Chemical Reactions and Energy: Interactive Quizzes and Practice Questions

Question 1

Which of the following is **NOT** a property of a state function?

Accepted Answer

Can be used to determine the spontaneity of a reaction

Answer

Independent of the reaction pathway

Answer

Dependent on the initial and final state of the system

Answer

Has a definite value for a given state

Question 2

Which law states that the enthalpy change for a reaction is the same whether the reaction occurs in one step or multiple steps?

Accepted Answer

Hess's Law

Answer

First Law of Thermodynamics

Answer

Second Law of Thermodynamics

Answer

Gibbs' Law

Question 3

A reaction with a negative enthalpy change is:

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Adiabatic

Answer

Isothermal

Question 4

What is the SI unit of entropy?

Accepted Answer

Joules per kelvin (J/K)

Answer

Calories per degree Celsius (cal/°C)

Answer

Electronvolts per particle (eV/particle)

Answer

Watts per metre (W/m)

Question 5

What factor(s) determine the spontaneity of a reaction?

Accepted Answer

Enthalpy and entropy changes

Answer

Enthalpy change only

Answer

Entropy change only

Answer

Free energy change only

Question 6

The equilibrium constant for a reaction represents:

Accepted Answer

The extent to which the reaction proceeds

Answer

The rate of the forward reaction

Answer

The rate of the reverse reaction

Answer

The spontaneity of the reaction

Question 7

The activation energy of a reaction is:

Accepted Answer

The minimum energy required for a reaction to occur

Answer

The energy difference between the reactants and products

Answer

The energy released during a reaction

Answer

The energy absorbed during a reaction

Question 8

Which of the following is the correct definition of enthalpy change?

Accepted Answer

The change in energy of the system at constant pressure

Answer

The heat flow at constant temperature

Answer

The work done by the system

Answer

The change in energy of the system at constant volume

Question 9

Which of the following factors does NOT affect the entropy change of a reaction?

Accepted Answer

Enthalpy change of the reaction

Answer

Temperature

Answer

Number of moles of reactants and products

Answer

Physical state of the reactants and products

Question 10

Which of the following is an application of Hess's law?

Accepted Answer

Calculating the enthalpy change of a reaction that cannot be measured directly

Answer

Determining the equilibrium constant of a reaction

Answer

Predicting the products of a reaction

Answer

Measuring the rate of a reaction

Question 11

Which of the following is the correct definition of Gibbs free energy change?

Accepted Answer

The maximum amount of work that can be extracted from a reaction at constant temperature and pressure.

Answer

The change in enthalpy of the system at constant temperature and pressure.

Answer

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

Answer

The heat flow at constant temperature and pressure.

Question 12

According to Hess's law, how is the enthalpy change for a reaction defined?

Accepted Answer

The cumulative enthalpy changes of individual reaction steps

Answer

The difference between the enthalpy changes of reactants and products

Answer

Dependent on reaction temperature and pressure

Answer

Unpredictable from individual enthalpy changes

Question 13

Which of the following reactions is categorized as exothermic?

Accepted Answer

Combustion of methane

Answer

Neutralization of hydrochloric acid with sodium hydroxide

Answer

Dissolution of ammonium chloride in water

Answer

Evaporation of water

Question 14

What is the standard enthalpy change of formation for an element in its standard state?

Accepted Answer

0 kJ/mol

Answer

Always positive

Answer

Always negative

Answer

Varies with temperature and pressure

Question 15

What is the entropy change for an isothermal reversible process?

Accepted Answer

0

Answer

Always positive

Answer

Always negative

Answer

Cannot be determined

Question 16

Which reaction exhibits the greatest Gibbs free energy change?

Accepted Answer

Reaction with substantial negative enthalpy change and substantial positive entropy change

Answer

Reaction with substantial positive enthalpy change and minimal positive entropy change

Answer

Reaction with minimal negative enthalpy change and substantial positive entropy change

Answer

Reaction with minimal positive enthalpy change and minimal negative entropy change

Question 17

What is the function of a catalyst in a chemical reaction?

Accepted Answer

Decreases activation energy

Answer

Increases activation energy

Answer

Reactant that is consumed

Answer

Substance unaffected by the reaction

Question 18

The standard enthalpy change of formation for an element in its standard state is:

Accepted Answer

Zero

Answer

Positive

Answer

Negative

Answer

Cannot be determined

Question 19

In a spontaneous reaction, the relationship between enthalpy change (ΔH) and entropy change (ΔS) is:

Accepted Answer

ΔH is negative and ΔS is positive

Answer

ΔH is positive and ΔS is negative

Answer

ΔH and ΔS are both negative

Answer

ΔH and ΔS are both positive

Question 20

The graphical representation of the change in free energy (ΔG) of a reaction is called a:

Accepted Answer

Gibbs free energy diagram

Answer

Potential energy diagram

Answer

Energy level diagram

Answer

Enthalpy change diagram

Question 21

Which method is used to calculate the enthalpy change of a reaction indirectly?

Accepted Answer

Hess's law

Answer

Calorimetry

Answer

Stoichiometry

Answer

Spectroscopy

Question 22

For an exothermic reaction, the sign of the enthalpy change is:

Accepted Answer

Negative

Answer

Positive

Answer

Zero

Answer

Depends on the temperature

Question 23

The relationship between the Gibbs free energy change (ΔG) and the equilibrium constant (K) of a reaction is given by:

Accepted Answer

ΔG = -RTlnK

Answer

ΔG = RTlnK

Answer

ΔG = -K

Answer

ΔG = K

Question 24

An adiabatic reaction is characterized by:

Accepted Answer

No heat is transferred to or from the surroundings

Answer

The temperature of the system changes

Answer

The volume of the system changes

Answer

The pressure of the system changes

Question 25

The primary purpose of a reaction calorimeter is to:

Accepted Answer

Measure the enthalpy change of a reaction

Answer

Calculate the equilibrium constant of a reaction

Answer

Determine the rate of a reaction

Answer

Predict the products of a reaction

Question 26

What is the standard unit for expressing the enthalpy change of a chemical reaction?

Accepted Answer

Kilojoules per mole

Answer

Joules

Answer

Calories

Answer

Electronvolts

Question 27

According to Hess's law, the overall enthalpy change of a reaction is:

Accepted Answer

Equal to the sum of the enthalpy changes of the individual steps

Answer

Independent of the pathway

Answer

Dependent on the temperature

Answer

Positive for exothermic reactions

Question 28

Which of the following reactions is exothermic?

Accepted Answer

Combustion of methane

Answer

Dissolution of sodium chloride in water

Answer

Melting of ice

Answer

Evaporation of water

Question 29

Entropy is a measure of the:

Accepted Answer

Disorder or randomness of a system

Answer

Energy content of a system

Answer

Concentration of a solution

Answer

Temperature of a system

Question 30

A reaction with a negative Gibbs free energy change is:

Accepted Answer

Spontaneous

Answer

Non-spontaneous

Answer

Reversible

Answer

Irreversible

Question 31

Which of the following is NOT a standard state condition?

Accepted Answer

1 M concentration

Answer

298 K (25 °C)

Answer

1 atm pressure

Answer

Pure substance in its most stable form at 298 K

Question 32

Which of the following statements best describes the enthalpy change for an endothermic reaction?

Accepted Answer

A positive change in enthalpy, indicating the reaction absorbs heat from the surroundings.

Answer

A negative change in enthalpy, indicating the reaction releases heat to the surroundings.

Answer

No change in enthalpy, indicating the reaction neither absorbs nor releases heat.

Answer

The enthalpy change cannot be determined without additional information about the reaction.

Question 33

Which of the following factors does NOT influence the equilibrium constant of a reaction?

Accepted Answer

Presence of a catalyst

Answer

Temperature

Answer

Pressure (for gaseous reactions)

Answer

Concentration of reactants

Question 34

According to convention, what is the standard enthalpy change of formation for an element in its standard state?

Accepted Answer

0 kJ/mol

Answer

A positive value (greater than 0 kJ/mol)

Answer

A negative value (less than 0 kJ/mol)

Answer

Cannot be determined

Question 35

What determines the spontaneity of a reaction?

Accepted Answer

Both enthalpy and entropy changes

Answer

Enthalpy change alone

Answer

Entropy change alone

Answer

Neither enthalpy nor entropy changes

Question 36

Which of the following reactions typically has the largest negative enthalpy change?

Accepted Answer

Combustion of hydrocarbons (e.g., methane)

Answer

Neutralization of a strong acid and base

Answer

Dissolution of ionic compounds (e.g., sodium chloride) in water

Answer

Formation of water from hydrogen and oxygen

Question 37

What is the relationship between the enthalpy change for the forward reaction and the enthalpy change for the reverse reaction?

Accepted Answer

They have the same magnitude but opposite signs.

Answer

They have the same magnitude and the same sign.

Answer

The enthalpy change for the reverse reaction is half of the enthalpy change for the forward reaction.

Answer

The enthalpy change for the reverse reaction cannot be determined without additional information.

Question 38

At equilibrium, what is the value of the Gibbs free energy change (ΔG) for a reaction?

Accepted Answer

Exactly zero

Answer

Positive

Answer

Negative

Answer

Cannot be determined without additional information

Question 39

A chemical reaction has a positive ΔG value. What can you infer about the spontaneity of this reaction?

Accepted Answer

The reaction occurs spontaneously in the reverse direction.

Answer

The reaction occurs spontaneously in the forward direction.

Answer

The reaction is in equilibrium.

Question 40

Which of the following best describes enthalpy change?

Accepted Answer

The heat energy change at constant pressure during a chemical reaction.

Answer

The measure of disorder or randomness in a system.

Answer

The total energy of a system at constant volume.

Question 41

A reaction is considered exothermic when:

Accepted Answer

The enthalpy change of the reaction is negative, and heat is released to the surroundings.

Answer

The enthalpy change of the reaction is zero, and no heat exchange occurs.

Answer

The enthalpy change of the reaction is positive, and heat is absorbed from the surroundings.

Question 42

Which of the following increases the entropy of a system?

Accepted Answer

Sublimation of solid carbon dioxide (dry ice)

Answer

Crystallization of salt from a solution

Answer

Condensation of steam

Answer

Freezing water into ice

Question 43

Gibbs free energy (G) combines enthalpy and entropy to determine:

Accepted Answer

The spontaneity of a reaction at a given temperature.

Answer

The activation energy of a reaction.

Answer

The rate of a chemical reaction.

Question 44

The standard enthalpy change of combustion refers to the enthalpy change when:

Accepted Answer

One mole of a substance is completely burned in excess oxygen under standard conditions.

Answer

One mole of a substance reacts with a limited amount of oxygen.

Answer

One gram of a substance is burned in air at room temperature.

Question 45

The units for entropy change are:

Accepted Answer

J K⁻¹ mol⁻¹

Answer

kJ K⁻¹

Answer

kJ mol⁻¹

Answer

J mol⁻¹

Question 46

Which of the following statements correctly describes the enthalpy change for an endothermic reaction?

Accepted Answer

The enthalpy change is positive, meaning energy is absorbed from the surroundings.

Answer

The enthalpy change is negative, meaning energy is released to the surroundings.

Answer

The enthalpy change is always zero.

Question 47

A reaction has a negative enthalpy change and a positive entropy change. Which of the following statements is true about this reaction?

Accepted Answer

The reaction is spontaneous at all temperatures.

Answer

The reaction is spontaneous at low temperatures but non-spontaneous at high temperatures.

Answer

The reaction is non-spontaneous at all temperatures.

Answer

The reaction is spontaneous at high temperatures but non-spontaneous at low temperatures.

Question 48

The standard enthalpy change of formation of carbon dioxide is -393.5 kJ/mol. What is the enthalpy change for the combustion of 1 mole of carbon?

Accepted Answer

-393.5 kJ

Answer

+196.8 kJ

Answer

-196.8 kJ

Answer

+393.5 kJ

Question 49

Which of the following processes is exothermic?

Accepted Answer

The condensation of water vapor.

Answer

The melting of ice.

Answer

The dissolution of ammonium nitrate in water.

Answer

The sublimation of iodine.

Question 50

The standard enthalpy change of combustion of methane is -890 kJ/mol. What is the enthalpy change when 2 moles of methane are completely combusted?

Accepted Answer

-1780 kJ

Answer

-890 kJ

Answer

+890 kJ

Answer

+1780 kJ

Question 51

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

Accepted Answer

The color of the reactants.

Answer

The entropy change.

Answer

The enthalpy change.

Answer

The temperature.

Question 52

The standard enthalpy change of formation of water is -285.8 kJ/mol. What is the enthalpy change for the following reaction? 
 2H₂(g) + O₂(g) → 2H₂O(l)

Accepted Answer

-571.6 kJ

Answer

+285.8 kJ

Answer

-285.8 kJ

Answer

+571.6 kJ

Question 53

A reaction has a positive enthalpy change and a positive entropy change. Under what conditions will this reaction be spontaneous?

Accepted Answer

At high temperatures.

Answer

At low temperatures.

Answer

At all temperatures.

Question 54

Which of the following is the correct definition of entropy?

Accepted Answer

A measure of the disorder or randomness of a system.

Answer

A measure of the rate of a reaction.

Answer

A measure of the energy content of a system.

Question 55

Consider the following reaction: 
 N₂(g) + 3H₂(g) → 2NH₃(g) 
 What is the enthalpy change for the reaction if the enthalpy changes of formation of NH₃(g), N₂(g), and H₂(g) are -46.1 kJ/mol, 0 kJ/mol, and 0 kJ/mol, respectively?

Accepted Answer

-92.2 kJ

Answer

+46.1 kJ

Answer

-46.1 kJ

Answer

+92.2 kJ