Chemical Reaction Rates: Master Kinetics for Chemistry Success

Question 1

Describe the key differences between homogeneous and heterogeneous reaction mechanisms, and provide an example of each.

Accepted Answer

Homogeneous reactions occur in a single phase, while heterogeneous reactions occur at the interface of two phases.

Answer

Unimolecular reactions involve a single molecule, while bimolecular reactions involve two molecules.

Answer

Endothermic reactions absorb heat, while exothermic reactions release heat.

Answer

Spontaneous reactions occur without an input of energy, while non-spontaneous reactions require an input of energy.

Question 2

In a chemical reaction involving gaseous reactants, which method can be used to determine the reaction order?

Accepted Answer

Measuring partial pressures of reactants and products over time

Answer

Using a catalyst to speed up the reaction

Answer

Measuring the activation energy of the reaction

Question 3

A reaction's rate law is an equation that describes the relationship between the:

Accepted Answer

Reaction rate and concentrations of the reactants

Answer

Activation energy and the temperature

Answer

Equilibrium constant and the concentrations of reactants and products

Answer

Reaction rate and the surface area of the reactants

Question 4

Select the correct definition of a catalyst:

Accepted Answer

A substance that increases reaction rate without being consumed

Answer

A substance that decreases reaction rate

Answer

A reactant in the reaction

Answer

A product of the reaction

Question 5

The Arrhenius equation expresses the relationship between:

Accepted Answer

Rate constant, activation energy, and temperature

Answer

Equilibrium constant and the concentrations of reactants and products

Answer

Reaction rate and the concentrations of the reactants

Answer

Free energy change and equilibrium constant

Question 6

In the rate law 'rate = k[A][B]^2', what is the reaction order with respect to [B]?

Accepted Answer

2

Answer

0

Answer

1

Answer

3

Question 7

In a zero-order reaction, which statement is true?

Accepted Answer

The reaction rate is unaffected by reactant concentrations

Answer

The reaction rate is directly proportional to reactant concentrations

Answer

The reaction rate is inversely proportional to reactant concentrations

Answer

The reaction rate is second-order

Question 8

Evaluate the statement: 'Chemical kinetics is solely concerned with determining the rate of a reaction.' Justify your response.

Accepted Answer

The statement is inaccurate because kinetics also investigates reaction mechanisms.

Answer

The statement is accurate because kinetics focuses solely on reaction rates.

Answer

The statement is inaccurate because kinetics encompasses both reaction rates and equilibrium.

Question 9

Which of the following factors does NOT influence the rate of a chemical reaction?

Accepted Answer

Nature of the solvent

Answer

Concentration of reactants

Answer

Temperature

Answer

Surface area of reactants (for heterogeneous reactions)

Question 10

Which factors primarily influence the rate of a chemical reaction?

Accepted Answer

Temperature

Accepted Answer

Concentration of reactants

Accepted Answer

Presence of a catalyst

Answer

Volume of the reaction container

Question 11

The reaction rate of a chemical reaction is directly proportional to the concentration of the reactants raised to the power of their:

Accepted Answer

Reaction orders

Answer

Activation energy

Answer

Equilibrium constant

Question 12

The activation energy of a reaction is the minimum amount of energy that must be supplied to:

Accepted Answer

Reactants to transform into products

Answer

Products to transform into reactants

Answer

Reactions to reach equilibrium

Answer

Catalysts to become active

Question 13

The mathematical expression that represents the relationship between the reaction rate and the concentration of reactants is known as the:

Accepted Answer

Rate law

Answer

Activation energy

Answer

Equilibrium constant

Question 14

The half-life of a reaction is best described as:

Accepted Answer

The amount of time required for the concentration of the reactant to decrease by half

Answer

The time it takes for the reaction to reach completion

Answer

The time it takes for the catalyst to become active

Question 15

The Arrhenius equation is used to describe:

Accepted Answer

The temperature dependence of reaction rates

Answer

The concentration dependence of reaction rates

Answer

The effect of catalysts on reaction rates

Answer

The relationship between equilibrium constants and reaction rates

Question 16

Reactions with high activation energies are typically:

Accepted Answer

Slower at lower temperatures

Answer

Independent of temperature

Answer

Faster at lower temperatures

Answer

Catalyzed by most enzymes

Question 17

The derived unit expressing the rate of a chemical reaction is:

Accepted Answer

M/s

Answer

J/s

Answer

K

Answer

mol/L

Question 18

The rate constant of a reaction is defined as:

Accepted Answer

A constant that describes the rate of a reaction under specific conditions

Answer

A parameter that can be adjusted to control the reaction rate

Answer

A variable that depends on the concentration of the reactants

Question 19

Which of the following factors does NOT affect the rate of a chemical reaction?

Accepted Answer

Concentration of the catalyst

Answer

Concentration of the reactants

Answer

Surface area of the reactants

Answer

Temperature

Question 20

The rate law for the reaction A + B → C is rate = k[A][B]^2. What is the overall order of the reaction?

Accepted Answer

Third order

Answer

Fourth order

Answer

Second order

Answer

First order

Question 21

Which of the following is a catalyst used in the Haber process for ammonia synthesis?

Accepted Answer

Iron oxide

Answer

Sodium chloride

Answer

Calcium carbonate

Answer

Potassium hydroxide

Question 22

The activation energy of a reaction corresponds to the:

Accepted Answer

Minimum energy required to initiate a chemical reaction

Answer

Difference in energy between products and reactants

Answer

Energy absorbed by the system during a reaction

Answer

Energy released as heat during a reaction

Question 23

Which of the following graphical representations can be used to determine the order of a reaction?

Accepted Answer

Logarithm of concentration versus time

Answer

Concentration versus time

Answer

Inverse of concentration versus time

Answer

Logarithm of rate versus time

Question 24

A reaction proceeds with an activation energy of 80 kJ/mol. Assuming a temperature of 298 K, what is the numerical value of the rate constant?

Accepted Answer

2.6 x 10^-9 s^-1

Answer

7.4 x 10^-8 s^-1

Answer

1.4 x 10^-10 s^-1

Question 25

Which of the following is a central postulate of transition state theory?

Accepted Answer

The activated complex, a transient intermediate, is in equilibrium with the reactants

Answer

The activated complex is a stable intermediate

Answer

The rate-determining step is always the initial step in the reaction

Question 26

Which of the following factors can influence the rate of a reaction?

Accepted Answer

Temperature, concentration, and presence of a catalyst

Answer

Presence of a catalyst only

Answer

Concentration only

Answer

Temperature only

Question 27

The activation energy of a reaction is:

Accepted Answer

The minimum amount of energy required for a reaction to proceed

Answer

The maximum amount of energy released during a reaction

Answer

The difference in energy between the reactants and the transition state

Question 28

The relationship between the rate constant and the activation energy of a reaction is that:

Accepted Answer

The rate constant decreases as the activation energy increases

Answer

The rate constant does not depend on the activation energy

Answer

The rate constant is directly proportional to the activation energy

Question 29

Which of the following represents a heterogeneous reaction?

Accepted Answer

Reaction between a solid and a gas

Answer

Reaction between two liquids

Answer

Reaction between two gases

Question 30

What is the order of a reaction with respect to a reactant?

Accepted Answer

The exponent to which the concentration of the reactant is raised in the rate law

Answer

The number of moles of the reactant present

Answer

The stoichiometric coefficient of the reactant in the balanced chemical equation

Question 31

What is the half-life of a reaction?

Accepted Answer

The time it takes for half of the reactants to be consumed

Answer

The time it takes for the reaction to reach completion

Answer

The time it takes for the concentration of the reactants to double

Question 32

Which of the following is a bimolecular reaction?

Accepted Answer

2NO + O2 → 2NO2

Answer

NO2 + O2 → NO3

Answer

2NO2 → 2NO + O2

Answer

NO + O2 → NO2

Question 33

The rate law for a reaction is: rate = k[A][B]^2. What is the order of the reaction with respect to A?

Accepted Answer

1

Answer

3

Answer

2

Answer

0

Question 34

A reaction has an activation energy of 100 kJ/mol. What is the effect of increasing the temperature from 25 °C to 50 °C on the rate constant?

Accepted Answer

Increases by a factor of about 4.

Answer

Increases by a factor of about 2.

Answer

Decreases by a factor of about 4.

Answer

Decreases by a factor of about 2.

Question 35

Which of the following is a catalyst?

Accepted Answer

Enzyme

Answer

Reactant

Answer

Product

Answer

Inhibitor

Question 36

The half-life of a first-order reaction is 10 minutes. What percentage of the reactant remains after 30 minutes?

Accepted Answer

12.5%

Answer

75%

Answer

25%

Answer

50%

Question 37

Which of the following graphs represents a zero-order reaction?

Accepted Answer

(Concentration of reactant) vs. Time = linear decrease

Answer

(Concentration of reactant) vs. Time = exponential decrease

Answer

(Concentration of reactant)^2 vs. Time = linear decrease

Question 38

A reaction proceeds via a two-step mechanism. The first step is fast and reversible, while the second step is slow and irreversible. Which step is the rate-determining step?

Accepted Answer

Second step

Answer

Neither step

Answer

Both steps

Answer

First step

Question 39

Which of the following statements about transition state theory is incorrect?

Accepted Answer

The transition state is a stable intermediate.

Answer

The transition state is the highest energy point along the reaction pathway.

Answer

The transition state has higher energy than the reactants and products.

Answer

The transition state is formed when the reactants overcome the activation energy barrier.

Question 40

Which of the following factors does NOT affect the rate of a chemical reaction?

Accepted Answer

Temperature

Answer

Concentration of reactants

Answer

Surface area of reactants

Question 41

The rate law for a reaction is: rate = k[A][B]. What is the order of the reaction with respect to reactant B?

Accepted Answer

1

Answer

-1

Answer

0

Answer

2

Question 42

Which of the following is NOT a unit for the rate constant in a second-order reaction?

Accepted Answer

M

Answer

M/s

Answer

1/M-s

Answer

1/M

Question 43

What is the relationship between activation energy and the rate of a chemical reaction?

Accepted Answer

A higher activation energy leads to a slower reaction rate

Answer

Activation energy has no effect on reaction rate

Answer

A higher activation energy leads to a faster reaction rate

Question 44

Which of the following is 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

Question 45

What is the effect of a temperature increase on the rate of a reaction?

Accepted Answer

The rate will increase

Answer

The rate will first increase and then decrease

Answer

The rate will not change

Answer

The rate will decrease

Question 46

Which of the following is a pseudo-first-order reaction?

Accepted Answer

A reaction in which one reactant is in large excess

Answer

A reaction in which the rate is independent of reactant concentration

Answer

A reaction in which both reactants are in equal concentrations

Question 47

What is the half-life of a reaction?

Accepted Answer

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

Answer

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

Answer

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

Question 48

What is the difference between a homogeneous and a heterogeneous reaction?

Accepted Answer

In a homogeneous reaction, reactants and products are in the same phase, while in a heterogeneous reaction, they are in different phases

Answer

In a heterogeneous reaction, reactants and products are in the same phase, while in a homogeneous reaction, they are in different phases

Question 49

The rate constant for a reaction is 0.05 s⁻¹ at 25°C. What is the rate of the reaction if the initial concentration of the reactant is 0.2 M?

Accepted Answer

0.01 M/s

Answer

0.1 M/s

Answer

0.025 M/s

Answer

0.05 M/s

Question 50

A reaction has a rate constant of 1.2 x 10⁻⁴ s⁻¹ at 25°C and an activation energy of 50 kJ/mol. What is the rate constant at 50°C?

Accepted Answer

1.2 x 10⁻³ s⁻¹

Answer

6.0 x 10⁻⁴ s⁻¹

Answer

2.4 x 10⁻⁴ s⁻¹

Question 51

Which of the following factors can affect the rate of a chemical reaction?

Accepted Answer

All of the above

Answer

Temperature

Answer

Concentration of reactants

Answer

Presence of a catalyst

Question 52

The decomposition of N₂O₅ is a first-order reaction. If the initial concentration of N₂O₅ is 0.1 M and the rate constant is 0.05 s⁻¹, what is the concentration of N₂O₅ after 10 seconds?

Accepted Answer

0.0067 M

Answer

0.0033 M

Answer

0.01 M

Answer

0.05 M

Question 53

Which of the following statements about catalysts is TRUE?

Accepted Answer

Catalysts lower the activation energy of a reaction.

Answer

Catalysts are consumed in the reaction.

Answer

Catalysts increase the enthalpy change of a reaction.

Question 54

The rate law for the reaction 2NO(g) + O₂(g) → 2NO₂(g) is rate = k[NO]²[O₂]. What is the overall order of the reaction?

Accepted Answer

Third order

Answer

First order

Answer

Zero order

Answer

Second order

Question 55

A reaction is found to have a rate constant of 0.025 M⁻¹s⁻¹ at 25°C. If the temperature is increased to 50°C, what will happen to the rate constant?

Accepted Answer

The rate constant will increase.

Answer

The rate constant will remain the same.

Answer

The rate constant will decrease.

Answer

The rate constant will become zero.

Question 56

The following mechanism has been proposed for the reaction of NO₂ with CO: 
    Step 1: NO₂ + NO₂ → NO₃ + NO (slow)
    Step 2: NO₃ + CO → NO₂ + CO₂ (fast) 
    What is the rate law for this reaction?

Accepted Answer

Rate = k[NO₂]²

Answer

Rate = k[NO₃][CO]

Answer

Rate = k[NO][NO₂]

Answer

Rate = k[NO₂][CO]

Question 57

A reaction is found to be first order in reactant A. Doubling the concentration of A will:

Accepted Answer

Double the rate of the reaction.

Answer

Have no effect on the rate of the reaction.

Answer

Halve the rate of the reaction.

Answer

Quadruple the rate of the reaction.

Question 58

Which of the following statements is NOT true about the collision theory of reaction rates?

Accepted Answer

All collisions between reactant molecules lead to a reaction.

Answer

The rate of a reaction is proportional to the frequency of collisions between reactant molecules.

Answer

For a reaction to occur, the colliding molecules must have sufficient energy to overcome the activation energy barrier.