Tag: chemistry

Questions Related to chemistry

For which of the following reactions, the units of rate constant and rate of reaction are same ?

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

  1. First order reaction

  2. Second order reaction

  3. Third order reaction

  4. Zero order reaction

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Correct Option: D
Explanation:

For zero order,
R = k[A]
Unit of rate = mol $L^{-1}\, t^{-1}$
Unit of zero order = mol $L^{-1}\, t^{-1}$

What is the order of reaction which has a rate expression as follows:
rate = k$[A]^{3/2}[B]^{-1}$

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

  1. $3/2$

  2. $1/2$

  3. Zero

  4. None of these

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Correct Option: B
Explanation:

rate = k$[A]^{3/2}[B]^{-1}$
OR = $\displaystyle \frac{3}{2}\, -\, 1\, =\, \frac{1}{2}$

If a reaction involves gaseous reactants and products, the units of its rate are:

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

  1. $atm$

  2. $atm$ $s$

  3. $atm$ $s^{-1}$

  4. $atm^2s^2$

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Correct Option: C
Explanation:

If a reaction involves gaseous reactants and products, the unit of its rate is $atm\ s^{-1}$. It represents the change in pressure (in atm units) in unit time ($1$ second).

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.