law of thermodynamics

Answer

Third law of thermodynamics

Answer

Zeroth law of thermodynamics

Question 25

How is spontaneity related to Gibbs free energy?

Accepted Answer

Processes with negative Gibbs free energy changes are spontaneous.

Answer

Processes with positive Gibbs free energy changes are spontaneous.

Answer

Processes with zero Gibbs free energy changes are spontaneous.

Answer

Gibbs free energy changes are not related to spontaneity.

Question 26

Distinguish between endothermic and exothermic reactions.

Accepted Answer

Endothermic reactions absorb heat, while exothermic reactions release heat.

Answer

Exothermic reactions absorb heat, while endothermic reactions release heat.

Answer

Endothermic reactions decrease temperature, while exothermic reactions increase temperature.

Answer

Exothermic reactions decrease temperature, while endothermic reactions increase temperature.

Question 27

Describe how a change in temperature can influence the spontaneity of a reaction. Provide an example to illustrate your explanation.

Accepted Answer

Increasing temperature favors the forward reaction if it is endothermic, and the reverse reaction if it is exothermic.

Answer

Increasing temperature promotes spontaneity for exothermic reactions.

Answer

Decreasing temperature always enhances the spontaneity of reactions.

Question 28

What is the unit of entropy?

Accepted Answer

Joule per Kelvin

Answer

Joule

Answer

Kelvin

Answer

Celsius per mole

Question 29

Which of the following processes is exothermic?

Accepted Answer

Combustion of propane

Answer

Melting of ice

Answer

Freezing of water

Answer

Evaporation of ethanol

Question 30

Which of the following describes a system at equilibrium?

Accepted Answer

The forward and reverse reactions occur at the same rate, and the concentrations of the reactants and products do not change over time.

Answer

The forward and reverse reactions occur at different rates.

Answer

The concentrations of the reactants and products change over time.

Answer

The system is open to the exchange of matter.

Question 31

What is the definition of the standard free energy change for a reaction?

Accepted Answer

The change in free energy when the reactants and products are at their standard states.

Answer

The change in free energy when the reactants and products are at non-standard states.

Answer

The change in enthalpy when the reactants and products are at their standard states.

Answer

The change in entropy when the reactants and products are at their standard states.

Question 32

State the third law of thermodynamics and explain its significance in determining the entropy of a system at absolute zero.

Accepted Answer

As the temperature of a perfect crystal approaches absolute zero, its entropy approaches zero.

Answer

The entropy of a system increases as its temperature decreases.

Answer

The entropy of a system is a measure of its disorder.

Answer

The entropy of a pure substance remains constant at all temperatures.

Question 33

What is the sign of the enthalpy change for an exothermic reaction?

Accepted Answer

Negative

Answer

Positive

Answer

Zero

Answer

It depends on the temperature

Question 34

Which system is closed?

Accepted Answer

A sealed container of water

Answer

An open container of water

Answer

A room with an open window

Answer

A person breathing air

Question 35

Which of the following processes is considered exothermic?

Accepted Answer

Combustion of ethane

Answer

Melting of ice

Answer

Evaporation of water

Answer

Dissolving of sodium chloride in water

Question 36

Identify the process that is not spontaneous:

Accepted Answer

Oxidation of iron in moist air

Answer

Melting of ice at room temperature

Answer

Mixing of sugar and water

Answer

Evaporation of water in an open container

Question 37

Which formula accurately represents the entropy change of an isothermal process?

Accepted Answer

ΔS = Q/T

Answer

ΔS = ΔH/T

Answer

ΔS = -ΔG/T

Answer

ΔS = ΔE/T

Question 38

In a reaction with a positive enthalpy change, the reaction is:

Accepted Answer

Endothermic

Answer

Exothermic

Answer

Spontaneous

Answer

At equilibrium

Question 39

State the law of thermodynamics that describes the entropy of isolated systems:

Accepted Answer

Entropy always increases.

Answer

Energy cannot be created or destroyed.

Answer

All spontaneous reactions are irreversible.

Answer

The universe is continuously expanding.

Question 40

For an element in its standard state, the standard enthalpy of formation is:

Accepted Answer

0 kJ mol⁻¹

Answer

1 kJ mol⁻¹

Answer

10 kJ mol⁻¹

Answer

100 kJ mol⁻¹

Question 41

A reaction with a negative Gibbs free energy change is:

Accepted Answer

Spontaneous and exothermic

Answer

Spontaneous and endothermic

Answer

Non-spontaneous and exothermic

Answer

Non-spontaneous and endothermic

Question 42

Which of the following reactions has the smallest equilibrium constant (K)?

Accepted Answer

I + J ⇌ K + L (K = 0.1)

Answer

A + B ⇌ C + D (K = 1)

Answer

E + F ⇌ G + H (K = 10)

Answer

M + N ⇌ O + P (K = 100)

Question 43

Which of the following expressions correctly represents the Gibbs free energy (G)?

Accepted Answer

G = H - TS

Answer

G = TS - H

Answer

G = H + TS

Answer

G = H / TS