Tag: chemical kinetics

Questions Related to chemical kinetics

On increasing the temperature by $10^{0}$C:

chemistry chemical kinetics collision theory collision theory of chemical reactions rate of chemical reaction

  1. number of collisions get doubled

  2. value of rate constant does not change

  3. energy of activation increases

  4. number of fruitful collisions gets doubled

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Correct Option: D
Explanation:

Increasing the temperature of the substance, increases the fraction of molecules which collide with energies greater than $Ea$. For every $10^0 C$ rise in temperature, the fraction of molecules having energy equal to or greater than Ea gets doubled leading to doubling the rate of reaction.

Hence, the number of fruitful collisions gets doubled.

The time required to complete $\dfrac{3}{4}th$ of first order reaction is $32 min.$ then find $t _{\frac{1}{2}} = ?$

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. $16$

  2. $160$

  3. $1600$

  4. $32$

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Correct Option: A
Explanation:

$t _{\dfrac{3}{4}} = 2t _{\dfrac{1}{2}} = 32min.$
$t _{\dfrac{1}{2}} = 16min.$

The first order rate constant for dissociation of $N _2O _5$ is $6.2\times 10^{-4}s^{-1}$. The half-life period (in $s$) of this dissociation will be.

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. $1117.7$

  2. $111.7$

  3. $223.4$

  4. $160.9$

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Correct Option: A
Explanation:
$t _{1/2}=\displaystyle\frac{0.693}{k}$
$=\displaystyle\frac{0.693}{6.2\times 10^{-4}}=1117.7s$

For a first order reaction with half-life of $150$ second , the time taken for the concentration of the reactant to fall from $M/10$ to $M/100$ will be approximately 

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. $1500\ s$

  2. $500\ s$

  3. $900\ s$

  4. $600\ s$

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Correct Option: A

How many minutes will it take to plate out $5.0g$ of $Cr$ form a $Cr _2(SO _4) _3$ solution using a current of $1.50A$?

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. $254$

  2. $309$

  3. $152$

  4. $103$

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Correct Option: B

Which of the following is first order ?
i) Decomposition of $NH _{4}NO _{3}$ in aqueous solution.
ii) Inversion of cane sugar in the presence of an acid
iii) Base hydrolysis of ethyl acetate.
iv) All radioactive decays.
The correct combination is:

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. i, ii, iv

  2. All are correct

  3. ii, iv

  4. ii, iii, iv

Show answer
Correct Option: A
Explanation:

Base hydrolysis of ethyl acetate is a second order reaction.
The other reactions are first order reactions.

The acid hydrolysis of the ester is:
(i) first order reaction
(ii) bimolecular reaction
(iii) unimolecular reaction
(iv) second order reaction

The true statements are:

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. i, ii

  2. All are correct

  3. ii, iv

  4. ii, iii, iv

Show answer
Correct Option: A
Explanation:

$CH _{3}COOC _{2}H _{5}+H _{2}O\rightarrow CH _{3}COOH+C _{2}H _{5}OH$
$ rate=K[CH _{3}COO\ C _{2}H _{5}]^{1}[H _{2}O]^{0}$
thus, it is first order & bi molecular reaction.

Thus, statement i and ii are correct.

The hydrolysis of acetic anhydride$(CH _3CO) _2O+ H _2O\rightarrow2CH _3COOH$ is an example of :

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. Pseudo first order reaction

  2. Pseudo second order reaction

  3. Zero order reaction

  4. Third order reaction

Show answer
Correct Option: A
Explanation:

It is an example of pseudo first order reaction because here $H _{2}O$ is in excess. Thus, rate of reaction depends on only concentration of acetic anhydride.
So, rate is given by
$=k[(CH _{3}CO) _{2}O]$

For which of the following reactions the molecularity and orders of the reaction are two and two respectively:

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. ester hydrolysis in acid medium.

  2. inversion of cane sugar in acid aqueous solution.

  3. hydrolysis of ethyl acetate in caustic soda aqueous solution.

  4. decomposition hydrogen peroxide in acid solution.

Show answer
Correct Option: C
Explanation:

The hydrolysis of ethyl acetate in caustic soda aqueous solution is represented by the following reaction.
$CH _{3}COOC _{2}H _{5}+NaOH\rightarrow  CH _{3}COONa+C _{2}H _{5}OH$
The expression for the rate of the reaction is $r=k[CH _{3}COOC _{2}H _{5}][NaOH].$
The overall order of the reaction is 2 and it is a bimolecular reaction.

The rate constant, $\mathrm{k}$ for the reaction $\displaystyle \mathrm{N} _{2}\mathrm{O} _{5}(\mathrm{g})\rightarrow 2\mathrm{N}\mathrm{O} _{2}(\mathrm{g})+\frac{1}{2}\mathrm{O} _{2}(\mathrm{g})$ ls $2.3\times 10^{-2}\mathrm{s}^{-1}$. Which equation given below describes the change of $[\mathrm{N} _{2}\mathrm{O} _{5}]$ with time?

$[\mathrm{N} _{2}\mathrm{O} _{5}] _{0}$ and $[\mathrm{N} _{2}\mathrm{O} _{5}] _{\mathrm{t}}$ correspond to concentration of $\mathrm{N} _{2}\mathrm{O} _{5}$ initially and at time $\mathrm{t}$.

chemistry chemical kinetics kinetic study of some first order reactions rate of chemical reaction endothermic and exothermic reactions

  1. $[N _{2}O _{5}] _{t}=[N _{2}O _{5}] _{0}+kt$

  2. $[N _{2}O _{5}] _{0}=[N _{2}O _{5}] _{t}e^{kt}$

  3. $log _{10}[N _{2}O _{5}] _{t}=log _{10}[N _{2}O _{5}] _{0}-kt$

  4. $ln\dfrac{[N _{2}O _{5}] _{0}}{[N _{2}O _{5}] _{t}}=kt$

Show answer
Correct Option: D
Explanation:

The decomposition of  $\mathrm{N} _{2}\mathrm{O} _{5}$ follows first order kinetics.


The integrated rate law expression is $ln\dfrac{[N _{2}O _{5}] _{0}}{[N _{2}O _{5}] _{t}}=kt$.

It can also be represented as $log _{10}[N _{2}O _{5}] _{t}=log _{10}[N _{2}O _{5}] _{0}-\dfrac {kt} {2.303}.$


It can also be represented as $[N _{2}O _{5}] _{t}=[N _{2}O _{5}] _{0}e^{-kt}.$