Tag: chemical kinetics

Questions Related to chemical kinetics

The rate of certain hypothetical reaction A + B + C $\rightarrow$ Products, is given by $\displaystyle r\, =\, - \frac{dA}{dt}\, = k[A]^{1/2}[B]^{1/3}[C]^{1/4}$ The order of a reaction is given by:

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

  1. $1$

  2. $\displaystyle \frac{1}{2}$

  3. $2$

  4. $\displaystyle \frac{13}{12}$

Show answer
Correct Option: D
Explanation:

$A + B + C$ $\rightarrow$ Products
$\displaystyle r\, =\, - \frac{dA}{dt}\, = k[A]^{1/2}[B]^{1/3}[C]^{1/4}$
so order is
$\displaystyle \frac{1}{2}\, +\, \frac{1}{3}\, +\, \frac{1}{4}\, =\,\frac{13}{12}$

Consider the following elementary reaction,
    $2A + B + C \rightarrow Products$.
All reactant are present in the gaseous state and reactant C is taken in excess.

What is the unit of rate constant of the reaction?

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

  1. $mol\, L^{-1}\, time^{-1}$

  2. $time^{-1}$

  3. $mol^{-1}\, L^{2}\, time^{-1}$

  4. $mol^{-2} L^{2} time^{-1}$

Show answer
Correct Option: D
Explanation:

Since C is taken in excess, so its concentration does not change. So it is not taken in rate expression of the reaction.


and rate law is given by,

$Rate = k[A]^{2}[B]$

Order of the reaction $= 3$

 For the third-order reaction, the unit of the rate constant is given by -

      $= [conc.]^{1 - n} {time}^{-1}= [conc.]^{1 - 3} {time}^{-1}=\, mol^{-2} L^{2} time^{-1}$

The second order rate constant is usually expressed as:

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

  1. Mol L $s^{-1}$

  2. $Mol^{-1}\, L^{-1}\, s^{-1}$

  3. $Mol\, L^{-1}\, s^{-1}$

  4. $Mol^{-1}\, L\, s^{-1}$

Show answer
Correct Option: D
Explanation:

As we know,
for second order reaction:
$r = k[A]^2$
so unit of rate constant is $Mol^{-1}\, L\, s^{-1}$.

For a reaction having order equal to $3/2$, the units for rate constant are ${ sec }^{ -1 }$.
chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Rate $r = k[A]^{3/2}$

Unit of rate constant $k = [A]^{1-3/2}[time]^{-1}$
$k = [A]^{-1/2}[time]^{-1}$

The rate of certain hypothetical reaction $A+B+C\rightarrow $ products is given by, $\displaystyle r=-\frac{\mathrm{d} [A]}{\mathrm{d} t}=K[A]^{1/2}:K[B]^{1/3}:K[C]^{1/4}$. The order of the reaction:

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

  1. 1

  2. $\displaystyle \frac{1}{2}$

  3. 2

  4. $\displaystyle \frac{13}{12}$

Show answer
Correct Option: D
Explanation:

$r=-\dfrac { d[A] }{ dt } =K[A{ ] }^{ \cfrac { 1 }{ 2 }  }K[B{ ] }^{ \cfrac { 1 }{ 3 }  }K[C{ ] }^{ \cfrac { 1 }{ 4 }  }\ $


$rate=\dfrac { 1 }{ 2 } +\dfrac { 1 }{ 3 } +\dfrac { 1 }{ 4 } \ $

$rate=\dfrac { 13 }{ 12 }$

Hence, the answer is D.

The rate constant of third order reaction is:

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

  1. mol lit$^{-1}$ s$^{-1}$

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

  3. mol$^{-1}$ lit s$^{-1}$

  4. mol$^{-2}$ lit$^{-1}$ s$^{-1}$

Show answer
Correct Option: B
Explanation:

Units of rate constant for $n$th order = $[(mol\  lit^{-1})]^{1-n} t^{-1}$
For third order reaction $n = 3$
$\therefore $ Units are $(mol  lit^{-1})^{1- 3} t^{-1} = mol\ l^{-2} lit^{-2} t^{-1}$

The rate constant of a reaction depends on:

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

  1. Temperature

  2. Initial concentration ofthe reaction

  3. Time ofreaction

  4. Extent of reaction

Show answer
Correct Option: A
Explanation:

The rate constant of a reaction depends only on two factors
(i) Temperature and (ii) Catalyst.

The rate constant of a first-order reaction is $3 \times 10^{-6}$ per second and initial concentration is 0.10 M. Then the initial rate of reaction is:

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

  1. $3 \times 10^{-6} Ms^{-1}$

  2. $3 \times 10^{-8} Ms^{-1}$

  3. $3 \times 10^{-7} Ms^{-1}$

  4. $3 \times 10^{-9} Ms^{-1}$

Show answer
Correct Option: C
Explanation:

Rate = k [concentration] for first order reaction.
Given $k = 3 \times 10^{-6}/sec,$ [concentration] = 0.1 M
$\therefore rate = 3 \times 10^{-6} \times 0.1  = 3 \times 10^{-7} ms^{-1}$

What is the unit for the rate constant of 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. $\displaystyle { s }^{ -1 }$

  2. mol $\displaystyle { L }^{ -1 }$

  3. mol $\displaystyle { L }^{ -1 }{ s }^{ -1 }$

  4. L $\displaystyle { mol }^{ -1 }{ s }^{ -1 }$

  5. $\displaystyle { mol }^{ 2 }{ L }^{ -2 }{ s }^{ -2 }$

Show answer
Correct Option: D
Explanation:

The unit for the rate constant of a second order reaction is $\displaystyle \displaystyle L { mol }^{ -1 }{ s }^{ -1 } $. 
For a second order reaction, $\displaystyle rate = k [A]^2 $
$\displaystyle mol { L }^{ -1 }{ s }^{ -1 }  = k (mol { L }^{ -1 })^2$
$\displaystyle k = L { mol }^{ -1 }{ s }^{ -1 }  $

Statement I : In a second order reaction doubling [A] quadruples the rate
Because
Statement II : The rate equation is $\displaystyle r={ k\left[ A \right]  }^{ 2 }$ for such a reaction

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

  1. Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1 .

  2. Both the Statement 1 and Statement 2 are correct and Statement 2 is not the correct explanation of Statement 1.

  3. Statement 1 is correct but Statement 2 is not correct.

  4. Statement 1 is not correct but Statement 2 is correct.

  5. Both the Statement 1 and Statement 2 are not correct.

Show answer
Correct Option: A
Explanation:

Secon order rate expression is given as $r$$=$$k[A]^2$ so if we double the concentration of a then rate increases by 4 times, hence both statements are correct and statement 2 is correct explanation of statement 1.