Energy Changes in Chemical Reactions: Interactive Learning Quizzes

Question 1

The enthalpy change of a reaction at constant pressure is also known as the:

Accepted Answer

Heat of reaction

Answer

Internal energy change

Answer

Entropy change

Answer

Gibbs free energy change

Question 2

Hess's law states that:

Accepted Answer

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

Answer

The entropy change of a reaction is independent of the reaction pathway

Answer

The Gibbs free energy change of a reaction is independent of the reaction pathway

Answer

The internal energy change of a reaction is independent of the reaction pathway

Question 3

The entropy of a system is a measure of:

Accepted Answer

Disorderliness or randomness

Answer

Heat content

Answer

Enthalpy

Answer

Gibbs free energy

Question 4

A spontaneous reaction is one that:

Accepted Answer

Occurs with a decrease in free energy

Answer

Requires an input of energy to occur

Answer

Has a positive enthalpy change

Answer

Has a negative entropy change

Question 5

Which of the following processes involves the release of heat energy?

Accepted Answer

Combustion of methane

Answer

Melting of ice

Answer

Dissolution of sugar in water

Answer

Evaporation of water

Question 6

The enthalpy change of a chemical reaction is defined as:

Accepted Answer

The difference in energy between the reactants and products

Answer

The heat absorbed or released by the reaction

Answer

The amount of energy required to break bonds

Answer

The maximum amount of work that can be done by the reaction

Question 7

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

Accepted Answer

Volume of the reaction vessel

Answer

Temperature

Answer

Pressure

Answer

Identity of the reactants

Question 8

Hess's law states that:

Accepted Answer

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

Answer

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

Answer

The entropy change of a reaction is equal to the sum of the entropy changes of its individual steps

Answer

The Gibbs free energy change of a reaction is equal to the sum of the Gibbs free energy changes of its individual steps

Question 9

Which of the following reactions is an endothermic process?

Accepted Answer

Photosynthesis

Answer

Combustion of propane

Answer

Neutralization of hydrochloric acid with sodium hydroxide

Answer

Respiration

Question 10

The enthalpy of formation of a substance refers to:

Accepted Answer

The enthalpy change when 1 mole of the substance is formed from its constituent elements

Answer

The enthalpy change when 1 mole of the substance is burned

Answer

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

Answer

The enthalpy change when 1 mole of the substance is vaporized

Question 11

Which of the following systems is considered a closed system?

Accepted Answer

A beaker of water with a lid

Answer

A car engine

Answer

A plant leaf

Answer

An open flask of water

Question 12

Which statement accurately describes an exothermic reaction?

Accepted Answer

It releases heat to the surroundings.

Answer

It absorbs heat from the surroundings.

Answer

It has a positive enthalpy change.

Answer

It has a negative enthalpy change.

Question 13

An endothermic reaction is characterized by:

Accepted Answer

Absorbing heat from the surroundings.

Answer

Releasing heat to the surroundings.

Answer

A positive entropy change.

Answer

A negative entropy change.

Question 14

The standard unit for expressing enthalpy change is:

Accepted Answer

Joules per mole (J/mol)

Answer

Degrees Celsius (°C)

Answer

Grams per mole (g/mol)

Answer

Liters per mole (L/mol)

Question 15

According to Hess's law:

Accepted Answer

The enthalpy change of a reaction equals the sum of the enthalpy changes of its individual steps.

Answer

The enthalpy change of a reaction is unaffected by the pathway taken.

Answer

The entropy change of a reaction equals the sum of the entropy changes of its individual steps.

Answer

The Gibbs free energy change of a reaction equals the sum of the Gibbs free energy changes of its individual steps.

Question 16

The enthalpy change for the combustion of methane is -890 kJ/mol. This value indicates:

Accepted Answer

The release of 890 kJ of heat when 1 mole of methane is combusted.

Answer

The absorption of 890 kJ of heat when 1 mole of methane is combusted.

Answer

The difference in energy between the reactants and products of the combustion reaction.

Answer

The activation energy required for the combustion reaction.

Question 17

Which is a potential application of Hess's law?

Accepted Answer

Calculating the enthalpy change of an indirect reaction.

Answer

Determining the feasibility of a reaction.

Answer

Predicting the products of a reaction.

Answer

Measuring the activation energy of a reaction.

Question 18

Define enthalpy change for a given reaction.

Accepted Answer

Heat absorbed or released by the reaction at constant pressure

Answer

Energy difference between reactants and products

Answer

Total energy released by the reaction

Answer

Activation energy required for the reaction

Question 19

Identify the application of Hess's law:

Accepted Answer

Calculating a reaction's enthalpy change using enthalpy changes of its component reactions

Answer

Predicting reaction products based on reactants

Answer

Determining reaction rates

Answer

Measuring equilibrium constants

Question 20

Identify the experiment used for calorimetry:

Accepted Answer

Measuring temperature change during reactions

Answer

Determining reaction rates

Answer

Identifying reaction products

Answer

Calculating equilibrium constants

Question 21

Define a spontaneous reaction.

Accepted Answer

Occurs without external energy input

Answer

Requires external energy input

Answer

Reaches equilibrium

Answer

Is reversible

Question 22

What is the enthalpy change, ΔH, for a reaction that releases heat into the surroundings?

Accepted Answer

ΔH < 0   (Negative enthalpy change, exothermic)

Answer

ΔH = 0   (Zero enthalpy change)

Answer

ΔH > 0   (Positive enthalpy change, endothermic)

Answer

ΔH cannot be determined from the given information

Question 23

Which of the following reactions is an example of an **endothermic** reaction?

Accepted Answer

Condensation of water vapor (H2O) to liquid water

Answer

Burning of methane (CH4) in air

Answer

Dissolution of sodium hydroxide (NaOH) in water

Answer

Neutralization of an acid with a base

Question 24

What is the SI unit of enthalpy change?

Accepted Answer

Kilojoule per mole (kJ/mol)

Answer

Joule (J)

Answer

Calorie (cal)

Answer

Electronvolt (eV)

Question 25

Which of the following processes is ALWAYS exothermic?

Accepted Answer

Combustion

Answer

Melting

Answer

Evaporation

Answer

Sublimation

Question 26

Which of the following is a unit of energy?

Accepted Answer

Joule

Answer

Kelvin

Answer

Mole

Answer

Celsius

Question 27

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

Accepted Answer

Zero

Answer

Positive

Answer

Negative

Answer

Variable

Question 28

Identify the exothermic reaction:

Accepted Answer

2H2(g) + O2(g) → 2H2O(l)

Answer

N2(g) + 3H2(g) → 2NH3(g)

Answer

CO2(g) + H2O(l) → H2CO3(aq)

Answer

CaCO3(s) → CaO(s) + CO2(g)

Question 29

Which of the following is a characteristic of an exothermic reaction?

Accepted Answer

Energy is released into the surroundings.

Answer

Temperature of the surroundings decreases.

Answer

Enthalpy change is positive.

Answer

Reactants have lower energy than products.

Question 30

The enthalpy change of a reaction is a measure of the:

Accepted Answer

Heat transferred to or from the surroundings at constant pressure.

Answer

Total amount of energy stored in the products.

Answer

Change in volume of the system.

Question 31

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

Accepted Answer

Is independent of the pathway taken.

Answer

Is equal to the sum of the activation energies of the individual steps in the pathway.

Answer

Can be predicted only if the reaction is carried out under standard conditions.

Answer

Depends on the initial and final temperatures of the reaction.

Question 32

Which of the following reactions is most likely to be endothermic?

Accepted Answer

2NH3(g) → N2(g) + 3H2(g)

Answer

Fe2O3(s) + 2Al(s) → Al2O3(s) + 2Fe(s)

Answer

C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(l)

Answer

CaO(s) + H2O(l) → Ca(OH)2(aq)

Question 33

The following reaction is exothermic: A(g) + B(g) → C(g) + D(g). Which of the following graphs best represents the energy profile of this reaction?

Accepted Answer

Graph with a negative gradient (downward slope) from A+B reactants to C+D products.

Answer

Graph with a positive gradient (upward slope) from A+B reactants to C+D products.

Answer

Graph with a horizontal line from A+B reactants to C+D products.

Question 34

Which of the following factors affects the activation energy of a reaction?

Accepted Answer

Nature of the reactants.

Answer

Surface area of the reactants.

Answer

Temperature of the surroundings.

Answer

Concentration of the products.

Question 35

A reaction with a large negative enthalpy change is:

Accepted Answer

Exothermic.

Answer

Endothermic.

Answer

Thermoneutral.

Question 36

Which of the following processes results in a decrease in entropy?

Accepted Answer

A liquid freezing to a solid.

Answer

A chemical reaction reaching equilibrium.

Answer

A solid dissolving in water.

Answer

A gas expanding into a larger volume.

Question 37

Which of the following is a consequence of increasing the concentration of a reactant in a reaction?

Accepted Answer

Rate of the forward reaction increases.

Answer

Activation energy is lowered.

Answer

Enthalpy change becomes less negative.

Answer

Equilibrium constant decreases.

Question 38

Define an exothermic reaction.

Accepted Answer

A chemical reaction that releases heat into the surroundings.

Answer

A chemical reaction that absorbs heat from the surroundings.

Answer

A chemical reaction that has no change in temperature.

Question 39

In an endothermic reaction, the change in enthalpy is:

Accepted Answer

Positive

Answer

Negative

Answer

Unpredictable

Answer

Zero

Question 40

Hess's law can be used to:

Accepted Answer

Calculate the enthalpy change of a reaction that cannot be measured directly.

Answer

Predict the products of a reaction.

Answer

Determine the rate of a reaction.

Question 41

A reaction with a negative enthalpy change is:

Accepted Answer

Exothermic

Answer

Isothermal

Answer

Endothermic

Answer

Adiabatic

Question 42

Define the enthalpy change of combustion.

Accepted Answer

The enthalpy change when a substance reacts completely with oxygen.

Answer

The enthalpy change when a substance reacts with water.

Answer

The enthalpy change when a substance is formed from its elements.

Question 43

An isothermal reaction is a reaction that occurs with:

Accepted Answer

No change in enthalpy

Answer

Negative enthalpy change

Answer

Unpredictable enthalpy change

Answer

Positive enthalpy change