Thermochemistry and Kinetics: Master Chemical Reactions and Energy

Question 1

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

Accepted Answer

Molecular shape of the reactants

Answer

Concentration of reactants

Answer

Temperature

Answer

Activation energy of the reaction

Question 2

Explain why the enthalpy change for vaporization is typically positive, considering both intermolecular forces and entropy changes during the process.

Accepted Answer

Positive enthalpy change is a result of breaking intermolecular forces and the increase in entropy during vaporization.

Answer

Positive enthalpy change is solely attributed to the increase in entropy during vaporization.

Answer

Positive enthalpy change occurs because the temperature of the system increases during vaporization.

Answer

Positive enthalpy change is a result of the volume of the system increasing during vaporization.

Question 3

Given a reaction with a positive Gibbs free energy change (ΔG > 0) at a particular temperature, what can be concluded about the spontaneity and equilibrium constant (K) of the reaction?

Accepted Answer

The reaction is nonspontaneous and K < 1.

Answer

The reaction is spontaneous and K > 1.

Answer

The reaction is spontaneous and K < 1.

Question 4

The decomposition of hydrogen peroxide (H2O2) follows first-order kinetics. If the concentration of H2O2 decreases by half every 10 minutes, determine the rate constant for this reaction.

Accepted Answer

0.0693 min^-1

Answer

0.10 min^-1

Answer

0.0347 min^-1

Answer

0.0173 min^-1

Question 5

According to collision theory, how does activation energy affect the probability of successful collisions between reactant molecules?

Accepted Answer

The probability of successful collisions decreases as activation energy increases.

Answer

Higher activation energy increases the likelihood of successful collisions.

Answer

Activation energy has no impact on the probability of successful collisions.

Question 6

How does increasing the surface area of a solid reactant influence the rate of a heterogeneous reaction? Explain the underlying reasons for this effect.

Accepted Answer

Increases the number of active sites, accelerating the reaction.

Answer

Decreases the activation energy, making the reaction proceed faster.

Answer

Decreases the concentration of the solid reactant, slowing down the reaction.

Answer

Has no effect on the reaction rate.

Question 7

Which of the following is the SI unit of energy?

Accepted Answer

Joule

Answer

Calorie

Answer

Electronvolt

Answer

British thermal unit

Question 8

The activation energy of a reaction is:

Accepted Answer

The minimum energy required for the reaction to occur

Answer

The maximum energy released during the reaction

Answer

The rate at which the reaction proceeds

Answer

The enthalpy change of the reaction

Question 9

The equilibrium constant of a reaction is:

Accepted Answer

The ratio of the concentrations of the products to the reactants at equilibrium

Answer

The ratio of the forward rate constant to the reverse rate constant

Answer

The value of the Gibbs free energy change at equilibrium

Answer

The temperature at which the forward and reverse reactions occur at the same rate

Question 10

The Gibbs free energy of a reaction is:

Accepted Answer

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

Answer

The enthalpy change of the reaction at constant pressure

Answer

The entropy change of the reaction at constant temperature

Answer

The equilibrium constant of the reaction

Question 11

The SI unit of enthalpy is:

Accepted Answer

Joule (J)

Answer

Calorie (cal)

Answer

Electronvolt (eV)

Answer

Kilocalorie (kcal)

Question 12

Which reaction has a negative change in entropy?

Accepted Answer

Crystallization of a solid

Answer

Melting of ice

Answer

Dissolving of sugar in water

Answer

Evaporation of a liquid

Question 13

Choose the rate law for a first-order reaction:

Accepted Answer

rate = k[A]

Answer

rate = k[A][B]

Answer

rate = k[A]^2

Answer

rate = k/t

Question 14

Define activation energy in a reaction:

Accepted Answer

Minimum energy required for a reaction to occur

Answer

Maximum energy released in a reaction

Answer

Difference in energy between reactants and products

Answer

Rate constant of a reaction

Question 15

Identify a characteristic of an exothermic reaction:

Accepted Answer

Releases heat

Answer

Absorbs heat

Answer

Increases in temperature

Answer

Decreases in temperature

Question 16

What does the equilibrium constant for a reaction signify?

Accepted Answer

Ratio of products to reactants at equilibrium

Answer

Ratio of reactants to products at equilibrium

Answer

Concentration of reactants and products at equilibrium

Answer

Rate constant of the forward reaction

Question 17

Which of these is a type of intermolecular force?

Accepted Answer

Hydrogen bonding

Answer

Ionic bonding

Answer

Covalent bonding

Answer

Metallic bonding

Question 18

Define the molar heat capacity of a substance:

Accepted Answer

Heat needed to raise the temperature of one mole by one Kelvin

Answer

Heat released when one mole undergoes a chemical reaction

Answer

Rate of temperature change over time

Answer

Specific heat multiplied by molar mass

Question 19

Which factor influences the activation energy of a reaction?

Accepted Answer

Catalyst nature

Answer

Temperature

Answer

Reactant concentration

Answer

Reactant surface area

Question 20

What is the rate law for a first-order reaction?

Accepted Answer

Rate = k[A]^1

Answer

Rate = k[A]^2

Answer

Rate = k[A]^0

Answer

Rate = k[A]^2[B]^1

Question 21

Entropy measures:

Accepted Answer

Disorder

Answer

Order

Answer

Energy

Answer

Temperature

Question 22

Which process is not spontaneous?

Accepted Answer

Corrosion of iron

Answer

Melting of ice at room temperature

Answer

Diffusion of gases

Answer

Mixing of hot and cold water

Question 23

The half-life of a first-order reaction is 10 minutes. What is its rate constant?

Accepted Answer

0.0693 min^-1

Answer

0.0115 min^-1

Answer

115 min^-1

Answer

693 min^-1

Question 24

Which substance is a catalyst?

Accepted Answer

Manganese dioxide

Answer

Sodium chloride

Answer

Hydrochloric acid

Answer

Sodium hydroxide

Question 25

The Arrhenius equation relates:

Accepted Answer

Rate constant to temperature

Answer

Activation energy to temperature

Answer

Half-life to temperature

Answer

Equilibrium constant to temperature

Question 26

Which of the following equations correctly represents the enthalpy change of a reaction?

Accepted Answer

ΔH = H(products) - H(reactants)

Answer

ΔH = H(reactants) + H(products)

Answer

ΔH = H(products) / H(reactants)

Answer

ΔH = H(reactants) / H(products)

Question 27

What are the factors that affect the entropy of a system?

Accepted Answer

Temperature, volume, and the number of particles

Answer

Temperature and volume

Answer

Temperature and the number of particles

Answer

Volume and the number of particles

Question 28

What is the mathematical relationship between free energy (G), enthalpy (H), and entropy (S)?

Accepted Answer

G = H - TS

Answer

G = H + TS

Answer

G = TS - H

Answer

G = H / TS

Question 29

What is the definition of a rate law?

Accepted Answer

An equation that expresses the rate of a reaction as a function of the concentrations of the reactants

Answer

An equation that expresses the rate of a reaction as a function of time

Answer

An equation that expresses the equilibrium constant of a reaction

Answer

An equation that expresses the activation energy of a reaction

Question 30

What is the meaning of the exponent in a rate law?

Accepted Answer

The order of the reaction with respect to that reactant

Answer

The stoichiometric coefficient of the reactant in the balanced chemical equation

Answer

The number of times the reactant appears in the rate-determining step

Answer

The activation energy of the reaction

Question 31

What is activation energy?

Accepted Answer

The minimum amount of energy that reactants must possess in order to react

Answer

The maximum amount of energy that can be released by a reaction

Answer

The difference in energy between the reactants and the products

Answer

The energy required to break all bonds in the reactants

Question 32

Which of the following reactions is an example of a spontaneous reaction?

Accepted Answer

The combustion of gasoline

Answer

The electrolysis of water

Answer

The decomposition of water into hydrogen and oxygen

Answer

The freezing of water

Question 33

What is the equilibrium constant for a reaction?

Accepted Answer

The ratio of the concentrations of the products to the concentrations of the reactants at equilibrium

Answer

The ratio of the rate constants of the forward and reverse reactions

Answer

The free energy change of the reaction

Answer

The activation energy of the reaction

Question 34

Which quantity measures the level of disorder or randomness within a system?

Accepted Answer

Entropy

Answer

Enthalpy

Answer

Free energy

Answer

Activation energy

Question 35

The rate law for a reaction that proceeds via a first-order mechanism can be expressed as:

Accepted Answer

Rate = k[A]

Answer

Rate = k[A]^2

Answer

Rate = k[A][B]

Answer

Rate = k[A]^0.5

Question 36

The activation energy of a reaction represents:

Accepted Answer

The minimum energy required for a reaction to occur

Answer

The maximum energy released by a reaction

Answer

The difference in energy between reactants and products

Answer

The slope of the Arrhenius plot

Question 37

The half-life of a radioactive isotope is:

Accepted Answer

The time required for half of the isotope to decay

Answer

The time needed for all of the isotope to decay

Answer

The decay rate of the isotope

Answer

The concentration of the isotope

Question 38

How does a catalyst influence the activation energy of a reaction? Explain the consequences of this effect on the reaction rate and equilibrium position.

Accepted Answer

A catalyst lowers the activation energy, enabling the reaction to occur more rapidly and shifting the equilibrium towards products.

Answer

A catalyst increases the activation energy, slowing down the reaction and shifting the equilibrium towards reactants.

Answer

A catalyst has no impact on activation energy but accelerates the reaction by providing additional reactants.

Answer

A catalyst alters the equilibrium position without affecting the reaction rate.

Question 39

A reaction associated with a negative change in enthalpy is:

Accepted Answer

Exothermic

Answer

Endothermic

Answer

Isothermal

Answer

Adiabatic

Question 40

A rate law for a reaction is an equation that:

Accepted Answer

Relates the reaction rate to reactant concentrations

Answer

Graphically depicts the reaction rate over time

Answer

Lists the steps in the reaction mechanism

Answer

Represents the equilibrium constant

Question 41

Which of the following is a catalyst?

Accepted Answer

A substance that accelerates a reaction without being consumed

Answer

A substance that slows down a reaction without being consumed

Answer

A substance consumed during the reaction

Answer

A substance produced during the reaction

Question 42

The half-life of a reaction is the:

Accepted Answer

Time taken for reactant concentration to halve

Answer

Time taken for product concentration to double

Answer

Time taken to reach equilibrium

Answer

Time taken for the reaction to complete

Question 43

The standard state for enthalpy changes is defined as:

Accepted Answer

1 atm and 298 K

Answer

1 atm and 0 K

Answer

1 atm and 100 °C

Answer

1 atm and 373 K

Question 44

The activation energy of a reaction represents:

Accepted Answer

The minimum energy required for the reaction to occur

Answer

The maximum energy released by the reaction

Answer

The difference in energy between the reactants and products

Answer

The rate of the reaction

Question 45

The unit of entropy is:

Accepted Answer

J/mol K

Answer

J/mol

Answer

mol/L

Answer

L/mol

Question 46

The free energy change of a reaction represents:

Accepted Answer

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

Answer

The minimum amount of work that must be done to start the reaction

Answer

The difference in energy between the reactants and products

Answer

The rate of the reaction

Question 47

A reaction with a negative free energy change is:

Accepted Answer

Spontaneous

Answer

Non-spontaneous

Answer

Exothermic

Answer

Endothermic

Question 48

The rate law for a reaction expresses:

Accepted Answer

The relationship between the rate of the reaction and the concentrations of the reactants

Answer

The value of the rate constant

Answer

The order of the reaction

Answer

The activation energy of the reaction

Question 49

A first-order reaction is characterized by:

Accepted Answer

A rate that is directly proportional to the concentration of only one reactant

Answer

A rate that is directly proportional to the concentrations of two reactants

Answer

A rate that is independent of the concentrations of the reactants

Answer

A rate that is inversely proportional to the concentrations of the reactants

Question 50

The half-life of a reaction is:

Accepted Answer

The time it takes for the concentration of the reactants to decrease by half

Answer

The time it takes for the concentration of the products to increase by half

Answer

The time it takes for the rate of the reaction to decrease by half

Answer

The time it takes for the equilibrium constant to reach half of its maximum value

Question 51

The standard unit of enthalpy change is:

Accepted Answer

kJ/mol

Answer

kcal/mol

Answer

J/mol

Answer

kWh/mol

Question 52

Burning of fuel is an example of a(n):

Accepted Answer

Exothermic process

Answer

Endothermic process

Answer

Reversible process

Answer

Irreversible process

Question 53

The activation energy of a reaction is:

Accepted Answer

The minimum energy required for the reaction to occur

Answer

The maximum energy released during the reaction

Answer

The difference in enthalpy between the reactants and products

Answer

The rate constant of the reaction

Question 54

The equilibrium constant for a reaction represents:

Accepted Answer

The ratio of the concentrations of the products to the reactants at equilibrium

Answer

The rate constant for the forward reaction

Answer

The activation energy for the reverse reaction

Answer

The change in enthalpy for the reaction

Question 55

A battery discharging is an example of a(n):

Accepted Answer

Spontaneous process

Answer

Non-spontaneous process

Answer

Reversible process

Answer

Irreversible process

Question 56

Activation energy (Ea) is:

Accepted Answer

The minimum energy required for a reaction to occur

Answer

The difference in energy between reactants and products

Answer

The energy of the transition state

Answer

The maximum energy released during a reaction

Question 57

Which of the following processes is exothermic?

Accepted Answer

Combustion of propane

Answer

Melting of ice

Answer

Evaporation of water

Answer

Dissolution of sodium chloride in water

Question 58

The rate law for a reaction expresses the:

Accepted Answer

Relationship between the rate of reaction and the concentrations of reactants

Answer

Equilibrium constant for the reaction

Answer

Activation energy for the reaction

Answer

Products of the reaction

Question 59

A spontaneous process is one that:

Accepted Answer

Occurs without external input of energy

Answer

Releases heat to the surroundings

Answer

Requires a catalyst to occur

Answer

Is always exothermic

Question 60

Gibbs free energy (G) is used to:

Accepted Answer

Predict the spontaneity of a reaction

Answer

Calculate the equilibrium constant for a reaction

Answer

Determine the rate of a reaction

Answer

Identify the products of a reaction

Question 61

Which of the following reactions has a negative change in entropy?

Accepted Answer

Formation of a crystal

Answer

Melting of ice

Answer

Evaporation of water

Answer

Dissolution of a solid in a liquid

Question 62

The reaction: CH₄ + 2O₂ → CO₂ + 2H₂O is:

Accepted Answer

Exothermic and spontaneous

Answer

Endothermic and spontaneous

Answer

Exothermic and non-spontaneous

Answer

Endothermic and non-spontaneous

Question 63

Which thermodynamic quantity determines whether a chemical reaction is spontaneous?

Accepted Answer

Gibbs free energy change (ΔG)

Answer

Enthalpy change (ΔH)

Answer

Entropy change (ΔS)

Question 64

In a reaction mechanism, which step is the slowest and determines the overall reaction rate?

Accepted Answer

The step with the slowest rate

Answer

The first step of the reaction

Answer

The step with the lowest activation energy