Reaction Kinetics MCQs with Answers
If iron is not 100% pure, which of the following best describes the reaction rate?
2Fe + 3H₂O + O₂ → Fe₂O₃·3H₂O
Very fast reaction
Very slow reaction
Moderately reaction
Not predicted
Which of the following reactions is usually slow?
Neutralization of acids and bases
Explosive reaction of O₂ and H₂
Organic substitution reaction
Photochemical reactions
For a chemical reaction to take place:
The vessel shall be open
Reacting molecules should have less energy than Ea at time of collision
Reacting molecules must be properly oriented and have energy equal to or greater than Ea
The reacting molecules must not collide with each other
The reaction rate increases due to a temperature rise from 10 K to 100 K. What is the resulting increase in rate?
By increasing the concentration of reactants, the reaction rate:
Decreases
Increases
Remains constant
Not predicted
Select the correct rate law from given data
The following table:
Rate=k[A][B]
Rate = k[A]²[B]
Rate = k[A]⁰[B]²
Rate = k[A][B]²
The rate of a reaction involving ions can be studied using:
Spectrometric method
Dilatometric method
Optical rotation method
Electrical conductivity method
Which method is useful for determining the rate of reactions that involve small volume changes in solutions?
Refractometric method
Dilatometric method
Optical rotation method
Spectrometric method
Which rate determination method is suitable for reactions in solutions where changes in refractive index occur?
Dilatometric method
Optical rotation method
Refractometric method
Spectrometric method
The specific rate constant of a chemical reaction is the reaction rate when the concentration of the reactant is:
Less than unity
Greater than unity
Equal to unity
Equal to the concentration of 2nd order reaction
What is the unit of the rate constant for a third-order reaction?
dm⁶ mol⁻² sec⁻¹
sec⁻¹
mol⁻² dm⁺⁶
dm³ mol⁻¹ sec⁻¹
A second-order reaction behaves like a first-order reaction when:
One of the reactants is limiting
One of the reactants is in large excess
None of the reactants is in large excess
Both reactants in large excess
The half-life of a first-order decomposition reaction for a substance dissolved in CCl₄ is 2.5 hours at 30°C. If the initial mass of the substance is 160 g, how much will remain after 10 hours?
The hydrolysis of ethyl acetate into acetic acid and ethanol in the presence of a mineral acid follows which reaction order?
Zero order reaction
Pseudo 1st order reaction
1st order reaction
2nd order reaction
For the reaction A + 2B ⟶ C, the rate law is given by Rate = k[A]. What is the order of the reaction?
For the reaction A ⟶ B, the rate of reaction doubles when the concentration of A is increased four times. The order of the reaction with respect to A is:
The rate of a reaction increases by a factor of 8 when the concentration of the reactant is doubled and by a factor of 27 when the concentration is tripled. What is the order of the reaction?
The slowest step in a multi-step reaction that determines the overall reaction rate is called the
Intermediate step
Rate determining step
Fast step
Equilibrium step
Which of the following factors does NOT affect the rate of a chemical reaction?
Concentration of reactants
Temperature
Color of the reactants
Presence of a catalyst
The rate of a reaction is defined as:
Change in pressure per unit time
Change in concentration of reactant or product per unit time
Time taken for reaction to complete
Amount of product formed at the end
What are the units of the rate of reaction when concentration is in mol dm⁻³ and time in seconds?
mol dm⁻³ s
mol dm⁻³ s⁻¹
mol s⁻¹
mol dm⁻¹ s⁻¹
The instantaneous rate of reaction is:
Average rate over a long time interval
Rate at a particular moment in time
Rate at the start of the reaction only
Rate at the end of the reaction only
According to the law of mass action, the rate of reaction is proportional to:
The sum of concentrations of reactants
The product of the concentrations of reactants raised to their powers
The difference in concentration of reactants and products
The total volume of the reaction mixture
In the rate equation Rate=k[A]ᵐ[B]ⁿ , the exponents m and n represent:
Stoichiometric coefficients
Orders of reaction with respect to A and B
Molecular weights of A and B
Rate constants
The overall order of the reaction 2A+B→products with rate law Rate=k[A]²[B]¹ is:
The order of a reaction can be:
Only zero or positive integers
Only negative integers
All of them
Only fractions
A reaction whose rate is independent of the concentration of reactants is called:
First order
Second order
Zero order
Pseudo first order
The half-life of a first order reaction:
Depends on the initial concentration
Is independent of the initial concentration
Increases with increasing concentration
Decreases with decreasing temperature
The half-life of a second order reaction is:
Independent of initial concentration
Directly proportional to initial concentration
Inversely proportional to initial concentration
Constant at all times
For a third order reaction, the half-life is:
Independent of concentration
Inversely proportional to the square of initial concentration
Directly proportional to initial concentration
Equal to that of a first order reaction
Which of the following is true about the rate constant k?
It changes with concentration but not temperature
It remains constant regardless of temperature
It changes with temperature but not concentration
It depends on the volume of the reaction mixture
The rate equation for the decomposition of nitrogen pentoxide (N₂O₅) is experimentally found to be:
Rate = k[N₂O₅]²
Rate = k[N₂O₅]
Rate = k[N₂O₅]¹ᐟ²
Rate = k[N₂O₅]⁰
A pseudo first order reaction is characterized by:
Rate depends on two reactants equally
Rate depends only on one reactant because other reactant is in large excess
Rate is zero order
Rate depends only on products
The reaction intermediate is:
A stable product formed at the end
A species formed temporarily during the reaction mechanism
The reactant molecule
The catalyst
For the reaction 2NO₂ + CO → NO + CO₂ + NO₃, the rate law is found to be:
Rate = k[NO₂][CO]
Rate = k[NO₂]²
Rate = k[CO]²
Rate = k[NO₃]
The units of the rate constant for a second order reaction are:
s⁻¹
mol dm⁻³ s⁻¹
dm³ mol⁻¹ s⁻¹
mol dm³ s
The rate of reaction decreases with time because:
Temperature decreases
Concentration of reactants decreases
Products inhibit the reaction
Catalyst is consumed
The half-life period of a radioactive isotope undergoing first order decay is:
Dependent on the amount of isotope present
Independent of the amount of isotope present
Inversely proportional to the amount of isotope
Variable with pressure
The order of reaction is experimentally determined by:
Balancing the chemical equation
Measuring how rate changes with concentration
Calculating molecular weights
Observing color change
The rate determining step in a reaction mechanism is:
The fastest step
The step with the highest activation energy
The slowest step
The last step
If a reaction has rate law Rate = k[A]¹ᐟ², the order of reaction is:
For a zero order reaction, the rate is:
Directly proportional to concentration
Independent of concentration
Proportional to square of concentration
Inversely proportional to concentration
The rate constant for a reaction at a given temperature is:
Dependent on initial concentrations
Independent of initial concentrations
Dependent on volume of container
Variable with pressure only
The rate law for the reaction 2FeCl₃ + 6KI → 2FeI₃ + 6KCl + I₂ is experimentally found to be:
Rate = k[FeCl₃]²[KI]¹
Rate = k[FeCl₃][KI]²
Rate = k[FeCl₃][KI]
Rate = k[FeCl₃]³[KI]³
The half-life of a second order reaction is given by:
t₁/₂ = 0.693/k
t₁/₂ = 1/k.a
t₁/₂ = 1/k.a²
t₁/₂ = k.a
The rate of a reaction is measured by:
Change in volume per time
Change in concentration per time
Change in mass per time
Change in color intensity per time
In a reaction where the rate law is Rate = k[A]¹[B]⁰ , the overall order is:
Which of the following statements about reaction intermediates is correct?
They appear in the overall balanced equation
They are stable and long-lived species
They are formed and consumed during the reaction mechanism
They always increase the rate of reaction
In a reaction where the rate law is Rate = k[A]⁰, what happens to the rate if the concentration of A is doubled?
Doubles
Halves
Remains the same
Quadruples
The activation energy of a reaction is:
The energy difference between reactants and products
The minimum energy required for reactants to form products
The total energy released in the reaction
The energy of the catalyst
Which factor generally increases the rate constant k of a reaction?
Decreasing temperature
Increasing temperature
Increasing volume
Decreasing pressure
For a reaction with rate law Rate = k[A]², if the concentration of A is tripled, the rate will:
Increase by 3 times
Increase by 6 times
Increase by 9 times
Remain unchanged
The rate determining step is often:
The fastest step in the mechanism
The step with the lowest activation energy
The slowest step controlling the overall rate
The last step only
In a reaction where the rate is proportional to [A]¹[B]⁰, the overall order is:
The half-life of a zero order reaction is:
Independent of initial concentration
Directly proportional to initial concentration
Inversely proportional to initial concentration
Equal to the rate constant
Which of the following reactions is likely to be zero order?
Photochemical reactions
Radioactive decay
First order decomposition
Second order bimolecular reactions
For a reaction A → products, the rate law is Rate = k[A]ᵐ. If doubling [A] increases the rate by four times, the order m is:
Which of the following is true for the half-life of a first order reaction?
It decreases as the reaction proceeds
It depends on the initial concentration
It remains constant throughout the reaction
It increases with temperature
The rate constant k has units of s⁻¹ in which order of reaction?
Zero order
First order
Second order
Third order
Which of the following best describes a pseudo first order reaction?
Reaction rate depends on two reactants equally
One reactant is in large excess making the rate appear first order
The reaction is zero order overall
The reaction has no rate determining step
The rate of reaction is measured by:
Change in temperature per unit time
Change in concentration per unit time
Change in volume per unit time
Change in pressure per unit time
If a reaction has a rate constant k = 0.05 s⁻¹, what is the half-life of this first order reaction?
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