Tag: chemistry

Questions Related to chemistry

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

Which statements are correct in terms of chemical kinetic stuides?

chemistry chemical reactions and equations introduction to chemical kinetics understanding chemical kinetics rate of chemical reaction

  1. The quenching of a reaction can be made by cooling the reaction mixture.

  2. The quenching of a reaction can be made by diluting the reaction mixture.

  3. The reaction is supposed to be completed if it is kept for long time or strongly heated.

  4. None of the above

Show answer
Correct Option: A,B,C
Explanation:

The quenching of a reaction can be made by cooling as well as diluting the reaction mixture. The reaction is supposed to be completed if it is kept for a long time or strongly heated. Quenching a reaction is used to deactivate any unreacted reagents. It is also done by adding an antisolvent to induce precipitation, and collecting or removing the solids.

What does the exponential factor represent?

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

  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.

Show answer
Correct Option: C
Explanation:

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

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?

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

  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.

Show answer
Correct Option: C
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.

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


State whether the given statement is true or false.

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

  1. True

  2. False

Show answer
Correct Option: A
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 $\text{true}$