Tag: dependence of reaction rate on concentration of reactants

Questions Related to dependence of reaction rate on concentration of reactants

For the second order reaction, if the concentration of reactant changes from $0.08M$ to $0.04M$ in 10 minutes. Calculate the time at which concentration of reactant becomes $0.01M$.

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. $20min$

  2. $30min$

  3. $50min$

  4. $70min$

Show answer
Correct Option: D
Explanation:

For a second order reaction we have 

$ \cfrac { 1 }{ { [A] } _{ t } } -\cfrac { 1 }{ [A] _{ o } } =kt$
 In $10$ minutes,  concentration changes from $0.08M $ to $0.04M$
$ \left( \cfrac { 1 }{ 0.04 } -\cfrac { 1 }{ 0.08 }  \right) \cfrac { 1 }{ 10 } =k{ \quad min }^{ -1 }\ 1.25{ min }^{ -1 }=k$ 
Substituting value of $k$, we get it become $ \left( \cfrac { 1 }{ 0.01 } -\cfrac { 1 }{ 0.08 }  \right) \cfrac { 1 }{ 1.25 } =t\ 70min=t$
 Hence answer is $[D]$

For a second order reaction rate at a particular time is $x$. Ifthe initial concentration is trapled, the rate will becomes?

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. $3x$

  2. $9x^{2}$

  3. $9x$

  4. $27x$

Show answer
Correct Option: C
Explanation:

Its a second Order reaction.


The rate at a particular time is x. 

$x = k{[A]}^{2}$

If the initial concentration is tripled, the rate becomes

$rate = k[{3[A]}^{2}]$ = $9x$

The given reaction 
$2FeCl _{3}+SnCl _{2}\rightarrow 2FeCl _{2}+SnCl _{4}$
Is an example of:

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. Third order reaction

  2. First order reaction

  3. Second order reaction

  4. None of these

Show answer
Correct Option: A
Explanation:

For the third order reaction, the general reaction can be written as,

$A+B+C\rightarrow Products\ r={ K } _{ 3 }\left[ A \right] ^{ 2 }\left[ B \right] ^{ 1 }$
$r=\left[ Fe{ Cl } _{ 2 } \right] ^{ 2 }\left[ Sn{ Cl } _{ 4 } \right] ^{ 1 }$
the order of products are third order.

The rate constant for forward and backward reaction of hydrolysis of ester are $1.1\times 10^{-2}$ and $1.5\times 10^{-3}$ per minute respectively.  


Equilibrium constant for the reaction is :


$CH _3COOC _2H _5 + H _2O\    \rightleftharpoons\ CH _3COOH+C _2H _5OH$ 

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. 4.33

  2. 5.33

  3. 6.33

  4. 7.33

Show answer
Correct Option: D
Explanation:

Rate constant of forward reaction $(K _f)=1.1\times 10^{-2}\ min^{-1}$

Rate constant of backward reaction $(K _b)=1.5\times 10^{-3}\ min^{-1}$ 
Equilibrium constant $(K _c)$$=\dfrac {K _f}{K _b}$

$=\dfrac {1.1\times 10^{-2}}{1.5\times 10^{-3}}$

$=7.33$
Hence, option $(D)$ is correct.

The dimensions of rate constant of a second order reaction involves:

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. neither time nor concentration

  2. only time

  3. time and concentration

  4. time square and concentration

Show answer
Correct Option: C
Explanation:

second order
$2A \rightarrow product$
$rate=K[A]^{2}$
$k=\frac{rate}{[A]^{2}}$
$=\frac{concentration}{time (concentration )^{2}}$
$=\frac{1}{time . concentration}$
So it involves both time & concentration.

Except for first ofder reactions, the unit of rate constant depends on the dimensions
($mol^{1-n}.lit^{-1}.sec^{-1}  $) concentration and time.
Where, n= order of the reaction.


Which is not true for a second order reaction ?

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. It can have rate constant $1 \times 10^{-2} $ $L mol^{-1} s^{-1} $

  2. Its half - life is inversely propotional to its initial concentration

  3. Time to compelete $75 % $ reaction is twice of half - life

  4. $ T _{50} $ = $ \frac { 1 }{ K\quad \times \quad Initial\quad conc. } $

Show answer
Correct Option: C
Explanation:

Unit of Rate Constant for a second order reaction is ${mol}^{-1}L{s}^{-1}$.


${t} _{1/2}\space \alpha\space {a}^{1-n}$. Here n =2 

${t} _{1/2}\space \alpha\space {a}^{-1}$. So Its Inversely Proportional to Half Life.

${t} _{1/2}$ = $\dfrac{1}{ak}$ where a is initial concentration

TIme to complete 75% reaction is twice to half life is false. Its is true for 1st Order Reaction

For a second order reaction rate at a particular time is $X$. If the initial concentration is tripled, the rate will become:

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. $3X$

  2. $9X^2$

  3. $9X$

  4. $27X$

Show answer
Correct Option: B
Explanation:

Its a second Order Reaction. Rate is given as X

$\therefore rate=[x]^2$
When the concentration is tripled then,
$rate=[3x]^2=9x^2$

Which of the following statements is incorrect?

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. A second order reaction must be a bimolecular elementary reaction

  2. A bimolecular elementary reaction must be a second order reaction

  3. Zero order reaction must be a complex reaction

  4. First order reaction may be complex or elementary reaction.

Show answer
Correct Option: B
Explanation:

A bimolecular elementary reaction may or may not be a Second Order Reaction whereas a Second Order reaction must be a bimolecular elementary reaction.

Ex: Decomposition of ${N} _{2}O _{5}$ is a 1st Order Reaction though its a bimolecular reaction.

The rate of solvolysis of tert-butyl bromide will be maximum in which of the following solvents?

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. ${ Et } _{ 2 }O$

  2. ${CCl} _{4}$

  3. $EtOH$

  4. ${H} _{2}O$

Show answer
Correct Option: D
Explanation:

The rate of solvolysis of Tert - butyl bromide will be maximum in Water.

tert-butyl bromide follows $SN1$ mechanism thus it prefers weak nucleophiles like water.

The inversion of cane sugar to produce glucose and fructose is represented by the reaction
     ${ C } _{ 12 }{ H } _{ 22 }{ O } _{ 11 }+{ H } _{ 2 }O\quad \xrightarrow { { H }^{ + } } { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 }+{ C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 }$
The reaction is:

chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. second order

  2. unimolecular

  3. pseudo uni-molecular

  4. bi molecular

Show answer
Correct Option: C
Explanation:

Inversion of Cane Sugar to produce glucose and fructose is a Pseudo uni-molecular Reaction.

Here the rate of reaction is made first order by changing the concentration of sucrose ($C _{12}H _{22}O _{11}$).