Chemical Reactions and Equilibrium: Master the Energetics and Equilibria Concepts

Question 1

The enthalpy change of a reaction is defined as:

Accepted Answer

The heat absorbed or released during the reaction at constant pressure

Answer

The difference in potential energy between the reactants and products

Answer

The change in free energy of the reaction

Answer

The entropy change of the reaction

Question 2

Hess's law states that:

Accepted Answer

The enthalpy change of a reaction is independent of the pathway taken

Answer

The entropy change of a reaction is always positive

Answer

The free energy change of a reaction is always negative

Answer

The equilibrium constant of a reaction is always greater than 1

Question 3

Hess's law can be used to determine the enthalpy change of a reaction that **cannot be measured directly**. True or False?

Accepted Answer

True

Answer

False

Question 4

Le Chatelier's principle can be used to predict the shift in equilibrium when a **reactant** is added. True or False?

Accepted Answer

True

Answer

False

Question 5

Free energy is a measure of the **spontaneity** of a reaction. True or False?

Accepted Answer

True

Answer

False

Question 6

Which of the following processes is exothermic?

Accepted Answer

Dissolving of sodium hydroxide in water

Answer

Melting of ice at 0 °C

Answer

Condensation of water vapour at 100 °C

Answer

Sublimation of solid carbon dioxide at -78 °C

Question 7

Which of the following techniques is used to measure the enthalpy change of a reaction?

Accepted Answer

Calorimetry

Answer

Spectroscopy

Answer

Titration

Answer

Chromatography

Question 8

What is the SI unit of entropy?

Accepted Answer

Joules per Kelvin per mole

Answer

Joules

Answer

Joules per mole

Answer

Kelvin per mole

Question 9

Hess's law states that:

Accepted Answer

The enthalpy change of a reaction pathway is equal to the sum of the enthalpy changes of the individual steps.

Answer

The enthalpy change of a reaction is always positive.

Answer

The enthalpy change of a reaction is always negative.

Answer

The enthalpy change of a reaction depends on the temperature and pressure.

Question 10

Which of the following factors increases the entropy of a system?

Accepted Answer

Dissolving a solid in water

Answer

Decreasing volume

Answer

Decreasing temperature

Answer

Decreasing pressure

Question 11

The free energy change for a reaction is:

Accepted Answer

The difference between the enthalpy change and the entropy change of the reaction.

Answer

The difference between the enthalpy change and the temperature change of the reaction.

Answer

Always positive.

Answer

Always negative.

Question 12

Which of the following equilibrium systems will shift to the reactant side when the  pressure is increased?

Accepted Answer

N₂ (g) + 3H₂ (g) <=> 2NH₃ (g)

Answer

2NO (g) + O₂ (g) <=> 2NO₂ (g)

Answer

CaCO₃ (s) <=> CaO (s) + CO₂ (g)

Question 13

The activation energy of a reaction is:

Accepted Answer

The minimum energy required for a reaction to occur.

Answer

The maximum energy released during a reaction.

Answer

The difference in enthalpy between the reactants and products.

Question 14

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 negative enthalpy change and a negative entropy change.

Answer

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

Answer

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

Question 15

Which of the following is a buffer solution?

Accepted Answer

A solution containing a weak acid and its conjugate base

Answer

A solution containing a strong acid and its conjugate base

Answer

A solution containing a strong base and its conjugate acid

Answer

A solution containing pure water

Question 16

The Gibbs free energy change of a reaction is the change in

Accepted Answer

Enthalpy minus the product of temperature and entropy

Answer

Entropy minus the product of temperature and enthalpy

Answer

Enthalpy plus the product of temperature and entropy

Answer

Entropy plus the product of temperature and enthalpy

Question 17

At equilibrium, the forward and reverse reactions occur at

Accepted Answer

The same rate, but in opposite directions

Answer

Different rates

Answer

Zero rate

Answer

Equal rates, in the same direction

Question 18

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

Accepted Answer

Negative

Answer

Positive

Answer

Zero

Answer

Cannot be determined

Question 19

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

Accepted Answer

Pressure

Answer

Enthalpy change

Answer

Entropy change

Answer

Temperature

Question 20

Which of the following is a measure of the randomness or disorder of a system?

Accepted Answer

Entropy

Answer

Enthalpy

Answer

Free energy

Answer

Gibbs free energy

Question 21

The equilibrium constant for a reaction is:

Accepted Answer

The ratio of products to reactants at equilibrium

Answer

The ratio of reactants to products at equilibrium

Answer

The difference between the concentrations of reactants and products

Answer

The rate constant for the forward reaction

Question 22

A reaction with a small equilibrium constant is:

Accepted Answer

Less likely to proceed to completion

Answer

More likely to proceed to completion

Answer

Independent of the initial concentrations

Answer

Always exothermic

Question 23

The Gibbs free energy change for a reaction is:

Accepted Answer

The change in free energy at constant temperature and pressure

Answer

The change in enthalpy at constant temperature

Answer

The change in entropy at constant temperature

Answer

The change in volume at constant temperature

Question 24

What is the standard enthalpy change of formation of water?

Accepted Answer

-285.8 kJ mol^-1

Answer

+285.8 kJ mol^-1

Answer

-85.2 kJ mol^-1

Answer

+85.2 kJ mol^-1

Question 25

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

Accepted Answer

Positive

Answer

Negative

Answer

Zero

Answer

Insufficient information provided

Question 26

What is the spontaneity criterion for a reaction?

Accepted Answer

ΔG < 0

Answer

ΔG > 0

Answer

ΔG = 0

Answer

ΔH > 0

Question 27

Which limitation applies to Hess's law?

Accepted Answer

Assumes enthalpy changes are additive

Answer

Only applies to gas phase reactions

Answer

Invalid for reactions involving solids

Answer

Requires highly accurate experimental data

Question 28

Which reaction exhibits the largest positive entropy change?

Accepted Answer

NH4Cl(s) → NH4+(aq) + Cl-(aq)

Answer

H2(g) + 1/2O2(g) → H2O(l)

Answer

2Na(s) + Cl2(g) → 2NaCl(s)

Answer

CO2(g) + CaO(s) → CaCO3(s)

Question 29

What is the equilibrium constant value for a system at equilibrium?

Accepted Answer

One

Answer

Zero

Answer

Greater than one

Answer

Less than one

Question 30

Which of the following is the standard enthalpy change of formation of water vapour at 298K?

Accepted Answer

-241.8 kJ mol^-1

Answer

0 kJ mol^-1

Answer

285.8 kJ mol^-1

Answer

241.8 kJ mol^-1

Question 31

The entropy change for the reaction A(g) → B(g) + C(g) is positive. What does this indicate about the reaction?

Accepted Answer

The reaction leads to an increase in disorder.

Answer

The reaction is exothermic.

Answer

The reaction is endothermic.

Answer

The reaction leads to a decrease in disorder.

Question 32

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

Accepted Answer

Volume of the reaction vessel

Answer

Enthalpy change

Answer

Entropy change

Answer

Temperature

Question 33

Which of the following reactions will shift to the right when the temperature is increased?

Accepted Answer

Endothermic reaction

Answer

Exothermic reaction

Answer

Neither exothermic nor endothermic reaction

Answer

Both exothermic and endothermic reactions

Question 34

The activation energy of a reaction is:

Accepted Answer

The minimum amount of energy required for a reaction to occur.

Answer

The maximum amount of energy released in a reaction.

Answer

The difference in energy between the reactants and products.

Answer

The rate at which a reaction occurs.

Question 35

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 not involved in a reaction

Question 36

Entropy is a measure of:

Accepted Answer

The disorder or randomness of a system

Answer

The energy of a system

Answer

The free energy of a system

Answer

The enthalpy of a system

Question 37

The equilibrium constant for a reaction is:

Accepted Answer

A measure of the extent to which the reaction proceeds

Answer

A measure of the rate of the reaction

Answer

A measure of the spontaneity of the reaction

Answer

A measure of the enthalpy change of the reaction

Question 38

According to Le Chatelier's principle, increasing the pressure of a reaction that involves gases will:

Accepted Answer

Shift the equilibrium to the side with more moles of gas

Answer

Shift the equilibrium to the side with fewer moles of gas

Answer

Not affect the equilibrium position

Answer

Increase the rate of the forward reaction

Question 39

What is the value of the equilibrium constant for a reaction that proceeds to completion?

Accepted Answer

∞

Answer

0

Answer

1

Answer

10

Question 40

Which of the following is the correct expression for the entropy change of a reaction?

Accepted Answer

ΔS = S(products) - S(reactants)

Answer

ΔS = S(reactants) - S(products)

Answer

ΔS = H - T

Answer

ΔS = G - H

Question 41

Which of the following measures the randomness or disorder of a system?

Accepted Answer

Entropy

Answer

Enthalpy

Answer

Free energy

Answer

Internal energy

Question 42

A spontaneous reaction is one that:

Accepted Answer

Has a negative free energy change

Answer

Has a positive free energy change

Answer

Has a zero free energy change

Answer

Requires the input of energy

Question 43

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

Accepted Answer

Type of catalyst used

Answer

Temperature

Answer

Pressure

Answer

Concentration of reactants

Question 44

A reaction with a large negative ΔG°:

Accepted Answer

Is spontaneous

Answer

Is non-spontaneous

Answer

Is at equilibrium

Answer

Is dependent on temperature

Question 45

The equation for the Gibbs free energy change is:

Accepted Answer

ΔG = ΔH - TΔS

Answer

ΔG = ΔH + TΔS

Answer

ΔG = -ΔH + TΔS

Answer

ΔG = -ΔH - TΔS

Question 46

A reaction that releases heat is referred to as:

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Isothermal

Answer

Adiabatic

Question 47

Which of the following is directly related to the spontaneity of a reaction?

Accepted Answer

Free energy change

Answer

Enthalpy change

Answer

Entropy change

Answer

Equilibrium constant

Question 48

What is the equilibrium constant expression for the reaction: 2NO(g) + O2(g) ⇌ 2NO2(g)?

Accepted Answer

K = [NO2]² / [NO]²[O2]

Answer

K = [NO]²[O2] / [NO2]²

Answer

K = [NO]² + [O2]² / [NO2]²

Answer

K = [NO2]² - [NO]² / [O2]

Question 49

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

Accepted Answer

Zero

Answer

Positive

Answer

Negative

Answer

Dependent on temperature