Tag: chemical kinetics

Quizzes (10) Questions (179)

Questions Related to chemical kinetics

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

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:

  1. $1$
  2. $\displaystyle \frac{1}{2}$
  3. $2$
  4. $\displaystyle \frac{13}{12}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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?

  1. $mol\, L^{-1}\, time^{-1}$
  2. $time^{-1}$
  3. $mol^{-1}\, L^{2}\, time^{-1}$
  4. $mol^{-2} L^{2} time^{-1}$
Reveal answer Fill a bubble to check yourself
D Correct answer
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 -

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

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

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:

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

  3. 2
  4. $\displaystyle \frac{13}{12}$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

The rate constant of third order reaction is:

  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$^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $(mol  lit^{-1})^{1- 3} t^{-1} = mol\ l^{-2} lit^{-2} t^{-1}$

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

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:

  1. $3 \times 10^{-6} Ms^{-1}$
  2. $3 \times 10^{-8} Ms^{-1}$
  3. $3 \times 10^{-7} Ms^{-1}$
  4. $3 \times 10^{-9} Ms^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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

What is the unit for the rate constant of a second order 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. $\displaystyle { mol }^{ 2 }{ L }^{ -2 }{ s }^{ -2 }$
Reveal answer Fill a bubble to check yourself
D Correct answer
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 }  $

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

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

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
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.