Energetics of Reactions: Interactive Quizzes and Practice Questions

Question 1

Define the term enthalpy.

Accepted Answer

The heat transferred in or out of a system at constant pressure

Answer

The total energy of a system

Answer

The change in Gibbs free energy of a system

Answer

The entropy of a system

Question 2

Identify the exothermic reaction:

Accepted Answer

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

Answer

N2(g) + 3H2(g) → 2NH3(g)

Answer

2H2O(l) → 2H2(g) + O2(g)

Answer

CaCO3(s) → CaO(s) + CO2(g)

Question 3

Which reaction is spontaneous under standard conditions?

Accepted Answer

A reaction with a negative ΔG°

Answer

A reaction with a positive ΔG°

Answer

A reaction with a ΔG° of zero

Answer

A reaction with a ΔH° of zero

Question 4

Identify the process that involves a decrease in entropy:

Accepted Answer

Condensation of water vapor

Answer

Melting of ice

Answer

Dissolution of salt in water

Answer

Sublimation of dry ice

Question 5

Which reaction is predicted to have the largest equilibrium constant?

Accepted Answer

A reaction with a negative ΔG°

Answer

A reaction with a positive ΔG°

Answer

A reaction with a ΔG° of zero

Answer

A reaction with a large positive ΔH°

Question 6

Which of the following is the standard enthalpy change of formation of water?

Accepted Answer

-286 kJ mol-1 (heat released)

Answer

0 kJ mol-1 (no heat change)

Answer

+286 kJ mol-1 (heat absorbed)

Answer

+84 kJ mol-1

Question 7

During a reaction, the entropy of the system decreases. What does this indicate?

Accepted Answer

The reaction is endothermic and non-spontaneous.

Answer

The reaction is exothermic and spontaneous.

Answer

The reaction is spontaneous but the direction of heat flow is uncertain.

Answer

The reaction is non-spontaneous but the direction of heat flow is uncertain.

Question 8

The enthalpy change for the combustion of methane is -890 kJ mol-1. What is the enthalpy change when 10 g of methane is burnt?

Accepted Answer

-178 kJ

Answer

-89 kJ

Answer

-890 kJ

Answer

-1780 kJ

Question 9

Which of the following reactions has the most negative entropy change?

Accepted Answer

Sublimation of dry ice

Answer

Melting of ice

Answer

Dissolution of salt in water

Answer

Combustion of methane

Question 10

An endothermic reaction is carried out at constant pressure. What will happen to the volume of the system?

Accepted Answer

Increase

Answer

Decrease

Answer

Remain the same

Answer

Cannot be determined from the information given

Question 11

Define enthalpy change.

Accepted Answer

The heat absorbed or released at constant pressure

Answer

The change in internal energy of a system at constant volume

Answer

The maximum amount of work a system can do

Answer

The spontaneous tendency of a system to decrease in entropy

Question 12

Which of the following does NOT affect the equilibrium constant of a reaction?

Accepted Answer

Presence of a catalyst

Answer

Temperature

Answer

Pressure

Answer

Concentration of reactants and products

Question 13

A reaction with a positive Gibbs free energy change is:

Accepted Answer

Non-spontaneous

Answer

Spontaneous

Answer

Exothermic

Answer

Endothermic

Question 14

Which of the following is NOT a unit of energy?

Accepted Answer

Entropy

Answer

Joule

Answer

Calorie

Answer

Kilojoule per mole

Question 15

Define the bond enthalpy of a bond.

Accepted Answer

Energy required to break the bond

Answer

Energy released when the bond is formed

Answer

Average energy of all the bonds in a molecule

Answer

Energy difference between the reactants and products

Question 16

How does entropy relate to the level of disorder in a system?

Accepted Answer

Entropy increases with increasing disorder.

Answer

Entropy decreases with increasing disorder.

Answer

Entropy is unaffected by the level of disorder.

Question 17

Which of the following is the accepted SI unit of energy?

Accepted Answer

Joule

Answer

Calorie

Answer

Electronvolt

Answer

British Thermal Unit

Question 18

The entropy of a system is a measure of its:

Accepted Answer

Disorder

Answer

Order

Answer

Energy

Answer

Temperature

Question 19

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

Accepted Answer

Catalyst

Answer

Temperature

Answer

Pressure

Answer

Initial concentration of reactants

Question 20

The activation energy of a reaction is the:

Accepted Answer

Minimum amount of energy required for a reaction to occur

Answer

Maximum amount of energy released in a reaction

Answer

Change in energy between reactants and products

Answer

Rate at which a reaction proceeds

Question 21

The Hess cycle can be used to calculate:

Accepted Answer

Enthalpy changes of reactions

Answer

Entropy changes of reactions

Answer

Free energy changes of reactions

Answer

Equilibrium constants of reactions

Question 22

Which of the following is the correct unit for the enthalpy change of a reaction?

Accepted Answer

Kilojoules per mole (kJ/mol)

Answer

Joules (J)

Answer

Moles per joule (mol/J)

Answer

Joules per Kelvin (J/K)

Question 23

Which of the following factors does NOT affect the entropy of a system?

Accepted Answer

Mass of the system

Answer

Temperature

Answer

Pressure

Answer

Volume

Question 24

A spontaneous reaction is one that:

Accepted Answer

Has a negative free energy change

Answer

Has a positive free energy change

Answer

Is in equilibrium

Answer

Requires the addition of energy

Question 25

A catalyst in a chemical reaction:

Accepted Answer

Lowers the activation energy of the reaction

Answer

Alters the enthalpy change of the reaction

Answer

Alters the entropy change of the reaction

Answer

Affects the equilibrium constant of the reaction

Question 26

According to the Third Law of Thermodynamics, the standard molar entropy of a perfect crystal at 0 K is:

Accepted Answer

0 J/mol K

Answer

Positive

Answer

Negative

Answer

Cannot be determined

Question 27

The standard enthalpy change of formation is defined as:

Accepted Answer

The enthalpy change when 1 mol of a substance is formed from its elements in their standard states at 298 K and 1 bar

Answer

The enthalpy change when 1 g of a substance is formed from its elements in their standard states at 298 K and 1 bar

Answer

The enthalpy change when 1 L of a substance is formed from its elements in their standard states at 298 K and 1 bar

Answer

The enthalpy change when 1 mol of a substance is formed from its ions in their standard states at 298 K and 1 bar

Question 28

A spontaneous process is one that:

Accepted Answer

Has a negative Gibbs free energy change

Answer

Releases heat to the surroundings

Answer

Absorbs heat from the surroundings

Answer

Has a positive Gibbs free energy change

Question 29

The equilibrium constant for a reaction is:

Accepted Answer

The ratio of the products to the reactants at equilibrium

Answer

The ratio of the reactants to the products at equilibrium

Answer

The value of the Gibbs free energy change at equilibrium

Answer

The value of the enthalpy change at equilibrium

Question 30

Which of the following is NOT a type of catalyst?

Accepted Answer

Radioactive

Answer

Homogeneous

Answer

Heterogeneous

Answer

Biological

Question 31

A consequence of a collision between two reactant molecules is the:

Accepted Answer

Formation of an activated complex

Answer

Formation of a product

Answer

Release of energy

Answer

Absorption of energy

Question 32

The activation energy of a reaction is:

Accepted Answer

The minimum amount of energy that is required for a reaction to occur

Answer

The maximum amount of energy that is released in a reaction

Answer

The average amount of energy that is released in a reaction

Answer

The difference between the enthalpy change of the reaction and the enthalpy change of activation

Question 33

A measure of the disorder of a system is called:

Accepted Answer

Entropy

Answer

Enthalpy

Answer

Free energy

Answer

Gibbs free energy

Question 34

For exothermic reactions, what is the sign of the enthalpy change?

Accepted Answer

Negative

Answer

Positive

Answer

Zero

Answer

Varies with temperature

Question 35

How is the spontaneity of a reaction related to the free energy change?

Accepted Answer

A negative free energy change indicates a spontaneous reaction.

Answer

A positive free energy change indicates a spontaneous reaction.

Answer

Free energy change is unrelated to spontaneity.

Answer

Free energy change only determines the direction of the reaction.

Question 36

Define the enthalpy change of combustion for a hydrocarbon.

Accepted Answer

Heat released when one mole of the hydrocarbon reacts completely with oxygen

Answer

Heat absorbed when one mole of the hydrocarbon reacts completely with oxygen

Answer

Heat released when the hydrocarbon burns incompletely

Answer

Heat absorbed when the hydrocarbon burns incompletely

Question 37

Which of the following reactions is spontaneous?

Accepted Answer

A reaction with a negative enthalpy change and a positive entropy change

Answer

A reaction with a positive enthalpy change and a negative entropy change

Answer

A reaction with a negative enthalpy change and a negative entropy change

Answer

A reaction with a positive enthalpy change and a positive entropy change

Question 38

The equilibrium constant for a reaction is:

Accepted Answer

The ratio of the concentrations of the products to the concentrations of the reactants at equilibrium

Answer

The ratio of the enthalpy change of the reaction to the entropy change of the reaction

Answer

The Gibbs free energy change of the reaction at equilibrium

Answer

The temperature at which the reaction is in equilibrium

Question 39

The activation energy of a reaction is:

Accepted Answer

The minimum amount of energy that must be supplied to a reaction in order for it to occur

Answer

The maximum amount of energy that can be released by a reaction

Answer

The equilibrium constant of a reaction

Answer

The Gibbs free energy change of a reaction at equilibrium

Question 40

Which of the following is a catalyst?

Accepted Answer

A substance that increases the rate of a reaction without being consumed

Answer

A substance that decreases the rate of a reaction without being consumed

Answer

A substance that is consumed in a reaction

Answer

A substance that is produced in a reaction

Question 41

The change in enthalpy of a reaction at constant pressure is equal to:

Accepted Answer

The heat released by the reaction

Answer

The heat absorbed by the reaction

Answer

The change in Gibbs free energy of the reaction

Answer

The change in entropy of the reaction

Question 42

The change in entropy of a reaction is equal to:

Accepted Answer

The change in disorder of the system

Answer

The change in energy of the system

Answer

The change in volume of the system

Answer

The change in temperature of the system

Question 43

What is the standard unit of enthalpy change?

Accepted Answer

Kilojoules per mole

Answer

Joules

Answer

Calories

Answer

Electronvolts

Question 44

A chemical reaction with a negative change in enthalpy is classified as:

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Spontaneous

Answer

Equilibrium

Question 45

Select the equation used to calculate the Gibbs free energy change (ΔG):

Accepted Answer

ΔG = ΔH - TΔS

Answer

ΔG = ΔS - TΔH

Answer

ΔG = TΔS - ΔH

Answer

ΔG = ΔH + TΔS

Question 46

The equilibrium constant for a chemical reaction represents:

Accepted Answer

The ratio of products to reactants at equilibrium

Answer

The ratio of reactants to products at equilibrium

Answer

The value of ΔG at equilibrium

Answer

The value of ΔH at equilibrium

Question 47

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

Accepted Answer

Zero

Answer

Positive

Answer

Negative

Answer

Variable

Question 48

Which of the following is NOT a type of bond enthalpy?

Accepted Answer

Average bond enthalpy

Answer

C-C bond enthalpy

Answer

O-H bond enthalpy

Answer

Lattice enthalpy

Question 49

What is the sign of the entropy change for the reaction: 2H2O(l) → 2H2(g) + O2(g)?

Accepted Answer

Positive

Answer

Negative

Answer

Zero

Answer

Cannot be determined from the given information

Question 50

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

Accepted Answer

Identity of the reactants

Answer

Temperature

Answer

Pressure

Answer

Concentration of reactants

Question 51

If the Gibbs free energy change for a reaction is negative, what does this indicate about the spontaneity of the reaction under standard conditions?

Accepted Answer

The reaction is spontaneous

Answer

The reaction is non-spontaneous

Answer

The reaction is at equilibrium

Answer

The reaction is only spontaneous at high temperatures

Question 52

Which of the following statements about the enthalpy change of a reaction is true?

Accepted Answer

It can be positive or negative

Answer

It is always positive

Answer

It is always negative

Answer

It is zero for all reactions

Question 53

The activation energy of a reaction is defined as:

Accepted Answer

The energy difference between the reactants and the transition state

Answer

The energy difference between the transition state and the products

Answer

The energy difference between the reactants and the products

Answer

The energy required to break bonds in the reactants

Question 54

Which of the following reactions is likely to have the highest activation energy?

Accepted Answer

CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)

Answer

2H2(g) + O2(g) → 2H2O(l)

Answer

2NO(g) + O2(g) → 2NO2(g)

Answer

H2(g) + Cl2(g) → 2HCl(g)

Question 55

Which of the following is NOT a characteristic of a catalyst?

Accepted Answer

A catalyst is consumed in the reaction

Answer

A catalyst increases the rate of a reaction

Answer

A catalyst lowers the activation energy of the reaction

Answer

A catalyst is specific to a particular reaction