Energetics: Master Energy Changes in Chemical Reactions

Question 1

In thermodynamics, which of these is NOT a state function?

Accepted Answer

Work

Answer

Internal energy

Answer

Enthalpy

Answer

Entropy

Question 2

Define entropy and explain its relationship to the disorder or randomness of a system. Provide specific examples to illustrate this connection.

Accepted Answer

Entropy increases as the disorder or randomness of a system increases. For instance, when ice melts, the water molecules become less ordered, and entropy increases.

Answer

Entropy is a measure of the amount of energy in a system.

Answer

Entropy is a measure of the amount of heat in a system.

Answer

Entropy decreases as the disorder or randomness of a system increases.

Question 3

How does the microscopic disorder of a system affect its entropy? Give a real-world example to show this relationship and its implications for chemical reactions.

Accepted Answer

A system with more disorder has higher entropy because it has more possible arrangements of its particles.

Answer

A system with more disorder has lower entropy because it has fewer possible arrangements of its particles.

Answer

The microscopic disorder of a system does not affect its entropy.

Question 4

Explain the relationship between temperature and entropy. Use specific examples to support your answer.

Accepted Answer

As temperature increases, entropy increases because particles become more disordered and have more possible arrangements.

Answer

As temperature decreases, entropy decreases because particles become more ordered.

Answer

Temperature has no effect on entropy.

Answer

As temperature increases, entropy decreases because particles lose energy.

Question 5

Why does the entropy of an isolated system increase over time, according to the second law of thermodynamics?

Accepted Answer

Matter tends to disperse and become more disordered, increasing entropy.

Answer

The universe gains energy, leading to increased entropy.

Answer

The second law of thermodynamics is related to the laws of motion.

Answer

The universe's expansion increases entropy.

Question 6

In a chemical reaction, the number of gaseous moles increases from 2 to 4. How does this change contribute to the overall entropy change of the system?

Accepted Answer

Entropy increases due to an increase in gaseous moles.

Answer

Entropy decreases due to a decrease in gaseous moles.

Answer

Entropy remains unchanged because the total number of moles is constant.

Question 7

Which of the following factors does NOT affect entropy?

Accepted Answer

Volume

Answer

Temperature

Answer

Number of molecules

Answer

Molecular complexity

Question 8

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

Accepted Answer

Enthalpy change minus temperature times entropy change

Answer

Enthalpy change plus temperature times entropy change

Answer

Entropy change minus enthalpy change

Answer

Temperature change multiplied by entropy change

Question 9

The equilibrium constant for a reaction is:

Accepted Answer

Equal to the rate of the forward reaction divided by the rate of the reverse reaction

Answer

A measure of the extent of the reaction

Answer

Independent of temperature

Answer

Always greater than 1

Question 10

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

Accepted Answer

Zero

Answer

Positive

Answer

Negative

Answer

Dependent on pressure

Question 11

The entropy of a system is a measure of its:

Accepted Answer

Disorder

Answer

Energy

Answer

Temperature

Answer

Pressure

Question 12

Which of the following is NOT a state function?

Accepted Answer

Volume

Answer

Enthalpy

Answer

Entropy

Answer

Internal energy

Question 13

A reaction with a negative free energy change is:

Accepted Answer

Spontaneous

Answer

Non-spontaneous

Answer

At equilibrium

Question 14

Which of the following processes is exothermic?

Accepted Answer

Combustion of gasoline

Answer

Melting of ice

Answer

Condensation of water vapor

Answer

Sublimation of dry ice

Question 15

Which of the following is a unit of enthalpy?

Accepted Answer

Joule

Answer

Kelvin

Answer

Entropy unit

Answer

Mole

Question 16

The spontaneity of a reaction can be predicted by considering:

Accepted Answer

Both enthalpy change and entropy change

Answer

Enthalpy change only

Answer

Entropy change only

Answer

Free energy change only

Question 17

The standard enthalpy of formation of a substance is:

Accepted Answer

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

Answer

The enthalpy change when the substance is burned in excess oxygen

Answer

The enthalpy change when the substance is dissolved in water

Answer

The enthalpy change when the substance reacts with another substance

Question 18

Define the standard enthalpy change of formation.

Accepted Answer

Enthalpy change when one mole of a substance is formed from its element constituents in their standard states

Answer

Enthalpy change when one gram of a substance is formed from its element constituents in their standard states

Answer

Enthalpy change when one mole of a substance reacts with oxygen

Answer

Enthalpy change when one gram of a substance reacts with hydrogen

Question 19

Identify the criterion for a spontaneous reaction.

Accepted Answer

ΔG < 0

Answer

ΔG > 0

Answer

ΔG = 0

Answer

ΔG = ∞

Question 20

Which factor does not influence the equilibrium constant of a reaction?

Accepted Answer

Presence of a catalyst

Answer

Temperature

Answer

Pressure

Answer

Concentration of reactants and products

Question 21

An exothermic reaction is characterized by:

Accepted Answer

Releasing heat

Answer

Absorbing heat

Answer

No heat change

Answer

Decrease in entropy

Question 22

State the Second Law of Thermodynamics.

Accepted Answer

The entropy of the universe always increases

Answer

The entropy of the universe always decreases

Answer

The entropy of the universe remains constant

Answer

The entropy of the universe can increase or decrease

Question 23

Define the enthalpy change of a reaction.

Accepted Answer

Heat released by the system minus work done by the system

Answer

Heat absorbed by the system plus work done by the system

Answer

Work done by the system minus heat released by the system

Answer

Work done by the system plus heat absorbed by the system

Question 24

Which type of reaction releases heat?

Accepted Answer

Exothermic reaction

Answer

Endothermic reaction

Answer

Neither exothermic nor endothermic

Answer

Both exothermic and endothermic

Question 25

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

Accepted Answer

0 kJ mol^-1

Answer

100 kJ mol^-1

Answer

The enthalpy change when 1 mol of the element is formed from its constituent atoms

Answer

Cannot be determined

Question 26

Predict the spontaneity of a reaction with ΔG < 0.

Accepted Answer

Spontaneous at all temperatures

Answer

Non-spontaneous at all temperatures

Answer

Spontaneous at high temperatures

Answer

Non-spontaneous at low temperatures

Question 27

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

Accepted Answer

It is the minimum energy required to start the reaction

Answer

It is the maximum energy released during the reaction

Answer

It is the difference in energy between reactants and products

Answer

It has no relation to the rate of reaction

Question 28

What best describes a catalyst?

Accepted Answer

A substance that speeds up a reaction without being consumed

Answer

A substance that slows down a reaction without being consumed

Answer

A substance that is consumed in a reaction

Answer

A substance that does not participate in a reaction

Question 29

Distinguish between endergonic and exergonic reactions.

Accepted Answer

Endergonic reactions have positive ΔG and exergonic reactions have negative ΔG

Answer

Endergonic reactions have negative ΔG and exergonic reactions have positive ΔG

Answer

Endergonic reactions involve energy release and exergonic reactions involve energy absorption

Answer

Endergonic and exergonic reactions are the same thing

Question 30

Which of the following is a thermodynamic property?

Accepted Answer

Entropy

Answer

Mass

Answer

Volume

Answer

Density

Question 31

The heat absorbed by a system at constant pressure is equal to the change in:

Accepted Answer

Enthalpy

Answer

Entropy

Answer

Gibbs free energy

Answer

Internal energy

Question 32

Which of the following reactions is exothermic?

Accepted Answer

Respiration in humans

Answer

Dissolution of sodium chloride in water

Answer

Condensation of water vapor

Answer

Melting of ice

Question 33

Entropy is a measure of:

Accepted Answer

Disorder or randomness of a system

Answer

Total energy of a system

Answer

Heat capacity of a system

Answer

Rate of a reaction

Question 34

Which factor(s) determine the spontaneity of a reaction?

Accepted Answer

(a) and (b)

Answer

Enthalpy change (ΔH)

Answer

Entropy change (ΔS)

Answer

Gibbs free energy change (ΔG)

Question 35

The standard Gibbs free energy change (ΔG°) for a reaction represents:

Accepted Answer

The change in Gibbs free energy when all reactants and products are in their standard states

Answer

The maximum amount of work that can be obtained from the reaction

Answer

The change in entropy of the surroundings

Answer

A positive value for spontaneous reactions

Question 36

Which of the following reactions is NOT spontaneous under standard conditions?

Accepted Answer

Electrolysis of water (2H2O → 2H2 + O2)

Answer

Haber process (N2 + 3H2 → 2NH3)

Answer

Combustion of methane (CH4 + 2O2 → CO2 + 2H2O)

Answer

Dissolution of sodium chloride in water (NaCl(s) → Na+(aq) + Cl-(aq))

Question 37

The equilibrium constant (Kc) for a reaction is:

Accepted Answer

The ratio of the concentrations of products to reactants at equilibrium

Answer

Always greater than 1

Answer

Dependent on the initial concentrations of reactants and products

Answer

A measure of the rate of the reaction

Question 38

In an exothermic reaction, there is a:

Accepted Answer

Release of heat

Answer

Absorption of heat

Answer

Decrease in entropy

Answer

Decrease in enthalpy

Question 39

The standard enthalpy change of formation of a substance is the enthalpy change when:

Accepted Answer

1 mole of the substance is formed from its elements in their standard states

Answer

1 gram of the substance is formed from its elements in their standard states

Answer

1 mole of the substance is formed from its ions in their standard states

Answer

1 gram of the substance is formed from its ions in their standard states

Question 40

The enthalpy change of a reaction is:

Accepted Answer

The heat exchanged between the system and surroundings

Answer

The change in internal energy of the system

Answer

The work done by the system

Answer

The change in entropy of the system

Question 41

Which of the following is a system that can exchange both heat and work with the surroundings?

Accepted Answer

Open system

Answer

Closed system

Answer

Isolated system

Answer

Adiabatic system

Question 42

According to the second law of thermodynamics, the entropy of an isolated system:

Accepted Answer

Always increases

Answer

Always decreases

Answer

Always remains constant

Answer

May increase or decrease depending on the specific conditions

Question 43

The standard enthalpy of formation of CO2(g) is -393.5 kJ/mol. Calculate the enthalpy change when 2 moles of CO2(g) are formed:

Accepted Answer

-787 kJ

Answer

-393.5 kJ

Answer

-196.75 kJ

Answer

196.75 kJ

Question 44

Identify the type of thermodynamic system in which no mass or energy can enter or leave:

Accepted Answer

A sealed flask containing a gas

Answer

An open container filled with liquid

Answer

A car engine in operation

Answer

A beaker of water placed in a room

Question 45

According to the Third Law of Thermodynamics, the entropy of a pure crystalline substance approaches what value at absolute zero?

Accepted Answer

Zero

Answer

Positive infinity

Answer

Negative infinity

Answer

A specific non-zero value

Question 46

Which factor has no influence on the spontaneity of a reaction?

Accepted Answer

Volume (V)

Answer

Enthalpy change (ΔH)

Answer

Entropy change (ΔS)

Answer

Temperature (T)

Question 47

Which experimental technique is commonly used to measure the enthalpy change of a reaction?

Accepted Answer

Calorimetry

Answer

Spectroscopy

Answer

Titration

Answer

Electrochemistry

Question 48

The heat capacity of a substance represents its:

Accepted Answer

Ability to absorb heat

Answer

Ability to release heat

Answer

Temperature

Answer

Enthalpy

Question 49

Define the change in enthalpy of a reaction.

Accepted Answer

ΔH = Hproducts - Hreactants

Answer

ΔH = Hreactants - Hproducts

Answer

ΔH = - (Hproducts - Hreactants)

Answer

ΔH = (Hreactants - Hproducts) / 2

Question 50

In an exothermic reaction, heat is transferred to the surroundings, resulting in a:

Accepted Answer

Release of heat

Answer

Absorption of heat

Answer

No change in heat

Answer

Release of heat only at high temperatures

Question 51

What determines the spontaneity of a reaction?

Accepted Answer

Free energy

Answer

Enthalpy alone

Answer

Entropy alone

Answer

Temperature alone

Question 52

Define the standard enthalpy of formation for an element in its standard state.

Accepted Answer

0 kJ/mol

Answer

Always positive

Answer

Always negative

Answer

Dependent on temperature

Question 53

Which characteristic is associated with spontaneous reactions?

Accepted Answer

Negative ΔG

Answer

Positive ΔH

Answer

Negative ΔS

Answer

Positive ΔE

Question 54

Identify the endothermic reaction among the following:

Accepted Answer

Sodium chloride dissolving in water

Answer

Methane combustion

Answer

Acid-base neutralization

Answer

Water vapor condensation

Question 55

What is the significance of the equilibrium constant in a reaction?

Accepted Answer

It indicates the relative amounts of reactants and products at equilibrium

Answer

It is always greater than 1

Answer

It is always less than 1

Answer

It is independent of temperature

Question 56

Design an experiment using calorimetry to determine the standard enthalpy of formation of a compound. Explain the significance of standard states in thermochemical calculations.

Accepted Answer

Correct: This experiment outlines a valid calorimetry experiment and explains the importance of standard states.

Answer

Incorrect: This experiment uses the enthalpy of combustion, not formation.

Answer

Incorrect: This experiment does not account for the temperature change.

Answer

Incorrect: This experiment does not consider the reactants and products involved.

Question 57

Design an experiment to determine the heat capacity of a substance.

Accepted Answer

Measure the temperature change of the substance when a known amount of heat is added.

Answer

Measure the mass of the substance and its specific heat capacity.

Answer

Calculate the heat capacity using theoretical models and assumptions.

Answer

Measure the rate of heat transfer between the substance and a heat sink.

Question 58

A chemical reaction has a positive entropy change. How will this affect the spontaneity of the reaction as the temperature increases?

Accepted Answer

The reaction will become more spontaneous.

Answer

The reaction will become less spontaneous.

Answer

The spontaneity of the reaction will not be affected by temperature.

Answer

The reaction will become nonspontaneous.

Question 59

Explain the distinction between exergonic and endergonic reactions based on their free energy change and spontaneity.

Accepted Answer

Exergonic reactions have a negative free energy change and are spontaneous, while endergonic reactions have a positive free energy change and are nonspontaneous.

Answer

Exergonic reactions have a positive free energy change and are nonspontaneous.

Answer

Endergonic reactions have a negative free energy change and are spontaneous.

Answer

Free energy change is irrelevant to reaction spontaneity.

Question 60

What is the main purpose of using standard entropy values in chemical calculations?

Accepted Answer

To calculate the total entropy change of a reaction

Answer

To determine the absolute entropy of a substance

Answer

To predict the spontaneity of a reaction

Answer

To determine the temperature and pressure dependence of entropy

Question 61

To determine the standard enthalpy of formation of calcium oxide (CaO) using calorimetry, which experimental setup is most appropriate?

Accepted Answer

Burn calcium metal in a calorimeter containing a known amount of oxygen.

Answer

React calcium oxide (CaO) with water in a calorimeter.

Answer

Add calcium carbonate (CaCO3) to a strong acid in a calorimeter.

Answer

Heat calcium metal in a sealed container and measure the pressure change.

Question 62

Under non-standard conditions, a positive ΔG value indicates that the reaction will:

Accepted Answer

Proceed spontaneously in the reverse direction

Answer

Proceed spontaneously in the forward direction

Answer

Reach chemical equilibrium

Question 63

Which statement accurately describes the relationship between enthalpy and entropy changes in chemical reactions, and their combined effect on spontaneity?

Accepted Answer

A negative Gibbs free energy change indicates spontaneity and a preference for the forward reaction.

Answer

When both enthalpy and entropy changes are negative, the reaction is always spontaneous and exothermic.

Answer

A reaction with a positive enthalpy change and a negative entropy change is non-spontaneous at all temperatures.

Answer

A large equilibrium constant signifies that the reverse reaction will dominate.

Question 64

Which of the following statements about enthalpy is true?

Accepted Answer

Enthalpy is a state function, meaning it depends only on the current state of the system, not on the path taken to reach that state.

Answer

Enthalpy is only defined for closed systems, meaning that no mass or energy can enter or leave the system.

Answer

Enthalpy is the internal energy of a system plus its pressure-volume work.

Answer

Enthalpy is a path function, meaning it depends on the path taken to reach a particular state.