Thermochemistry: Energy Changes in Chemical Reactions Quiz

Question 1

The enthalpy change of a system is positive for an endothermic reaction. True or False?

Accepted Answer

True

Answer

False

Question 2

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

Accepted Answer

Pressure

Answer

Enthalpy change

Answer

Entropy change

Answer

Temperature

Question 3

Which of the following will NOT shift the equilibrium position of a reaction to the right?

Accepted Answer

Increasing the concentration of products

Answer

Increasing the temperature

Answer

Adding a catalyst

Answer

Increasing the concentration of reactants

Question 4

The rate of a reaction is always proportional to the activation energy. True or False?

Accepted Answer

False

Answer

True

Question 5

The Gibbs free energy is a useful function to determine the spontaneity of a reaction. True or False?

Accepted Answer

True

Answer

False

Question 6

Which of the following is a strong electrolyte?

Accepted Answer

NaCl

Answer

CH3COOH

Answer

NH3

Answer

C6H12O6

Question 7

Calculate the change in enthalpy (ΔH) for a reaction using the correct formula:

Accepted Answer

ΔH = H(products) - H(reactants)

Answer

ΔH = H(reactants) - H(products)

Answer

ΔH = S(products) - S(reactants)

Answer

ΔH = G(products) - G(reactants)

Question 8

Identify the criterion that determines whether a reaction is spontaneous or non-spontaneous:

Accepted Answer

ΔG

Answer

ΔH

Answer

ΔS

Answer

ΔT

Question 9

What is the standard enthalpy change for a reaction at equilibrium with an equilibrium constant of 1?

Accepted Answer

0 kJ/mol

Answer

Positive kJ/mol

Answer

Negative kJ/mol

Answer

Cannot be determined from the given information

Question 10

Which factor does NOT influence the rate of a chemical reaction?

Accepted Answer

ΔG

Answer

Temperature

Answer

Concentration of reactants

Answer

Surface area of reactants

Question 11

Establish the relationship between ΔH and ΔS for a reaction that has reached equilibrium:

Accepted Answer

ΔH = TΔS

Answer

ΔH > TΔS

Answer

ΔH < TΔS

Answer

ΔH = 0

Question 12

Identify the unit of entropy:

Accepted Answer

Joules per Kelvin

Answer

Calories per Kelvin

Answer

Kilojoules per mole

Answer

Liters per mole

Question 13

Determine the sign of ΔG for a non-spontaneous reaction:

Accepted Answer

Positive

Answer

Negative

Answer

Zero

Answer

Cannot be determined from the given information

Question 14

Select the reaction with the most negative ΔG value:

Accepted Answer

D + E → F (ΔH = -20 kJ/mol, ΔS = -10 J/mol-K)

Answer

A + B → C (ΔH = +10 kJ/mol, ΔS = +20 J/mol-K)

Answer

G + H → I (ΔH = -5 kJ/mol, ΔS = +15 J/mol-K)

Answer

J + K → L (ΔH = +15 kJ/mol, ΔS = +30 J/mol-K)

Question 15

Which of the following is NOT a state function?

Accepted Answer

Work

Answer

Enthalpy

Answer

Entropy

Answer

Free energy

Question 16

A reaction with a negative enthalpy change is referred to as:

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Spontaneous

Answer

Athermic

Question 17

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

Accepted Answer

Type of solvent

Answer

Temperature

Answer

Pressure

Answer

Concentration of reactants and products

Question 18

Standard enthalpy of formation is defined as:

Accepted Answer

The enthalpy change when 1 mole of a substance is formed from its elements in their **standard states**

Answer

The enthalpy change when 1 mole of a substance is formed from its elements at any conditions

Answer

The enthalpy change when 1 mole of a substance is burned in oxygen

Answer

The enthalpy change when 1 mole of a substance is dissolved in water

Question 19

Which of the following reactions is most likely to be spontaneous at standard conditions?

Accepted Answer

ΔH = -10 kJ/mol, ΔS = +20 J/(mol·K)

Answer

ΔH = +10 kJ/mol, ΔS = -20 J/(mol·K)

Answer

ΔH = +10 kJ/mol, ΔS = +20 J/(mol·K)

Answer

ΔH = -10 kJ/mol, ΔS = -20 J/(mol·K)

Question 20

Which of the following is a unit of entropy?

Accepted Answer

Joules per Kelvin

Answer

Joules

Answer

Degrees Celsius

Answer

Calories per gram

Question 21

The standard molar entropy of a perfect crystal at absolute zero is:

Accepted Answer

0 J/(mol·K)

Answer

1 J/(mol·K)

Answer

2 J/(mol·K)

Answer

3 J/(mol·K)

Question 22

Consider a reaction with ΔH = +10 kJ/mol and ΔS = -50 J/mol·K. Determine the spontaneity of the reaction at 298 K. Explain your reasoning.

Accepted Answer

Nonspontaneous

Answer

Spontaneous

Answer

Cannot be determined without more information

Answer

Spontaneous at high temperatures

Question 23

In a reversible isothermal process, what is the change in entropy of the system?

Accepted Answer

ΔS = 0

Answer

ΔS = Q/T

Answer

ΔS = -Q/T

Question 24

Which statement accurately defines enthalpy (H)?

Accepted Answer

Heat released or absorbed in a reaction at constant pressure

Answer

Total energy stored within a system

Answer

Force driving chemical reactions forward

Answer

Measure of disorder within a system

Question 25

Classify a reaction that releases heat into its surroundings:

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Adiabatic

Answer

Neither exothermic nor endothermic

Question 26

The formula for calculating the change in free energy (ΔG) of a reaction is:

Accepted Answer

ΔH - TΔS

Answer

ΔH + TΔS

Answer

TΔS - ΔH

Answer

ΔS - ΔH

Question 27

Which process occurs spontaneously?

Accepted Answer

ΔG < 0

Answer

ΔG > 0

Answer

ΔG = 0

Answer

ΔH < 0 and ΔS > 0

Question 28

The equilibrium constant (Keq) of a reaction can be determined using:

Accepted Answer

ΔG/RT

Answer

ΔH/RT

Answer

-ΔS/R

Answer

ΔH - TΔS

Question 29

Which reaction type is NOT favored by increased temperature?

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Reaction with ΔH = 0

Answer

Reaction with ΔS > 0

Question 30

According to Hess's law, the:

Accepted Answer

Enthalpy change of a reaction is independent of the reaction pathway.

Answer

Entropy change of a reaction equals the sum of entropy changes in individual steps.

Answer

Free energy change of a reaction equals the enthalpy change minus the product of temperature and entropy change.

Answer

Equilibrium constant of a reaction is proportional to the square of the reactant concentrations.

Question 31

Which of the following is the standard state for enthalpy, temperature, and pressure?

Accepted Answer

1 atm and 298 K

Answer

1 atm and 0 K

Answer

0.1 atm and 298 K

Answer

0.1 atm and 0 K

Question 32

The enthalpy change for a reaction is defined as the:

Accepted Answer

Difference between the enthalpies of the products and reactants

Answer

Sum of the enthalpies of the products and reactants

Answer

Enthalpy of the reactants multiplied by their stoichiometric coefficients

Question 33

Entropy is defined as a measure of:

Accepted Answer

Disorder or randomness of a system

Answer

Change in volume of a system

Answer

Change in temperature of a system

Question 34

The free energy change for a reaction is the:

Accepted Answer

Maximum amount of work that can be done by the reaction

Answer

Change in enthalpy of the reaction

Answer

Change in entropy of the reaction

Question 35

Which of the following conditions will result in a spontaneous reaction?

Accepted Answer

Negative free energy change

Answer

Positive free energy change

Answer

Zero free energy change

Answer

Positive enthalpy change

Question 36

The equilibrium constant for a reaction is the:

Accepted Answer

Ratio of the concentrations of products to reactants at equilibrium

Answer

Change in concentration of reactants over time

Answer

Rate of the forward reaction

Question 37

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

Accepted Answer

Volume

Answer

Concentration

Answer

Pressure

Answer

Temperature

Question 38

Le Chatelier's principle states that:

Accepted Answer

If a stress is applied to a system at equilibrium, the system will shift in a direction that relieves the stress

Answer

The equilibrium constant of a reaction is constant

Question 39

Which of the following processes releases energy in the form of heat?

Accepted Answer

Combustion of methane

Answer

Melting of ice

Answer

Dissolving salt in water

Answer

Photosynthesis

Question 40

In an irreversible process for a closed system, what happens to the entropy?

Accepted Answer

Increases

Answer

Remains constant

Answer

Unpredictable

Answer

Decreases

Question 41

Which reaction exhibits the greatest positive entropy change?

Accepted Answer

A(s) → A(g)

Answer

A(g) → A(l)

Answer

A(l) → A(s)

Question 42

Which of the following is NOT a characteristic of a state function?

Accepted Answer

It is path dependent.

Answer

It is an extensive property.

Answer

It depends only on the initial and final states.

Answer

It can be used to calculate the change in a property of a system.

Question 43

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

Accepted Answer

The heat transferred into or out of the system.

Answer

The heat transferred into or out of the system at constant volume.

Answer

The change in internal energy of the system.

Answer

The change in entropy of the system.

Question 44

Which of the following reactions is exothermic?

Accepted Answer

Combustion of methane

Answer

Evaporation of water

Answer

Dissolution of NaCl in water

Answer

Melting of ice

Question 45

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

Accepted Answer

Entropy

Answer

Enthalpy

Answer

Gibbs free energy

Answer

Internal energy

Question 46

The Gibbs free energy change of a reaction is equal to:

Accepted Answer

The maximum amount of non-expansion work that can be obtained from the reaction at constant temperature and pressure.

Answer

The change in enthalpy of the reaction at constant pressure.

Answer

The change in entropy of the reaction at constant temperature.

Question 47

The standard enthalpy of formation of a compound is:

Accepted Answer

The enthalpy change of its formation from its constituent elements in their standard states.

Answer

The enthalpy change of its decomposition into its constituent elements.

Answer

The enthalpy change of its combustion.

Question 48

The enthalpy change for a reaction is -50 kJ/mol. What type of reaction is this?

Accepted Answer

Exothermic

Answer

Isothermal

Answer

Endothermic

Answer

Adiabatic

Question 49

Which of the following is NOT a state function?

Accepted Answer

Heat

Answer

Gibbs Free Energy

Answer

Enthalpy

Answer

Entropy

Question 50

A reaction with a positive enthalpy change and a positive entropy change will be spontaneous at:

Accepted Answer

High temperatures

Answer

Low temperatures

Answer

All temperatures

Answer

No temperature

Question 51

Calculate the standard free energy change (ΔG°) for the following reaction at 298 K:

2NO(g) + O2(g) → 2NO2(g)

Given that ΔH° = -114.1 kJ/mol and ΔS° = -146.5 J/mol·K.

Accepted Answer

-70.5 kJ/mol

Answer

-114.1 kJ/mol

Answer

146.5 kJ/mol

Answer

260.6 kJ/mol

Question 52

What is the enthalpy change for the following reaction, given the following standard enthalpy of formation values?

CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)

ΔHf°(CH4) = -74.8 kJ/mol, ΔHf°(CO2) = -393.5 kJ/mol, ΔHf°(H2O) = -285.8 kJ/mol

Accepted Answer

-890.3 kJ/mol

Answer

-571.6 kJ/mol

Answer

890.3 kJ/mol

Question 53

The standard enthalpy of combustion for methane (CH4) is -890.3 kJ/mol. Calculate the enthalpy change for the combustion of 2 moles of methane.

Accepted Answer

-1780.6 kJ/mol

Answer

-890.3 kJ/mol

Answer

1780.6 kJ/mol

Answer

890.3 kJ/mol

Question 54

The reaction 2NO2(g) → N2O4(g) has a negative entropy change. Why is this?

Accepted Answer

The reaction results in a decrease in the number of gas molecules

Answer

The reaction is endothermic

Answer

The reaction is exothermic

Question 55

A process is considered spontaneous if:

Accepted Answer

ΔG is negative

Answer

ΔG is positive

Answer

ΔS is positive

Answer

ΔH is negative

Question 56

The standard entropy of a substance is:

Accepted Answer

The entropy of the substance at 1 atm and 298 K

Answer

The entropy change when the substance is formed from its elements

Answer

The entropy of the substance at its boiling point

Question 57

Which of the following is an example of a process that increases entropy?

Accepted Answer

Melting of ice

Answer

Condensation of steam

Answer

Freezing of water

Answer

Formation of a precipitate