Tag: understanding chemical kinetics

Quizzes (0) Questions (19)

Questions Related to understanding chemical kinetics

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

Chemical kinetics a branch of physical chemistry deals with:

  1. structure of molecules

  2. heat changes in a reaction

  3. physical changes in a reaction

  4. rate of reactions
Reveal answer Fill a bubble to check yourself
D Correct answer
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.


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

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

  1. Collision theory

  2. Absolute theory

  3. Absolute reaction rate

  4. VSEPR theory
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. heat changes in a reaction

  2. physical changes in a reaction

  3. rate of reactions

  4. structure of molecules
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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.

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

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

  1. heated

  2. cooled

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

  4. neither cooled nor heated
Reveal answer Fill a bubble to check yourself
A Correct answer
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.  

Multiple choice chemistry chemical kinetics introduction to chemical kinetics understanding chemical kinetics rate of chemical reaction
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) $CH _3 - \overset{CH _3}{\overset{\!\!\!\!\!\!|}{CH}} - CH = CH _2$
  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. ${\rm{III}}\,\,{\rm{ > }}\,\,{\rm{II}}\,\,{\rm{ > }}\,\,{\rm{I}}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Allylic substitution proceeds via free radical formation, and stability follows tertiary > secondary > primary free radicals. Structure III has a tertiary allylic hydrogen, structure II has a secondary one, and structure I has a primary one. Thus, the rate of reaction is highest for III and lowest for I.

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

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 $2$.

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice chemistry chemical kinetics introduction to chemical kinetics understanding chemical kinetics rate of chemical reaction

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

  1. $ 53.8 mol L^{-1} $
  2. $ 0.018 mol L^{-1} $
  3. $ 53.8 L mol^{-1} $
  4. $ 0.018 L mol^{-1} $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

At equilibrium, the rate of the forward reaction equals the rate of the backward reaction. Setting the two rate expressions equal: (3.9e-5)[PtCl4^2-] = (2.1e-3)[Pt(H2O)Cl3^-][Cl^-]. The equilibrium constant Keq = [Pt(H2O)Cl3^-][Cl^-] / [PtCl4^2-] = 3.9e-5 / 2.1e-3 = 0.01857. The question asks for the complexation of the fourth Cl-, which is the reverse of the given reaction, so K = 1/0.01857 = 53.8.