Here below some basic MCQ’s about “Order and Molecularity” with Answer which is explained in details. let’s check one by one which is given below.
Question 1
What is the order of a reaction if its rate is proportional to the concentration of one reactant raised to the power of 2?
A) 1
B) 2
C) 3
D) None of the above
Answer: B) 2
Explanation: The order of a reaction is determined by the sum of the powers of the concentration terms in the rate law. If the rate is proportional to the concentration of one reactant raised to the power of 2, the reaction is second-order with respect to that reactant.
Question 2
Which of the following statements is true regarding molecularity?
A) Molecularity can be a fractional value.
B) Molecularity refers to the number of molecules involved in the rate-determining step.
C) Molecularity is the sum of the orders of all reactants.
D) Molecularity can only be zero or a whole number.
Answer: B) Molecularity refers to the number of molecules involved in the rate-determining step.
Explanation: Molecularity is defined as the number of reactant molecules that collide simultaneously in an elementary reaction. It can only be a whole number (1, 2, 3, etc.) and cannot be fractional.
Question 3
A reaction has a rate law of Rate=k[A]1[B]2. What is the overall order of the reaction?
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order of the reaction is the sum of the exponents in the rate law. Here, it is 1+2=3.
Question 4
If a reaction is said to be zero-order, what does that imply about the concentration of the reactant?
A) The concentration of the reactant remains constant.
B) The reaction rate increases with the concentration of the reactant.
C) The reaction rate is dependent on the concentration of the reactant.
D) The reaction will stop once the concentration is zero.
Answer: A) The concentration of the reactant remains constant.
Explanation: In a zero-order reaction, the rate of reaction is constant and does not depend on the concentration of the reactants. Therefore, even if the concentration decreases, the rate remains the same until the reactants are depleted.
Question 5
Which of the following reactions is most likely to be bimolecular?
A) A → Products
B) A + B → Products
C) 2A → Products
D) A + B + C → Products
Answer: B) A + B → Products
Explanation: Bimolecular reactions involve two reactant molecules in the rate-determining step. The option A + B → Products indicates that two different molecules are involved, making it bimolecular. Option C could also be bimolecular if it involves two molecules of A colliding, but it is less clear than the direct two different reactants in option B.
Question 6
The molecularity of a reaction that involves the simultaneous collision of three reactant molecules is:
A) Unimolecular
B) Bimolecular
C) Trimolecular
D) Zero
Answer: C) Trimolecular
Explanation: Molecularity refers to the number of reactant molecules that participate in an elementary reaction. If three molecules collide simultaneously, the reaction is trimolecular.
Question 7
Which of the following rate laws indicates a first-order reaction?
A) Rate=k[A]0
B) Rate=k[A]1
C) Rate=k[A]2
D) Rate=k[A]3
Answer: B) Rate=k[A]1
Explanation: A first-order reaction has a rate that is directly proportional to the concentration of one reactant raised to the first power. Therefore, Rate=k[A]1 indicates a first-order reaction.
Question 8
In a reaction mechanism, which step is usually the slowest?
A) Fast step
B) Intermediate step
C) Rate-determining step
D) Catalytic step
Answer: C) Rate-determining step
Explanation: The rate-determining step is the slowest step in a reaction mechanism, which determines the overall rate of the reaction.
Question 9
What is the molecularity of a reaction represented by the equation 2A→Products?
A) 1
B) 2
C) 3
D) None of the above
Answer: B) 2
Explanation: In this reaction, two molecules of A are involved in the rate-determining step, making it bimolecular.
Question 10
Which of the following statements about zero-order reactions is true?
A) The reaction rate decreases as the reactant concentration decreases.
B) The reaction can proceed without any reactant.
C) The concentration of the reactant affects the rate.
D) The rate is constant regardless of the concentration of reactants.
Answer: D) The rate is constant regardless of the concentration of reactants.
Explanation: In a zero-order reaction, the rate is independent of the concentration of the reactants, remaining constant until the reactants are exhausted.
Question 11
A reaction is said to be second order if:
A) The rate is proportional to the square of the concentration of one reactant.
B) The rate is independent of the concentration of reactants.
C) The rate is proportional to the concentration of one reactant.
D) The rate is proportional to the sum of the concentrations of the reactants.
Answer: A) The rate is proportional to the square of the concentration of one reactant.
Explanation: A second-order reaction can either involve one reactant raised to the second power or two different reactants, each raised to the first power.
Question 12
Which of the following scenarios would likely result in a higher reaction rate?
A) Increased activation energy
B) Decreased temperature
C) Increased concentration of reactants
D) Increased volume
Answer: C) Increased concentration of reactants
Explanation: Increasing the concentration of reactants generally increases the frequency of collisions, which leads to a higher reaction rate.
Question 13
What type of reaction mechanism is represented by a single elementary step?
A) Complex mechanism
B) Overall reaction
C) Elementary reaction
D) Multi-step reaction
Answer: C) Elementary reaction
Explanation: An elementary reaction is a single step that describes a single reaction event, as opposed to a multi-step or complex mechanism.
Question 14
If doubling the concentration of a reactant in a first-order reaction results in a doubling of the rate, this is consistent with which of the following?
A) Zero order
B) First order
C) Second order
D) Third order
Answer: B) First order
Explanation: In a first-order reaction, the rate is directly proportional to the concentration of the reactant, so doubling the concentration will double the rate.
Question 15
A reaction’s rate constant kk increases with temperature due to:
A) Decreased activation energy
B) Increased frequency of collisions
C) Increased activation energy
D) Changes in molecularity
Answer: B) Increased frequency of collisions
Explanation: An increase in temperature generally increases the kinetic energy of the molecules, resulting in more frequent and more energetic collisions, which can enhance the rate of reaction.
Question 16
If a reaction is fourth order with respect to reactant A, how does the rate change if the concentration of A is tripled?
A) The rate increases by a factor of 3
B) The rate increases by a factor of 9
C) The rate increases by a factor of 27
D) The rate remains unchanged
Answer: C) The rate increases by a factor of 27
Explanation: For a fourth-order reaction, if the concentration of A is tripled, the rate increases by 34=8134=81, making it a factor of 81.
Question 17
Which reaction type is characterized by a rate that is independent of reactant concentration?
A) First-order reaction
B) Second-order reaction
C) Zero-order reaction
D) Pseudo-first-order reaction
Answer: C) Zero-order reaction
Explanation: In a zero-order reaction, the rate does not change with the concentration of the reactants, remaining constant until the reactants are exhausted.
Question 18
In the reaction A+B→C, if the rate law is Rate=k[A][B]2, what is the order with respect to reactant B?
A) 1
B) 2
C) 3
D) 0
Answer: B) 2
Explanation: The order of a reaction with respect to a reactant is given by the exponent of that reactant in the rate law. Here, the exponent of B is 2.
Question 19
For a bimolecular reaction, the molecularity can be defined as:
A) 1
B) 2
C) 3
D) 0
Answer: B) 2
Explanation: Bimolecular reactions involve two molecules colliding in the rate-determining step, so the molecularity is 2.
Question 20
If a reaction has an activation energy of 50 kJ/mol and is run at a higher temperature, what effect will this have on the rate constant k?
A) k will decrease
B) k will remain the same
C) k will increase
D) Cannot be determined
Answer: C) k will increase
Explanation: Generally, an increase in temperature leads to an increase in the rate constant k due to the Arrhenius equation, which states that k increases exponentially with temperature.
Question 21
If the rate of a reaction quadruples when the concentration of one reactant is doubled, what is the order of the reaction with respect to that reactant?
A) 1
B) 2
C) 3
D) 4
Answer: B) 2
Explanation: If doubling the concentration of a reactant results in a fourfold increase in the rate, the reaction is second order with respect to that reactant, since (22)=4
Question 22
In a first-order reaction, which of the following is true?
A) The half-life is dependent on the initial concentration.
B) The half-life is constant and independent of concentration.
C) The rate decreases linearly with time.
D) The reaction must have a catalyst to proceed.
Answer: B) The half-life is constant and independent of concentration.
Explanation: In first-order reactions, the half-life remains constant regardless of the initial concentration of the reactants.
Question 23
A reaction has a molecularity of 1. This means the reaction is:
A) Bimolecular
B) Unimolecular
C) Trimolecular
D) None of the above
Answer: B) Unimolecular
Explanation: A reaction with a molecularity of 1 involves only one reactant molecule in the rate-determining step, making it unimolecular.
Question 24
What is the unit of the rate constant kk for a second-order reaction?
A) M/s
B) M²/s
C) 1/M·s
D) M/s²
Answer: C) 1/M·s
Explanation: For a second-order reaction, the rate constant
k has units of 1/(M·s), reflecting that the rate depends on the concentration squared.
Question 25
Which of the following factors does NOT affect the rate of a chemical reaction?
A) Temperature
B) Concentration of reactants
C) Presence of a catalyst
D) Color of the reactants
Answer: D) Color of the reactants
Explanation: The color of the reactants does not influence the rate of a chemical reaction. The rate is affected by temperature, concentration, and catalysts.
Question 26
In a reaction where the rate is Rate=k[A]2[B], the overall order of the reaction is:
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order is the sum of the exponents in the rate law: 2+1=3
Question 27
If a reaction has a molecularity of 3, it is most likely:
A) Unimolecular
B) Bimolecular
C) Termolecular
D) Zero order
Answer: C) Termolecular
Explanation: A reaction with a molecularity of 3 involves three reactant molecules and is referred to as termolecular.
Question 28
Which of the following is an example of a zero-order reaction?
A) A→Products
B) A+B→Products
C) 2A→Products
D) None of the above
Answer: A) A→Products
Explanation: A zero-order reaction can proceed without any dependence on the concentration of reactants, making it consistent with the scenario provided.
Question 30
A reaction with a half-life that depends on the initial concentration is most likely:
A) Zero-order
B) First-order
C) Second-order
D) Third-order
Answer: C) Second-order
Explanation: In second-order reactions, the half-life is inversely proportional to the initial concentration, meaning it changes as the concentration changes.
Question 31
If the rate of a reaction doubles when the concentration of reactant A is doubled, the reaction is:
A) Zero-order
B) First-order
C) Second-order
D) Third-order
Answer: B) First-order
Explanation: A reaction is first-order if doubling the concentration of one reactant results in a doubling of the rate.
Question 32
In an elementary reaction, which of the following describes the relationship between molecularity and order?
A) Molecularity and order are always equal.
B) Molecularity can be fractional, but order cannot.
C) Molecularity is always greater than order.
D) They are not necessarily related.
Answer: D) They are not necessarily related.
Explanation: Molecularity refers to the number of molecules in an elementary step, while order is based on the rate law and can be influenced by various factors.
Question 33
If a catalyst is added to a reaction, what is the likely effect on the activation energy?
A) It increases.
B) It decreases.
C) It remains the same.
D) It becomes undefined.
Answer: B) It decreases.
Explanation: Catalysts provide an alternative reaction pathway with a lower activation energy, thereby increasing the rate of the reaction.
Question 34
Which of the following is a characteristic of a first-order reaction?
A) Rate is constant
B) Half-life is dependent on initial concentration
C) Rate doubles with concentration doubling
D) Molecularity can be zero
Answer: C) Rate doubles with concentration doubling
Explanation: In first-order reactions, the rate is directly proportional to the concentration of the reactant, so doubling the concentration doubles the rate.
Question 35
In a reaction that is third order overall, which of the following could be a possible rate law?
A) Rate=k[A]3
B) Rate=k[A][B]
C) Rate=k[A]2[B]
D) All of the above
Answer: D) All of the above
Explanation: All the given options can sum to an overall order of 3 depending on the combinations of reactants involved.
Question 36
Which of the following reactions would likely be unimolecular?
A) A+B→C
B) 2A→Products
C) A→Products
D) A+2B→C
Answer: C) A→Products
Explanation: A unimolecular reaction involves only one reactant molecule in the rate-determining step.
Question 37
For a reaction to be classified as bimolecular, it must involve:
A) One molecule
B) Two molecules colliding
C) Three molecules
D) Any number of molecules
Answer: B) Two molecules colliding
Explanation: Bimolecular reactions involve the simultaneous collision of two reactant molecules in the rate-determining step.
Question 38
Which of the following scenarios could represent a second-order reaction?
A) 2A→Products
B) A+B→Products
C) A+A→Products
D) Both A and C
Answer: D) Both A and C
Explanation: Both 2A→Products and A+A→Products are examples of reactions that could be second-order, involving two molecules of A.
Question 39
If a reaction’s rate is described by Rate=k[A]3[B]0, what can be concluded about reactant B?
A) It is involved in the reaction.
B) It has no effect on the reaction rate.
C) It is a catalyst.
D) It is in excess.
Answer: B) It has no effect on the reaction rate.
Explanation: The exponent of B is 0, meaning that changes in the concentration of B do not affect the rate of the reaction.
Question 40
The reaction A+2B→Products has a rate law of Rate=k[A]1[B]2. What is the overall order?
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order is the sum of the exponents in the rate law: 1+2=3.
Question 41
In a chemical reaction, if the rate of reaction is dependent on the square of the concentration of A, the reaction is classified as:
A) Zero-order
B) First-order
C) Second-order
D) Third-order
Answer: C) Second-order
Explanation: A reaction that depends on the square of the concentration of one reactant (e.g., Rate=k[A]2 is classified as second-order with respect to that reactant.
Question 42
The rate of a chemical reaction increases with temperature because:
A) The molecules collide less frequently.
B) The activation energy decreases.
C) The average kinetic energy of the molecules increases.
D) The concentration of reactants decreases.
Answer: C) The average kinetic energy of the molecules increases.
Explanation: An increase in temperature raises the kinetic energy of molecules, leading to more frequent and energetic collisions, which increases the reaction rate.
Question 43
A reaction mechanism consists of multiple steps. The rate of the overall reaction is determined by:
A) The fast step
B) The slowest step
C) The intermediate step
D) The first step
Answer: B) The slowest step
Explanation: The overall rate of a reaction is determined by the rate-determining step, which is the slowest step in the mechanism.
Question 44
For a first-order reaction, if the concentration of the reactant decreases from 0.1 M to 0.05 M, the rate will:
A) Stay the same
B) Double
C) Halve
D) Decrease by a factor of 4
Answer: C) Halve
Explanation: For a first-order reaction, the rate is directly proportional to the concentration of the reactant. If the concentration is halved, the rate also halves.
Question 45
The reaction A+2B→C has a rate law of Rate=k[A]2[B]. What is the reaction order with respect to A?
A) 1
B) 2
C) 3
D) 4
Answer: B) 2
Explanation: The order with respect to A is given by the exponent in the rate law, which is 2.
Question 46
If a reaction is found to have an activation energy of 75 kJ/mol, what effect would increasing the temperature have on the reaction?
A) No effect on rate
B) Decrease the rate
C) Increase the rate
D) Change the activation energy
Answer: C) Increase the rate
Explanation: Increasing the temperature typically increases the rate of a reaction by providing more molecules with enough energy to overcome the activation energy barrier.
Question 47
What is the overall order of the reaction represented by the rate law Rate=k[A][B]2?
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order of the reaction is the sum of the exponents in the rate law: 1+2=3
Question 48
Which of the following reactions would most likely be zero-order?
A) A→Products with a constant rate
B) 2A→Products
C) A+B→Products
D) A+2B→Products
Answer: A) A→Products with a constant rate
Explanation: A zero-order reaction has a constant rate that does not depend on the concentration of the reactant(s).
Question 49
In a reaction mechanism, the species that is formed in one step and consumed in a subsequent step is called:
A) Catalyst
B) Intermediate
C) Reactant
D) Product
Answer: B) Intermediate
Explanation: Intermediates are species that are formed during the reaction mechanism but do not appear in the overall balanced equation.
Question 50
For a reaction that is second-order with respect to reactant A, the half-life is:
A) Constant and independent of initial concentration
B) Inversely proportional to initial concentration
C) Directly proportional to initial concentration
D) Unrelated to the concentration
Answer: B) Inversely proportional to initial concentration
Explanation: In second-order reactions, the half-life is inversely proportional to the initial concentration of the reactant.
Question 51
In a reaction mechanism, the step with the highest activation energy is known as:
A) The fast step
B) The rate-determining step
C) The intermediate step
D) The catalytic step
Answer: B) The rate-determining step
Explanation: The rate-determining step is the slowest step with the highest activation energy, which limits the overall reaction rate.
Question 52
If the rate of a reaction is found to be dependent on the concentration of two different reactants, it indicates that the reaction is:
A) Unimolecular
B) Bimolecular
C) Trimolecular
D) Zero-order
Answer: B) Bimolecular
Explanation: A bimolecular reaction involves two reactant molecules in the rate-determining step, reflecting that the rate is dependent on the concentrations of both.
Question 53
The activation energy for a reaction can be lowered by:
A) Increasing the temperature
B) Increasing the concentration
C) Adding a catalyst
D) Decreasing the volume
Answer: C) Adding a catalyst
Explanation: Catalysts lower the activation energy barrier for a reaction, increasing the reaction rate without being consumed in the process.
Question 54
For a zero-order reaction, what is the relationship between concentration and time?
A) Linear
B) Exponential
C) Inversely proportional
D) Quadratic
Answer: A) Linear
Explanation: In a zero-order reaction, the concentration decreases linearly over time, as the rate is constant regardless of the concentration.
Question 55
If the rate law of a reaction is Rate=k[A]1[B]1, what is the overall order of the reaction?
A) 1
B) 2
C) 3
D) 4
Answer: B) 2
Explanation: The overall order is the sum of the exponents: 1+1=2.
Question 56
What effect does a catalyst have on the equilibrium constant of a reaction?
A) Increases it
B) Decreases it
C) Does not affect it
D) Changes it based on concentration
Answer: C) Does not affect it
Explanation: Catalysts speed up the rate at which equilibrium is reached but do not change the position of equilibrium or the equilibrium constant.
Question 57
In a reaction where the rate is given by Rate=k[A]2, if the concentration of A is halved, the rate will:
A) Stay the same
B) Halve
C) Quarter
D) Double
Answer: C) Quarter
Explanation: If the concentration of A is halved, the rate will decrease by a factor of (1/2)2=1/4
Question 58
A reaction mechanism that has two elementary steps, where the first step is fast and the second step is slow, is known as:
A) An overall mechanism
B) A complex mechanism
C) A simple mechanism
D) A chain mechanism
Answer: B) A complex mechanism
Explanation: A mechanism with multiple steps, particularly where one is slow, is considered complex because it involves interactions between multiple species.
Question 59
Which of the following would be classified as a unimolecular reaction?
A) A+B→C
B) A→Products
C) 2A+B→C
Answer: B) A→Products
Explanation: A unimolecular reaction involves only one reactant molecule in the rate-determining step.
Question 60
In a first-order reaction, the half-life is defined as the time required for the concentration of the reactant to:
A) Decrease to zero
B) Double
C) Decrease to half its initial value
D) Increase to double its value
Answer: C) Decrease to half its initial value
Explanation: The half-life of a first-order reaction is the time it takes for the concentration of the reactant to reduce to half of its initial concentration.
Question 61
If the reaction rate is found to be constant over time, the reaction is most likely:
A) First-order
B) Second-order
C) Zero-order
D) Pseudo-first-order
Answer: C) Zero-order
Explanation: In a zero-order reaction, the rate remains constant regardless of the concentration of the reactants until they are depleted.
Question 62
The half-life of a zero-order reaction is:
A) Independent of initial concentration
B) Directly proportional to initial concentration
C) Inversely proportional to initial concentration
D) Constant
Answer: B) Directly proportional to initial concentration
Explanation: In a zero-order reaction, the half-life increases as the initial concentration increases.
Question 63
For the reaction 2A+B→C, if the rate law is Rate=k[A]2[B], what is the order of the reaction with respect to B?
A) 1
B) 2
C) 3
D) 4
Answer: A) 1
Explanation: The order with respect to B is given by the exponent in the rate law, which is 1.
Question 64
Which of the following factors will NOT affect the activation energy of a reaction?
A) Nature of the reactants
B) Temperature
C) Presence of a catalyst
D) Reaction pathway
Answer: B) Temperature
Explanation: While temperature affects the rate of reaction, it does not change the inherent activation energy of the reaction itself.
Question 66
For a reaction with an overall order of 3, which of the following rate laws is possible?
A) Rate=k[A]1[B]2
B) Rate=k[A]3
C) Rate=k[A]2[B]1
D) All of the above
Answer: D) All of the above
Explanation: All the given options represent valid rate laws that can sum to an overall order of 3.
Question 67
The molecularity of a reaction is always a whole number. This is because:
A) It represents the stoichiometry of the overall reaction.
B) It describes the concentration of reactants.
C) It reflects the number of molecules involved in an elementary step.
D) It is derived from the rate constant.
Answer: C) It reflects the number of molecules involved in an elementary step.
Explanation: Molecularity refers to the number of reactant molecules in the elementary step, which must be a whole number.
Question 68
If a reaction is second order in respect to A and zero order in respect to B, which of the following rate laws is correct?
A) Rate=k[A]2[B]1
B) Rate=k[A]2[B]0
C) Rate=k[A]1[B]2
D) Rate=k[A]0[B]0
Answer: B) Rate=k[A]2[B]0
Explanation: The rate law must reflect the orders correctly; since B is zero-order, it contributes nothing to the rate.
Question 69
In a second-order reaction, if the half-life of the reaction is known, it can be expressed as:
A) 0.693kk0.693
B) 1k[A]0k[A]01
C) 2kk2
D) 12k2k1
Answer: B) 1k[A]0k[A]01
Explanation: The half-life of a second-order reaction is inversely proportional to the initial concentration of the reactant.
Question 70
Which of the following is true regarding molecularity?
A) It can be a fraction.
B) It can be zero.
C) It is determined from the rate law.
D) It refers only to the slowest step in a mechanism.
Answer: D) It refers only to the slowest step in a mechanism.
Explanation: Molecularity is specifically defined for elementary reactions, reflecting the number of molecules involved in the rate-determining step.
Question 71
In an elementary reaction, if two reactant molecules collide, the reaction is classified as:
A) Unimolecular
B) Bimolecular
C) Trimolecular
D) Zero-order
Answer: B) Bimolecular
Explanation: A bimolecular reaction involves the collision of two molecules in the rate-determining step.
Question 72
A catalyst works by:
A) Increasing the activation energy
B) Providing an alternative pathway with lower activation energy
C) Changing the equilibrium constant
D) Reacting with the products
Answer: B) Providing an alternative pathway with lower activation energy
Explanation: Catalysts lower the activation energy, allowing reactions to proceed more quickly without being consumed in the process.
Question 73
If a first-order reaction has a half-life of 10 minutes, what will be the concentration after 20 minutes?
A) Half of the initial concentration
B) One-fourth of the initial concentration
C) One-eighth of the initial concentration
D) One-sixteenth of the initial concentration
Answer: B) One-fourth of the initial concentration
Question 74
For the reaction 3A→B, the molecularity is:
A) 1
B) 2
C) 3
D) None of the above
Answer: C) 3
Explanation: The molecularity refers to the number of molecules involved in the reaction, so for this reaction, it is three (3A).
Question 75
The rate of a reaction is influenced by:
A) Concentration
B) Temperature
C) Presence of a catalyst
D) All of the above
Answer: D) All of the above
Explanation: All these factors can influence the rate of a chemical reaction.
Question 76
In the reaction mechanism, which of the following steps is usually the slowest?
A) Fast step
B) Rate-determining step
C) Catalytic step
D) Intermediate step
Answer: B) Rate-determining step
Explanation: The rate-determining step is the slowest step and limits the overall rate of the reaction.
Question 77
The overall order of the reaction is:
A) The sum of the molecularities of the reactants
B) The sum of the exponents in the rate law
C) The average of the exponents in the rate law
D) Always a whole number
Answer: B) The sum of the exponents in the rate law
Explanation: The overall order of the reaction is calculated by summing the powers of the concentrations in the rate law.
Question 78
For a reaction that is zero-order in respect to a reactant, what happens to the rate if the concentration is increased?
A) The rate increases.
B) The rate decreases.
C) The rate remains unchanged.
D) The rate becomes negative.
Answer: C) The rate remains unchanged.
Explanation: In a zero-order reaction, the rate is constant and does not depend on the concentration of the reactants.
Question 79
In a bimolecular reaction, if the concentration of one reactant is doubled, how does this affect the reaction rate?
A) The rate is unchanged.
B) The rate doubles.
C) The rate triples.
D) The rate quadruples.
Answer: B) The rate doubles.
Explanation: If the reaction is bimolecular and the concentration of one reactant is doubled, the reaction rate will double as well.
Question 80
The reaction 2A+B→C has a rate law of Rate=k[A]1[B]2 What is the order of the reaction with respect to A and B?
A) 1 for A and 2 for B
B) 2 for A and 1 for B
C) 1 for A and 3 for B
D) 3 for both
Answer: A) 1 for A and 2 for B
Explanation: The orders with respect to A and B are indicated by the exponents in the rate law.
Question 81
In the reaction mechanism, if an intermediate is formed, it will:
A) Appear in the final products
B) Not appear in the final reaction equation
C) Be consumed in the same step it is produced
D) Be a catalyst
Answer: B) Not appear in the final reaction equation
Explanation: Intermediates are produced and consumed in the reaction mechanism but do not appear in the overall balanced equation.
Question 82
The rate constant kk for a reaction is affected by:
A) Temperature only
B) Concentration only
C) Pressure only
D) Temperature and concentration
Answer: A) Temperature only
Explanation: The rate constant kk is dependent on temperature; changes in temperature can significantly alter kk.
Question 83
In a first-order reaction, if the rate constant kk is 0.1 s−1−1, what will be the half-life?
A) 6.93 s
B) 10 s
C) 20 s
D) 0.693 s
Answer: A) 6.93 s
Question 84
If a reaction’s rate is given as Rate=k[A]1[B]1[C]1, the overall reaction order is:
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order is the sum of the exponents: 1+1+1=3
Question 85
Which of the following is a characteristic feature of second-order reactions?
A) The rate is independent of concentration.
B) The half-life is dependent on the initial concentration.
C) The rate increases linearly with time.
D) The concentration of the reactants decreases exponentially.
Answer: B) The half-life is dependent on the initial concentration.
Explanation: For second-order reactions, the half-life increases as the initial concentration decreases.
Question 86
What will happen to the rate of a reaction if the temperature is increased?
A) It will always decrease.
B) It will remain the same.
C) It will increase due to more energetic collisions.
D) It will fluctuate unpredictably.
Answer: C) It will increase due to more energetic collisions.
Explanation: Increasing temperature generally increases molecular energy, leading to more frequent and effective collisions.
Question 87
In a reaction that is third-order overall, which of the following is NOT a valid rate law?
A) Rate=k[A]3
B) Rate=k[A]2[B]1
C) Rate=k[A]1[B]2[C]0
D) Rate=k[A]1[B]1[C]1
Answer: D) Rate=k[A]1[B]1[C]1
Explanation: The option D adds up to an order of 3, but it requires three different reactants which can be misleading in a third-order context.
Question 88
Which of the following would NOT typically be classified as a reaction intermediate?
A) A product formed in an early step
B) A reactant that appears in the rate-determining step
C) A species that is formed and consumed in subsequent steps
D) A catalyst
Answer: D) A catalyst
Explanation: A catalyst is not consumed in the reaction and facilitates the process but does not appear as an intermediate.
Question 89
For a reaction that is second-order with respect to reactant A, what is the relationship between concentration and rate?
A) Linear
B) Exponential
C) Quadratic
D) Logarithmic
Answer: C) Quadratic
Explanation: In second-order reactions, the rate is proportional to the square of the concentration of A, leading to a quadratic relationship.
Question 90
In the reaction A+B→CA+B→C, if the rate law is Rate=k[A]1[B]2Rate=k[A]1[B]2, which reactant is in excess?
A) A
B) B
C) C
D) None of the above
Answer: B) B
Explanation: Since B has a higher order in the rate law, it suggests that it is likely present in excess to maintain the rate.
Question 91
For a zero-order reaction, if the initial concentration is 0.4 M and the rate constant kk is 0.1 M/s, how long will it take for the concentration to reach 0?
A) 2 s
B) 4 s
C) 8 s
D) 16 s
Answer: B) 4 s
Question 92
In an elementary reaction, what does the term “molecularity” refer to?
A) The total number of products formed
B) The number of reactant molecules involved in the step
C) The rate of the reaction
D) The temperature at which the reaction occurs
Answer: B) The number of reactant molecules involved in the step
Explanation: Molecularity specifically refers to how many molecules are involved in an elementary step of the reaction.
Question 93
The rate constant kk for a reaction is influenced by:
A) The concentration of reactants
B) The temperature
C) The presence of catalysts
D) Both B and C
Answer: D) Both B and C
Explanation: The rate constant is primarily influenced by temperature and the presence of catalysts.
Question 94
If the rate law is given as Rate=k[A]0[B]1Rate=k[A]0[B]1, what can be concluded about reactant A?
A) It has no effect on the rate.
B) It increases the rate significantly.
C) It is the limiting reactant.
D) It is the catalyst.
Answer: A) It has no effect on the rate.
Explanation: A concentration raised to the power of zero means it does not influence the rate of the reaction.
Question 95
In a bimolecular reaction, if the concentration of both reactants is doubled, how does the rate change?
A) It remains the same
B) It doubles
C) It quadruples
D) It increases eightfold
Answer: C) It quadruples
Question 96
In the context of reaction kinetics, what is meant by “order of a reaction”?
A) The number of reactants
B) The power to which the concentration of a reactant is raised in the rate law
C) The total time required for the reaction
D) The speed of the reaction
Answer: B) The power to which the concentration of a reactant is raised in the rate law
Explanation: The order of a reaction refers to the exponents in the rate law, indicating how the rate depends on the concentration of each reactant.
Question 97
If a reaction’s rate is described by Rate=k[A]2[B]0Rate=k[A]2[B]0, which of the following statements is true?
A) The reaction is zero-order with respect to A.
B) The reaction is first-order with respect to B.
C) The concentration of B has no effect on the rate.
D) The reaction is second-order with respect to both A and B.
Answer: C) The concentration of B has no effect on the rate.
Explanation: Since B has an exponent of 0, its concentration does not influence the rate of the reaction.
Question 98
For a reaction that is first-order, the integrated rate law can be expressed as:
A) [A]=[A]0−kt
B) [A]=[A]0e−kt
C) ln[A]=ln[A]0−kt
D) Both B and C
Answer: D) Both B and C
Explanation: Both expressions represent the integrated rate laws for first-order reactions.
Question 99
The units of the rate constant kk for a zero-order reaction are:
A) M/s
B) M²/s
C) 1/M·s
D) M/s²
Answer: A) M/s
Explanation: For zero-order reactions, the rate is constant and the unit of kk is concentration per time, which is M/s.
Question 100
In the context of chemical kinetics, which statement is correct?
A) Molecularity can be a fraction.
B) The order of a reaction is always equal to its molecularity.
C) The rate constant changes with concentration.
D) Molecularity is defined for elementary reactions only.
Answer: D) Molecularity is defined for elementary reactions only.
Explanation: Molecularity is specific to elementary steps in a reaction mechanism and cannot be a fraction.
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