Chemistry

Chemical Kinetics

276 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

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.

Multiple choice

Biotransformation of an organic compound having concentration (x) can be modelled using an ordinary differential equation $\frac{dx}{dt} + kx^2 = 0$, where k is the reaction rate constant. If x = a at t = 0, then the solution of the equation is

  1. x = ae-kt
  2. $\frac{1}{x} = \frac{1}{a} + kt$

  3. x = a (1 - e-kt)

  4. x = a + kt
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

dx/dt = -kx^2. Separating variables: dx/x^2 = -k*dt. Integrating both sides: -1/x = -kt + C. At t=0, x=a, so -1/a = C. Thus, -1/x = -kt - 1/a, which simplifies to 1/x = 1/a + kt.

Multiple choice

In an actively growing (exponential phase) yeast culture, the cell concentration increased from 103 cells per ml to 107 cells per ml in 4 h. The doubling time of the yeast is

  1. 120 minutes

  2. 30 minutes

  3. 18 minutes

  4. 60 minutes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

During exponential growth, cell concentration follows N = N0 times 2^(t/td). Here, 10^7 equals 10^3 times 2^(4/td), which means 10^4 equals 2^(4/td). Taking logarithms and solving for td gives 4 hours divided by (4 times log2(10)), resulting in 18 minutes.

Multiple choice

An enzyme has a Km of 4.7 $\times$ 10–5 M and Vm is 22 micro moles per litre per min. The enzyme reaction is carried out at a substrate concentration of 2 $\times$ 10-4 M. The initial reaction velocity for this enzyme catalyzed reaction will be

  1. 6.5 micro moles per litre per min

  2. 17.8 micro moles per litre per min

  3. 13.0 micro moles per litre per min

  4. 8.9 micro moles per litre per min
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The Michaelis Menten equation is v = (Vm times S) / (Km + S). Substituting Vm = 22, Km = 4.7 times 10^-5, and S = 2 times 10^-4 into the formula yields an initial velocity of approximately 17.8 micro moles per litre per min.

Multiple choice chemistry chemical kinetics introduction to chemical kinetics understanding chemical kinetics rate of chemical reaction

Fill up the following with suitable terms.

(i) Activation energy $=$ Threshold energy $-$ ____.

(ii) Half-life period of zero order reaction $=$ __.

(iii) Average rate of reaction $=$ _.

(iv) Instantaneous rate of reaction $=$ ___.

  1. Potential energy, $\dfrac {0.693}{k}, \dfrac {dx}{dt}, \dfrac {\triangle [A]}{\triangle t}$
  2. Energy of reactants, $\dfrac {1}{k}, \dfrac {\triangle [A]}{\triangle t}, \dfrac {dx}{dt}$
  3. Energy of reaction, $\dfrac {\log k}{t}, \dfrac {\triangle [A]}{\triangle t}, \dfrac {dx}{dt}$
  4. Average kinetic energy of reactants, $\dfrac {a}{2k}, \dfrac {\triangle [A]}{\triangle t}, \dfrac {dx}{dt}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
a) Activation energy = Threshold energy$-$ the Average kinetic energy of molecules(by definition)

b) half-life of a zero order reaction = ${ t } _{ \frac { 1 }{ 2 }  } =\frac { a }{ 2k } $

c) Average rate of reaction = $\dfrac {\displaystyle \text{ Total change concentration reactants }}{ \displaystyle \text{Total time taken} }$  = $\dfrac { \triangle \left[ A \right]  }{ \triangle t }$

d) Instantaneous rate of reaction =$ \dfrac { \displaystyle \text {Instantaneous change in concentration} }{\displaystyle \text { Instantaneous  time} } $=$\dfrac { dx }{ dt } $                    
Multiple choice chemistry chemical kinetics introduction to chemical kinetics understanding chemical kinetics rate of chemical reaction

If reaction A and B are given with Same temperature and same concentration but rate of $A$ is double than $B$. Pre exponential factor is same for both the reaction then difference in activation energy $E _{A} - E _{B}$ is?

  1. $-RT\ ln2$
  2. $RT\ ln2$
  3. $2RT$
  4. $\dfrac {RT}{2}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\dfrac {r _{A}}{r _{B}} = \dfrac {A _{1}e^{\dfrac {-E _{A}}{RT}}}{A _{2}e^{\dfrac {-E _{B}}{RT}}}$
$\dfrac {2}{1} = \dfrac {e^{\dfrac {-E _{A}}{RT}}}{e^{\dfrac {-E _{B}}{RT}}}$
$ln2 = E _{B} - E _{A} / RT$
$E _{B} - E _{A} = RT\ ln2$
$E _{A} - E _{B} = -RT\ ln2$.

Multiple choice chemistry chemical kinetics introduction to chemical kinetics understanding chemical kinetics rate of chemical reaction

The rate of chemical reaction is directly proportional to the equilibrium constant.
In which of the following process reaction will be completed first?

  1. $K=10$
  2. $K=1$
  3. $K={ 10 }^{ 3 }$
  4. $K={ 10 }^{ -2 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The rate of chemical reaction is directly proportional to the equilibrium constant.

$\therefore $ For $K={ 10 }^{ 3 }$, the reaction will complete fastest.