Chemistry

Chemical Kinetics

256 Questions

Chemical kinetics involves the study of chemical reaction rates and the factors affecting them, such as temperature and concentration. This topic covers rate laws, half-life, and zero, first, and second order reactions. It is a crucial part of the chemistry syllabus for various competitive examinations.

Reaction rate parametersFirst order kineticsZero and second orderHalf-life of reactionRate constant units

Chemical Kinetics Questions

Multiple choice

Which of the following statements is correct concerning Michales constant Km?

  1. It is measured in the same units as the rate of the enzyme-catalysed reaction.

  2. It varies with the amount of enzyme used in measuring the reaction rate.

  3. It can be considered to be a measure of affinity of an enzyme for its substrate.

  4. It has a low value to indicate a low affinity for the substrate.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The concentration of substrate when the velocity of the reaction is half of the maximum velocity is expressed as Michales Menten constant Km. The lower the value of Km, the greater the affinity of enzymes for the substrate.

Multiple choice

Which of the following values of rate constants indicate zero order reaction?

  1. 4.25 x 10-3 sec-1 2. 4.25 x 10-2 mole L-1 sec-1 3. 9.2 x 10-6 mole L-1 sec-1 4. 6.04 x 10-5 sec-1 5. 4.3 x 10-6 L mol-1 sec-1 Select the correct answer using codes given below:

  1. 1 and 2 only

  2. 1 and 4 only

  3. 2 and 3 only

  4. 2 and 4 only

  5. 3 and 5 only
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

4.25 x 10-2 mole L-1 sec-1 - Zero order reaction 9.2 x 10-6 mole L-1 sec-1- Zero order reaction

Multiple choice

Which of the following statements is true about SN1 reaction mechanism?

  1. Fast step is rate determining step.

  2. It is second order reaction.

  3. It is associative mechanism.

  4. It is unimolecular reaction.

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This option is correct because in SN1 mechanism, the single reacting complex ions substitute the ligand due to metal ligand breaking to form five coordinated intermediate complex.

Multiple choice

The half life of a zero order reaction, A --> Products is:

  1. directly proportional to the initial concentration

  2. directly proportional to the initial rate constant

  3. independent of the initial concentration

  4. inversely proportional to the initial concentration
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For a zero order reaction, A --> Products is inversely proportional to the rate constant.

Multiple choice

Directions: The study about reaction rate and their changes depending on the changes in experimental parameters such as temperature, concentration of substrate and pH is known as enzyme kinetics.

What is the significance of Kcat/Km ratio?

  1. Denotes the constant for ES formation

  2. Denotes Michaelis constant

  3. Denotes specificity constant

  4. Denotes turn-over number

  5. Denotes the constant for ES disappearance
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The ratio Kcat/Km is similar to the rate constant of the reaction between substrate and the enzyme. Kcat/Km is known as the specificity constant which signifies the efficiency of an enzyme.

Multiple choice

Directions: The study about reaction rate and their changes depending on the changes in experimental parameters, such as temperature, concentration of substrate and pH is known as enzyme kinetics.

Michaelis-Menten equation related to steady state kinetics is given by

  1. υ0 = υmax [S]/ (Km + [S])

  2. [S]/υ0 = [S]/υmax + Km/ υmax<o:p></o:p>

  3. Kcat = υmax/ Et<o:p></o:p>

  4. υ0/ [S] = - υ0/ Km + υmax/ Km

  5. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Michaelis-Menten equation related to steady-state kinetics is given by

υ0 = υmax [S]/ (Km + [S]) where υ0 is the initial reaction rate, υmax is the maximum reaction rate, [S] is the substrate concentration and Km is Michaelis Constant.

Multiple choice

Which of the following values of rate constants indicates first order reaction? i. 3.2 x 10-3 sec-1 ii. 4.25 x 10-2 mol L-1 s-1 iii. 8.1 x 10-6 mol L-1 s-1 iv. 4.06 x 10-5 s-1 v. 3.9 x 10-6 L mol-1 s-1 Select the correct answer using codes given below:

  1. i and ii

  2. i and iv

  3. ii and iii

  4. ii and iv

  5. iii and v
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For first order reaction, the rate constant has units of s−1. 3.2 x 10-3 s-1: First order reaction. 4.06 x 10-5 s-1: First order reaction.

Multiple choice

In the reaction aA + bB +cC → products, following observations are made. I - if concentration of A is doubled, keeping the concentration of B and C constant, the rate of reaction becomes double. II - if the concentration of B is halved, keeping the concentration of A and C constant the rate of reaction remains unaffected. III - If concentration of C is made 1.5 times, the rate of reaction becomes 2.25 times. The order of reaction is

  1. 1

  2. 2.5

  3. 3

  4. 3.5
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The answer can be calculated as follows: From observation 1, we observe that reaction is 1st order with respect to A. From observation 2, we observe,that reaction is zero order with respect to B. From observation 3, we observe that reaction is 2nd order with respect to C.Hence in total the reaction is of 3rd order.

Multiple choice

A zero order reaction means

  1. the rate of reaction is independent of the concentration of reactants

  2. the rate of reaction is independent of the concentration of the products

  3. the rate of reaction is independent of the concentration of reactants and products

  4. the rate the reaction is equal to the concentration of products divided by that of the reactants
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

ANS 1.