Tag: chemical kinetics

Quizzes (10) Questions (179)

Questions Related to chemical kinetics

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

What does the exponential factor represent?

  1. The total number of reactants in a reaction.

  2. The amount of energy needed to start a chemical reaction.

  3. The fraction of reactants that have approached the activation energy hill and made it over per number of attempts.

  4. The fraction of reaction energy given off per unit of time.

  5. The fraction of products that have approached the activation energy hill and made it over per number of attempts.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The exponential factor represents the fraction of "reactants" that have approached the activation energy hill and made it over per number of attempts.

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

In a reaction mechanism consisting of elementary reaction steps where the relative rate of each is given, which of the following is most likely to be the rate-determining step?

  1. A step labeled fast

  2. A step labeled moderate

  3. A step labeled slow

  4. It is not possible to tell which step is rate determining from this information.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In a multi-step reaction, the elementary step having the slowest-rate is always the rate determining step of the overall reaction.

Therefore, a step labeled slow will be the rate determining step.

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

Statement: The rate of instantaneous reactions can be determined experimentally.


State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Instantaneous rate: It can be determined graphically by using the concentrations of reactant or product at different time intervals.


Hence, the given statement is $\text{true}$

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

Rate of formation of ${ SO } _{ 3 }$ according to the reaction $2{ SO } _{ 2 }+O _{ 2 }\rightarrow 2{ SO } _{ 3 }\quad is\quad 1.6\times { 10 }^{ -3 }kg\quad min^{ -1 }$. Hence rate at which $SO _{ 2 }$ reacts is:

  1. $1.6\times { 10 }^{ -3 }kg\quad { min }^{ -1 }$
  2. $8.0\times { 10 }^{ -4 }kg\quad { min }^{ -1 }$
  3. $3.2\times { 10 }^{ -3 }kg\quad { min }^{ -1 }$
  4. $1.28\times { 10 }^{ -3 }kg\quad { min }^{ -1 }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$2 SO _2 + O _2 \rightleftharpoons  2 SO _3$


$\dfrac{1}{2}\dfrac{d[SO _3]}{dt} = 1.6 \times 10^{-3} kg/min = \dfrac{1.6 \times 10^{-3}}{80} mol/min$                             $[\because M _{SO _3}= 80 \times 10^{-3} Kg/mol]$


$\dfrac{-1}{2}\dfrac{d[SO _2]}{dt} = \dfrac{+1}{2}\dfrac{d[SO _3]}{dt}$

$= -\dfrac{1.6 \times 10^{-3}}{80 \times 10} $ mol/min

$= -\dfrac{1}{50} \times 64 \times 10^{-3} = -1.28 \times 10^{-3} $ kg/min

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

For a reaction
$2A+B\rightarrow C+D$, the active mass of $B$ is kept constant but that of $A$ is tripled. The rate of reaction will -

  1. Decrease by $3$ times
  2. Increased by $9$ times
  3. Increase by $3$ times

  4. Unpredictable
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the given reaction, $ Rate = k[A]^{2}[B]^{1} $

When A becomes 3A i.e. triples, the rate will become: $ Rate^{'} = k[3A]^{2}[B]^{1} = 9k[A]^{2}[B] $
Thus, rate of reaction is increased by 9 times. 

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

The study of chemical kinetics becomes highly complicate if there occurs:

  1. reversible reaction

  2. side reaction

  3. surface reaction

  4. none of these
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

The study of chemical kinetics becomes highly complicate if there occurs side reactions or surface reactions.These reactions bring changes in the value of rate constant and not help to proceeds the reaction in the right manner.

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

The container of $2$ litrer contains $4$ mole of $N _{2}O _{5}$. On heating to $100^{\circ}C, N _{2}O _{5}$ undergoes complete dissociation to $NO _{2}$ and $O _{2}$. Select the correct answers if rate constant for decomposition of $N _{2}O _{5}$ is $6.2\times 10^{-4}sec^{-1}$.
1. The mole ratio before and after dissociation is $4 : 2$
2. Half life of $N _{2}O _{5}$ is $1117\ sec$ and it is independent of concentration.
3. Time required to complete $40$% of reaction is $824\ sec$.
4. If volume of container is doubled, the initial rate of decomposition becomes half of the initial rate.

  1. $1, 3, 4$
  2. $1, 2, 3, 4$
  3. $3, 4$
  4. $2, 3, 4$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Because reaction is first order

$\vartheta =k[A]$
$A=A _{0}e^{-kt}$

for which

$t _{40}=824$sec
if$v _{f}=2V _{i}\Rightarrow C _{f}=\frac{C _{i}}{2}\Rightarrow \vartheta _{f}=\frac{\vartheta _{i}}{2}$

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

In pseudo unimolecule reactions:

  1. both the reactants are present in low concentration

  2. Both the reactants are present in same concentration

  3. One of the reactant is present in excess

  4. One of the reactant is non-reactive
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Pseudo Unimolecular Reaction. The reactions having molecularity two but the order of reaction is one is called pseudo unimolecular reactions,in such type of reactions, one reagent is take in the excess amount so that the disappearance of that reagent is negligible and it does not determine the rate of reaction.

Example:
  • Hydrolysis of ester$CH _3COOC _2H _5$,
  • Hydrolysis of sucrose.

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

The value of rate of a pseudo first order reaction depends upon:

  1. the concentration of both the reactants present in the reaction

  2. the concentration of the reactant present in small amount

  3. the concentration of the reactant present in excess
  4. the value of $\Delta H$ of the reaction
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$CH _3COOC _2H _5 + H _2O \rightarrow CH _3COOH + CH _3OH$
          0.01                    10                   0                      0

            0                      9.99              0.01               0.01 

The above reaction is a Pseudo first order reaction. As it can be seen from the above reaction that the concentration of water is not changing much. Thus the rate of the reaction is not much affacted by the change in concentration of  water. However rate of the reaction get significantly affacted by the concentration gradient of ethyl acetate. Hence, the rate of Pseudo first order reaction depends upon the concentration of the reactant present in small amount.

Option B is correct.