Tag: chemical kinetics

Questions Related to chemical kinetics

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 $=$ ___.

chemistry chemical kinetics introduction to chemical kinetics understanding chemical kinetics rate of chemical 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, $\dfrac {a}{2k}, \dfrac {\triangle [A]}{\triangle t}, \dfrac {dx}{dt}$

Show answer
Correct Option: D
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 } $                    

Chemical kinetics a branch of physical chemistry deals with:

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

  1. structure of molecules

  2. heat changes in a reaction

  3. physical changes in a reaction

  4. rate of reactions

Show answer
Correct Option: D
Explanation:
Chemical kinetics is branch of physical chemistry that is concerned with understanding the rates of chemical reactions.

Structures and physical changes are deal in solid state and while studying liquids.

Thermochemistry deals with energy changes in chemical reactions.


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?

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

  1. $-RT\ ln2$

  2. $RT\ ln2$

  3. $2RT$

  4. $\dfrac {RT}{2}$

Show answer
Correct Option: A
Explanation:

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

Which of the following theory is not related to the chemical kinetics?

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

  1. Collision theory

  2. Absolute theory

  3. Absolute reaction rate

  4. VSEPR theory

Show answer
Correct Option: D
Explanation:

Valence shell electron pair repulsion (VSEPR) theory is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms.

It's not related to the chemical kinetics.

Chemical kinetics, a branch of physical chemistry, deals with:

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

  1. heat changes in a reaction

  2. physical changes in a reaction

  3. rate of reactions

  4. structure of molecules

Show answer
Correct Option: C
Explanation:

Chemical word is related to reaction and kinetics is related to speed or rate, hence in chemical kinetics we study rate of reaction.

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

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

  1. $K=10$

  2. $K=1$

  3. $K={ 10 }^{ 3 }$

  4. $K={ 10 }^{ -2 }$

Show answer
Correct Option: C
Explanation:

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

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

If the door of a refrigerator is kept open in a dosed room then room:

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

  1. heated

  2. cooled

  3. heated or cooled depending upon the initial temperature of the room

  4. neither cooled nor heated

Show answer
Correct Option: A
Explanation:

When the action of fridge is running, it takes air inside the fridge and cools it by removing heat from it and this heat come out from the back of fridge by a little fan. More heat comes outside the fridge. So if you even open the fridge door the cool air escape the fridge will heats up the room more ten cooling.  

Find out the correct order of rate of reaction towards allylic substitution :
(I) $CH _3 - CH = CH _2$
(II) $CH _3 -CH _2 - CH = CH _2$
(III) $CH _3 - \overset{CH _3}{\overset{\!\!\!\!\!\!|}{CH}} - CH = CH _2$
chemistry chemical kinetics introduction to chemical kinetics understanding chemical kinetics rate of chemical reaction

  1. ${\rm{I}}\,\,{\rm{ > }}\,\,{\rm{II}}\,\,{\rm{ > }}\,\,{\rm{III}}$

  2. ${\rm{II}}\,\,{\rm{ > }}\,\,{\rm{I}}\,\,{\rm{ > }}\,\,{\rm{III}}$

  3. ${\rm{III}}\,\,{\rm{ > }}\,\,{\rm{I}}\,\,{\rm{ > }}\,\,{\rm{II}}$

  4. ${\rm{III}}\,\,{\rm{ > }}\,\,{\rm{II}}\,\,{\rm{ > }}\,\,{\rm{I}}$

Show answer
Correct Option: B

A chemist puts a sample of dilute aqueous hydrochloric acid into beaker $1$. She adds a sample of zinc and measures the rate of production of hydrogen gas.
She then puts a different sample of dilute aqueous hydrochloric acid into beaker $2$. She adds a different sample of zinc and measure the rate of production of hydrogen gas.
The rate of the reaction in beaker $2$ is greater than the rate of the reaction in beaker $1$.
Which factors could help to explain this observation?
$1$. The reaction in beaker $1$ has a higher activation energy than the reaction in beaker $2$.
$2$. The zinc in beaker $1$ is in larger pieces than the zinc in beaker $2$.
$3$. The acid in beaker $1$ is at a lower concentration than the acid in beaker $2$.

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

  1. $1, 2$ and $3$ are correct

  2. $1$ and $2$ only are correct

  3. $2$ and $3$ only are correct

  4. $1$ only is correct

Show answer
Correct Option: C
Explanation:
Since the rate of reaction in beaker $2$ is greater than the rate of reaction in beaker $1$, thus the concentration of acid in beaker $2$ will be greater than that in beaker $1$.
Also, lower the activation energy, the faster the rate of reaction. Thus the reaction in beaker $2$ has a lower activation energy than the reaction in beaker $2$.
Also the zinc in beaker $2$ will be in small pieces than that in beaker $2$ as large pieces will break slowly to react.
Hence $1, \; 2$ and $3$ are correct.

The approach to the following equilibrium was observed kinetically from both directions:
$ Pt{ Cl } _{ 4 }^{ -2 }+H _{ 2 }O\rightleftharpoons Pt(H _{ 2 }O)CI _{ 3 }+Cl^{ - } $
At $ 25^o C,$  it was found that  $ -\dfrac { d[PtC{ l } _{ 4 }^{ 2- }] }{ dt } =(3.9  \times 10^{ -5 } s^{ -1 }) [PtC{ l } _{ 4 }^{ 2- }]-(2.1  \times 10^{ -3 } L mol^{ -1 }s^{ -1 }) [Pt(H _{ 2 }O)C{ l } _{ 3 }^{ - }][Cl^{ - }] $
The value of $ K _{eq} $ (equilibrium constant) for the complexation of the fourth $ cl^- $ by $ Pt( II ) $ is

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

  1. $ 53.8 mol L^{-1} $

  2. $ 0.018 mol L^{-1} $

  3. $ 53.8 L mol^{-1} $

  4. $ 0.018 L mol^{-1} $

Show answer
Correct Option: A