Thermochemistry: Heat and Chemical Reactions - Online Learning Quizzes

Question 1

What is the primary factor that determines the enthalpy change of a chemical reaction?

Accepted Answer

Nature of reactants and products

Answer

Temperature

Answer

Pressure

Answer

Concentration of reactants

Question 2

Which of the following describes a spontaneous exothermic process?

Accepted Answer

(A) Heat is released to the surroundings, and the process occurs without external input.

Answer

(B) Heat is absorbed from the surroundings, and the process occurs without external input.

Answer

(C) Heat is released to the surroundings, but external input is needed for the process to occur.

Answer

(D) Heat is absorbed from the surroundings, but external input is needed for the process to occur.

Question 3

In the combustion reaction of methane (CH4), the standard enthalpy change is -890 kJ/mol. If 1.00 mol of CH4 is burned under standard conditions, how much energy is released as heat?

Accepted Answer

-890 kJ

Answer

445 kJ

Answer

1780 kJ

Answer

0 kJ

Question 4

For an exothermic reaction at constant pressure, what is the sign of ΔH?

Accepted Answer

Negative

Answer

Positive

Answer

Zero

Answer

Temperature-dependent

Question 5

Which process releases heat to the surroundings?

Accepted Answer

Combustion of methane

Answer

Melting of ice

Answer

Evaporation of water

Answer

Dissolution of salt in water

Question 6

In thermochemistry, what is the precise definition of enthalpy change?

Accepted Answer

The difference in enthalpy between the final and initial states of a system, regardless of the reaction pathway.

Answer

A negative value for exothermic reactions, indicating heat absorption by the system.

Answer

Equivalent to internal energy change, representing the total energy of the system.

Answer

A measure of the system's disorder or randomness.

Question 7

Which process maintains a constant temperature due to continuous heat exchange with its surroundings?

Accepted Answer

Isothermal

Answer

Adiabatic

Answer

Exothermic

Answer

Endothermic

Question 8

Define enthalpy in the context of thermodynamics.

Accepted Answer

Sum of internal energy and the product of pressure and volume

Answer

Heat transferred under constant pressure

Answer

Maximum work extracted at constant temperature and pressure

Answer

Entropy at constant volume

Question 9

Which process is non-spontaneous according to the Gibbs free energy equation?

Accepted Answer

Positive ΔH and negative ΔS

Answer

Negative enthalpy change (ΔH) and positive entropy change (ΔS)

Answer

Negative ΔH and negative ΔS

Answer

Positive ΔH and positive ΔS

Question 10

A chemical reaction takes place at constant pressure, resulting in an enthalpy change of -50 kJ. What can be concluded about this reaction?

Accepted Answer

It releases 50 kJ of heat into the surroundings.

Answer

It absorbs 50 kJ of heat from the surroundings.

Answer

It occurs without any heat exchange with the surroundings.

Answer

The temperature of the surroundings increases by 50 K.

Question 11

Which of the following accurately describes enthalpy?

Accepted Answer

A measure of the heat content of a system

Accepted Answer

Is a state function

Answer

Can only change when heat is added or removed

Answer

Always has a positive value

Question 12

Which of the following correctly describes the relationship between enthalpy and entropy?

Accepted Answer

Enthalpy measures the heat content, while entropy measures the disorder.

Answer

Enthalpy and entropy are always directly proportional.

Answer

Enthalpy and entropy are never related.

Answer

Entropy measures the heat content, while enthalpy measures the disorder.

Question 13

Which of the following accurately describes enthalpy?

Accepted Answer

Enthalpy is a state function.

Accepted Answer

Enthalpy is an extensive property.

Answer

Enthalpy is always positive for exothermic reactions.

Question 14

In an adiabatic process, where heat exchange between the system and its surroundings is absent, which parameter remains constant?

Accepted Answer

Internal energy

Answer

Temperature

Answer

Pressure

Answer

Volume

Question 15

The reaction 2C(s) + O2(g) ---> 2CO(g) releases heat. What is the sign of the enthalpy change for this reaction?

Accepted Answer

Positive

Answer

Negative

Answer

Zero

Answer

Cannot be determined from the given information

Question 16

In an isobaric process within a closed system, if heat is released, what happens to the system's internal energy?

Accepted Answer

Decreases

Answer

Increases

Answer

Stays the same

Question 17

In an adiabatic process, what is the relationship between work done and internal energy change?

Accepted Answer

The work done by the system equals the change in internal energy of the system.

Answer

Heat is transferred between the system and the surroundings.

Answer

The temperature of the system remains constant.

Answer

Adiabatic processes are always reversible.

Question 18

In thermochemistry, exothermic reactions are characterized by which of the following enthalpy change (ΔH) patterns?

Accepted Answer

ΔH is always negative, signifying an enthalpy decrease.

Answer

ΔH is always positive, indicating an enthalpy increase.

Answer

ΔH does not provide information about heat flow in reactions.

Question 19

During an isothermal expansion of an ideal gas, how does its entropy change according to the second law of thermodynamics?

Accepted Answer

Increases

Answer

Decreases

Answer

Remains constant

Answer

Cannot be determined without additional information

Question 20

During complete combustion of a hydrocarbon in ample oxygen, what energy phenomenon typically accompanies the change in enthalpy?

Accepted Answer

Heat release

Answer

Electrical energy generation

Answer

Light emission

Question 21

Which of the following statements best describes a key characteristic of enthalpy?

Accepted Answer

Enthalpy is a state function that depends solely on the initial and final states of a system.

Answer

Enthalpy represents the maximum work a system can perform.

Answer

Enthalpy changes indicate whether a reaction is exothermic or endothermic.

Answer

Enthalpy is conserved in all chemical reactions.

Question 22

Which of the following accurately describes a key property of enthalpy?

Accepted Answer

Enthalpy is a state function, determined solely by the system's current state.

Answer

Enthalpy encompasses a system's total energy, including internal and kinetic components.

Answer

Enthalpy consistently decreases in exothermic reactions and increases in endothermic reactions.

Answer

Enthalpy and entropy are interchangeable concepts, both measuring energy dispersal within a system.

Question 23

In Hess's Law, which method is used to calculate the standard enthalpy change of a reaction?

Accepted Answer

Breaking the reaction into steps and adding their enthalpy changes

Answer

Assuming constant pressure and temperature

Answer

Measuring heat flow through calorimetry

Question 24

What is the SI unit of specific heat capacity, defined as the amount of heat energy needed to raise the temperature of 1 gram of a substance by 1 degree Celsius?

Accepted Answer

Joules per gram per degree Celsius (J/g/°C)

Answer

Calories per gram per degree Celsius (cal/g/°C)

Answer

Degrees Celsius per gram per joule (°C/g/J)

Question 25

Which process involves the release of energy from the system to the surroundings?

Accepted Answer

Combustion of methane

Answer

Evaporation of water

Answer

Melting of ice

Question 26

In an exothermic process, what occurs to the system's enthalpy?

Accepted Answer

Decreases

Answer

Increases

Answer

Remains constant

Question 27

How do enthalpy and entropy influence a reaction's spontaneity? Explain how these concepts guide predictions about reaction directionality, providing examples to illustrate your explanation.

Accepted Answer

Enthalpy and entropy both contribute to the spontaneity of a reaction, as reflected in the Gibbs free energy change (ΔG).

Accepted Answer

The spontaneity of a reaction is determined by the sign of the Gibbs free energy change (ΔG), with negative ΔG indicating spontaneity.

Answer

Entropy always favors spontaneous reactions, regardless of the enthalpy change.

Answer

Exothermic reactions are always spontaneous, while endothermic reactions are always non-spontaneous.

Question 28

Which of the following processes releases heat to the surroundings?

Accepted Answer

Burning of methane

Answer

Freezing of water

Answer

Dissolving of salt in water

Answer

Condensation of water vapor

Question 29

The randomness or disorder of a system is measured by:

Accepted Answer

Entropy

Answer

Internal energy

Answer

Enthalpy

Answer

Gibbs free energy

Question 30

The heat capacity of a substance represents its resistance to:

Accepted Answer

Temperature change

Answer

Phase change

Answer

Chemical change

Answer

Electrical current

Question 31

Which method can be used to calculate the enthalpy change of a reaction indirectly using enthalpies of formation?

Accepted Answer

Hess's Law

Answer

Kirchhoff's Law

Answer

Calorimetry

Answer

Spectroscopy

Question 32

A quantity that depends only on the initial and final states of a system, not on the path taken, is a:

Accepted Answer

State function

Answer

Path function

Answer

Extensive property

Answer

Intensive property

Question 33

The Carnot cycle operates between:

Accepted Answer

High and low temperature reservoirs

Answer

High and low pressure reservoirs

Answer

High and low volume reservoirs

Answer

High and low concentration reservoirs

Question 34

The Gibbs free energy is used to predict:

Accepted Answer

The spontaneity of a reaction

Answer

The equilibrium constant

Answer

The rate of a reaction

Answer

The enthalpy change of a reaction

Question 35

Which reaction releases heat when it occurs?

Accepted Answer

2H2 + O2 → 2H2O

Answer

CO2 + H2 → CO + H2O

Answer

N2 + 3H2 → 2NH3

Answer

C6H12O6 → 6CO2 + 6H2O

Question 36

The heat of vaporization is the amount of heat required to:

Accepted Answer

Convert a substance from a liquid to a gas

Answer

Raise the temperature of a substance

Answer

Convert a substance from a solid to a liquid

Answer

Convert a substance from a gas to a solid

Question 37

How do enthalpy changes provide valuable information about the mechanism of a multi-step reaction?

Accepted Answer

They provide insights into the relative stability of intermediates.

Answer

They allow for the identification of the rate-determining step.

Answer

They enable the accurate prediction of the reaction products.

Answer

They provide a precise measure of the activation energy of the reaction.

Question 38

In a reaction at constant temperature and pressure, which condition indicates spontaneity?

Accepted Answer

ΔH < 0 and ΔS > 0

Answer

ΔH > 0 and ΔS > 0

Answer

ΔH > 0 and ΔS < 0

Answer

ΔH < 0 and ΔS < 0

Question 39

Which of the following formulas accurately represents the change in enthalpy (ΔH) for a reaction?

Accepted Answer

ΔH = -Q + W

Answer

ΔH = Q - W

Answer

ΔH = Q + W

Answer

ΔH = -Q - W

Question 40

A system gains 50 J of heat and performs 20 J of work on its surroundings. What is the resulting change in the internal energy of the system?

Accepted Answer

30 J

Answer

50 J

Answer

70 J

Answer

-30 J

Question 41

Which of the following processes is exothermic?

Accepted Answer

Burning of gasoline

Answer

Melting of ice

Answer

Evaporation of water

Answer

Dissolving sugar in water

Question 42

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

Accepted Answer

Volume

Answer

Enthalpy change

Answer

Entropy change

Answer

Temperature

Question 43

Which of the following is a defining characteristic of an endothermic reaction?

Accepted Answer

Absorbs heat

Answer

Releases heat

Answer

Decreases temperature

Answer

Increases temperature

Question 44

Which unit is used to measure entropy?

Accepted Answer

Joules per Kelvin

Answer

Joules

Answer

Calories

Answer

Degrees Celsius

Question 45

How can thermochemistry be applied to solve environmental challenges? Provide specific examples to illustrate its practical applications.

Accepted Answer

Thermochemistry can be used to optimize combustion processes, reducing air pollution.

Accepted Answer

Thermochemistry helps assess the environmental impact of different energy sources.

Answer

Thermochemistry has no practical applications in environmental science and engineering.

Question 46

Which type of system can exchange both heat and matter with its surroundings?

Accepted Answer

Open system

Answer

Closed system

Answer

Isolated system

Question 47

State the first law of thermodynamics.

Accepted Answer

Energy cannot be created or destroyed, only transferred or transformed.

Answer

Entropy of a system always increases.

Answer

The heat capacity of a substance is constant.

Question 48

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

Accepted Answer

Volume of the reaction vessel

Answer

Temperature

Answer

Concentration of reactants

Question 49

What is the significance of activation energy in a chemical reaction?

Accepted Answer

It is the minimum energy required for a reaction to occur.

Answer

It is the maximum energy released in a reaction.

Answer

It is the average energy possessed by the reactants in a reaction.

Question 50

Describe the relationship between Gibbs free energy and the equilibrium constant.

Accepted Answer

Gibbs free energy is inversely proportional to the equilibrium constant.

Answer

Gibbs free energy is directly proportional to the equilibrium constant.

Answer

Gibbs free energy is not related to the equilibrium constant.

Question 51

Classify the following reaction: Combustion of methane (CH4).

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Athermal

Question 52

Define the enthalpy of vaporization.

Accepted Answer

The enthalpy change when one mole of liquid is converted to gas at its boiling point.

Answer

The enthalpy change when one mole of solid is converted to gas at its sublimation point.

Answer

The enthalpy change when one mole of gas is converted to liquid at its boiling point.

Question 53

Define heat capacity and explain its role in determining how different substances respond to heat addition.

Accepted Answer

Heat capacity measures the heat energy required to raise a substance's temperature by one degree Celsius.

Accepted Answer

Substances with higher heat capacities experience smaller temperature changes when heat is added.

Answer

Heat capacity has no significant effect on a substance's thermal behavior.

Answer

Heat capacity is a property found only in solids, while liquids and gases have negligible heat capacities.

Question 54

Which of the following statements accurately describes the First Law of Thermodynamics?

Accepted Answer

Energy within a closed system can be neither created nor destroyed.

Answer

Heat can flow from a cold object to a hot object spontaneously.

Answer

The total entropy of an isolated system never decreases.

Answer

Chemical reactions always release energy.

Question 55

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

Accepted Answer

Magnetic field strength

Answer

Temperature

Answer

Volume

Answer

Amount of substance

Question 56

What mathematical relationship exists between Gibbs free energy (G) and the equilibrium constant (K)?

Accepted Answer

ΔG = -RTlnK

Answer

ΔG = 0

Answer

ΔG = RTlnK

Answer

ΔG = -KlnRT

Question 57

According to the Third Law of Thermodynamics, what is the standard entropy change for a perfect crystal at absolute zero?

Accepted Answer

0 J/mol·K

Answer

1 J/mol·K

Answer

10 J/mol·K

Answer

100 J/mol·K

Question 58

How are heat capacity and specific heat related?

Accepted Answer

Heat capacity = Specific heat × Mass

Answer

Heat capacity = Specific heat ÷ Mass

Answer

Specific heat = Heat capacity × Mass

Answer

Specific heat = Heat capacity ÷ Mass

Question 59

Which of the following is an example of a closed thermodynamic system?

Accepted Answer

A beaker of water with a lid

Answer

A car engine running

Answer

A person breathing

Answer

A plant growing

Question 60

Consider a reaction with a substantial positive entropy change and a modest negative enthalpy change. Predict the spontaneity of this reaction at both low and high temperatures.

Accepted Answer

Spontaneous at low temperatures and non-spontaneous at elevated temperatures

Answer

Non-spontaneous at low temperatures and spontaneous at elevated temperatures

Answer

Spontaneous at both low and elevated temperatures

Question 61

Which of the following is the standard international (SI) unit of energy?

Accepted Answer

Joule (J)

Answer

Electronvolt (eV)

Answer

British thermal unit (Btu)

Answer

Calorie (cal)

Question 62

An exothermic reaction is characterized by:

Accepted Answer

Release of heat into the surroundings

Answer

Increase in Gibbs free energy

Answer

Decrease in entropy

Answer

Absorption of heat from the surroundings

Question 63

Enthalpy change (ΔH) of a reaction at constant pressure is defined as:

Accepted Answer

Heat absorbed or released by the system

Answer

Change in Gibbs free energy of the system

Answer

Change in entropy of the system

Answer

Change in internal energy of the system

Question 64

A substance with a negative Gibbs free energy change (ΔG) is:

Accepted Answer

Spontaneous at all temperatures

Answer

Non-spontaneous at high temperatures only

Answer

Spontaneous at low temperatures only

Answer

Non-spontaneous at all temperatures