Chemical Kinetics

Question 1

Define chemical kinetics

Answer 1

Chemical kinetics is the study of the rate at which chemical reactions occur and the factors that affect these rates.

Question 2

What is reaction rate?

Answer 2

Reaction rate is the change in concentration of a reactant or product per unit time.

Question 3

Write the general rate equation for a reaction aA + bB → cC + dD.

Answer 3

Rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the reaction orders with respect to A and B.

Question 4

Define order of reaction

Answer 4

Order of reaction is the sum of the powers of the concentration terms in the rate law equation.

Question 5

What is a zero-order reaction?

Answer 5

A reaction whose rate is independent of the concentration of the reactants.

Question 6

Give an example of a first-order reaction.

Answer 6

Radioactive decay is an example of a first-order reaction.

Question 7

How is the rate constant (k) determined?

Answer 7

The rate constant can be determined experimentally by measuring the rate of reaction at different concentrations of reactants.

Question 8

What is the integrated rate law for a zero-order reaction?

Answer 8

[A] = [A]₀ - kt

Question 9

Write the integrated rate law for a first-order reaction.

Answer 9

ln[A] = ln[A]₀ - kt or [A] = [A]₀e^(-kt)

Question 10

Give the integrated rate law for a second-order reaction.

Answer 10

1/[A] = 1/[A]₀ + kt

Question 11

Define half-life of a reaction

Answer 11

Half-life is the time required for the concentration of a reactant to decrease to half of its initial concentration.

Question 12

What is the half-life formula for a first-order reaction?

Answer 12

t₁/₂ = 0.693/k

Question 13

How does the half-life of a second-order reaction depend on the initial concentration?

Answer 13

t₁/₂ = 1/(k[A]₀), indicating it is inversely proportional to the initial concentration.

Question 14

State the Arrhenius equation

Answer 14

k = A e^(-Ea/RT), where A is the frequency factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin.

Question 15

How does the rate constant change with temperature

Answer 15

The rate constant increases with an increase in temperature

Question 16

What is activation energy?

Answer 16

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

Question 17

What is the collision theory?

Answer 17

Collision theory states that for a reaction to occur, reactant molecules must collide with sufficient energy and proper orientation.

Question 18

Define the transition state

Answer 18

The transition state is a high-energy, unstable state that occurs during the transformation of reactants into products.

Question 19

Explain the concept of the activated complex.

Answer 19

The activated complex is a temporary, intermediate structure formed during the conversion of reactants into products.

Question 20

What is a catalyst?

Answer 20

A catalyst is a substance that increases the rate of a reaction without being consumed in the process.

Question 21

How do catalysts affect activation energy?

Answer 21

Catalysts lower the activation energy of a reaction.

Question 22

Differentiate between homogeneous and heterogeneous catalysts.

Answer 22

Homogeneous catalysts are in the same phase as the reactants, while heterogeneous catalysts are in a different phase.

Question 23

What is a reaction mechanism?

Answer 23

A reaction mechanism is a step-by-step sequence of elementary reactions by which overall chemical change occurs.

Question 24

Define elementary reaction

Answer 24

An elementary reaction is a single step reaction with a single transition state.

Question 25

What is the rate-determining step?

Answer 25

The rate-determining step is the slowest step in a reaction mechanism that determines the overall reaction rate.

Question 26

List the factors affecting reaction rates.

Answer 26

Concentration of reactants, temperature, presence of a catalyst, and surface area of reactants.

Question 27

How does concentration affect reaction rate?

Answer 27

Generally, increasing the concentration of reactants increases the rate of reaction

Question 28

Why does increasing temperature usually increase reaction rate?

Answer 28

Higher temperatures increase the kinetic energy of molecules, leading to more frequent and energetic collisions.

Question 29

Explain the effect of surface area on reaction rate

Answer 29

Increasing the surface area of reactants exposes more particles to collisions, increasing the reaction rate.

Question 30

What is the difference between average rate and instantaneous rate?

Answer 30

The average rate is the change in concentration over a long time interval, while the instantaneous rate is the rate at a specific moment in time.

Question 31

What is the steady-state approximation?

Answer 31

The steady-state approximation assumes that the concentration of intermediate species remains constant throughout the reaction

Question 32

Give an example of a pseudo-first-order reaction.

Answer 32

Hydrolysis of esters in the presence of a large excess of water.

Question 33

What is a rate-determining step in a reaction mechanism?

Answer 33

It is the slowest step in the mechanism that determines the overall rate of the reaction.

Question 34

Explain the role of a catalyst in the ozone depletion reaction.

Answer 34

Chlorine radicals (Cl•) act as a catalyst in the decomposition of ozone (O3) in the stratosphere

Question 35

What is the Michaelis-Menten equation in enzyme kinetics?

Answer 35

v = (Vmax[S]) / (Km + [S]), where v is the reaction rate, Vmax is the maximum rate, [S] is the substrate concentration, and Km is the Michaelis constant.

Question 36

Define molecularity of a reaction

Answer 36

Molecularity is the number of reactant molecules involved in an elementary step of the reaction.

Question 37

What is the difference between molecularity and order of reaction?

Answer 37

Molecularity is specific to an elementary step and is always an integer, while the order of reaction is determined experimentally and can be fractional.

Question 38

Describe an example of a second-order reaction.

Answer 38

The reaction 2NO + O2 → 2NO2 is an example of a second-order reaction

Question 39

What is the Lindemann mechanism?

Answer 39

It is a mechanism to explain unimolecular reactions through a two-step process involving the formation of an energized intermediate.

Question 40

How is the rate constant for a reaction determined using the Arrhenius plot?

Answer 40

By plotting ln(k) versus 1/T and finding the slope, which is equal to -Ea/R.

Question 41

What is a chain reaction? Provide an example.

Answer 41

: A chain reaction involves a sequence of reactions where a reactive intermediate regenerates in subsequent steps. Example: the hydrogen-bromine reaction (H2 + Br2 → 2HBr).