Tag: dependence of reaction rate on concentration of reactants

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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 the reaction, $C{ Cl } _{ 3 }CHO+NO\longrightarrow CH{ Cl } _{ 3 }+NO+CO$, is given by the equation, rate $=k\left[ C{ Cl } _{ 3 }CHO \right] \left[ NO \right] $. If concentration is expressed in ${mol}/{litre}$, the unit of $k$ is:

  1. ${ mol }^{ -2 }{ L }^{ 2 }{ s }^{ -1 }$
  2. $mol$ ${ L }^{ -1 }{ s }^{ -1 }$
  3. $L$ ${ mol }^{ -1 }{ s }^{ -1 }$
  4. ${ s }^{ -1 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since it is second order reaction as clear by rate equation so unit of $k$ is given by $M^{-1} s^{-1}$ or $L\space mol^{−1}s^{−1}$

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

Units of rate constants for first and zero order reactions in terms of molarity $M$ unit are respectively:

  1. ${ sec }^{ -1 },M\ { sec }^{ -1 }$
  2. ${ sec }^{ -1 },M$
  3. $M\ { sec }^{ -1 },{ sec }^{ -1 }$
  4. $M,{ sec }^{ -1 }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$K=\frac{dx}{dt[A]} $ for Ist order = $sec^{−1}$
$ K = \frac{dx}{dt}$ for zero order = $mol \space litre^{−1}sec^{−1}$

Hence A is the correct answer.

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

Consider the reaction, $2A+B\longrightarrow $ Products. When the concentration of $B$ alone was doubled, the half-life did not change. When the concentration of $A$ alone was doubled, the rate increased by two times. The unit of the rate constant for this reaction is:

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

  3. Unitless
  4. $mol$ ${ L }^{ -1 }{ s }^{ -1 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Concentration change in '$B$' does not change half life, it means the reaction is first order with respect to $B$. When concentration of only '$A$' is doubled, the rate of reaction becomes double, thus order with respect to $A$ will also be one.
Overall order of reaction $=2$
Unit of rate constant $=L$ ${ mol }^{ -1 }{ s }^{ -1 }$

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

Consider following two reactions:
$A\longrightarrow $ Product,         $-\dfrac { d\left[ A \right]  }{ dt } ={ k } _{ 1 }{ \left[ A \right]  }^{ 0 }$
$B\longrightarrow $ Product,         $-\dfrac { d\left[ B \right]  }{ dt } ={ k } _{ 2 }{ \left[ B \right]  }^{ 1 }$
${ k } _{ 1 }$ and ${ k } _{ 2 }$ are expressed in terms of molarity $\left( mol\ { L }^{ -1 } \right) $ and time $\left( { s }\right) $ as:

  1. ${ s }^{ -1 },M{ s }^{ -1 }{ L }^{ -1 }$
  2. $M{ s }^{ -1 },M{ s }^{ -1 }$
  3. ${ s }^{ -1 },{ M }^{ -1 }{ s }^{ -1 }$
  4. $M{ s }^{ -1 },{ s }^{ -1 }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The units of rate of reaction is $Ms^{-1}$.

For zero order reaction, unit of K, will be $Ms^{-1}$
For 1st order reaction, unit of $K _2$ will be $s^{-1}$

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

Rate law expression of a reaction is:
            Rate $=k{ \left[ A \right]  }^{ { 2 }/{ 3 } }\left[ B \right] $
Which of the following are correct about the corresponding reaction?

  1. Order of reaction $=\dfrac { 2 }{ 3 } +1=\dfrac { 5 }{ 3 } $
  2. Unit of rate constant $={ L }^{ { 2 }/{ 3 } }{ mol }^{ { -2 }/{ 3 } }{ sec }^{ -1 }$
  3. Unit of rate constant $={ atm }^{ { -2 }/{ 3 } }{ sec }^{ -1 }$
  4. Unit of rate constant $=mol$ ${ L }^{ -1 }{ sec }^{ -1 }$
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Overall order=$\frac{2}{3}+1=\frac{5}{3}$

Unit of rate constant=$mol^{1-n}L^{n-1}sec^{-1}$
where n=order of reaction
For given reaction, unit of rate constant=$mol^{1-5/3}L^{5/3-1}sec^{-1}$
=$L^{2/3}mol^{-2/3}sec^{-1}$
For gaseous reaction, concentration term= pressure in atm
unit of rate constant=$atm^{-2/3}sec^{-1}$

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

Mechanism of a hypothetical reaction $X _2+Y _2\rightarrow 2XY$ is given below;
(i) $ X _2\rightarrow X+X$ (fast)
(ii) $X+Y _2\rightleftharpoons XY+Y$ (slow)
(iii) $ X+Y \rightarrow XY$ (fast)
The overall order of the reaction will be: 

  1. $2$
  2. $0$
  3. $3$
  4. $1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Order of Reaction is given by the slowest step of Reaction. In slowest step we 

have 2 reactants so, $2^{nd}$ order reaction. 

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

A reaction, which is second-order, has a rate constant of $0.002  L\, mol^{-1}\, s^{-1}$. If the initial conc. of the reactant is 0.2 M, how long will it take for the concentration to become 0.0400 M?

  1. 1000 sec

  2. 400 sec

  3. 200 sec

  4. 10,000 sec
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
$\dfrac{1}{a}=\dfrac{1}{a _{0}}+kt$
$\dfrac{1}{0.04}=\dfrac{1}{0.2}+0.002t$
$t=10000sec$
Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

For the reaction $CO(g)+2{ H } { 2 }(g)\rightleftharpoons { CH } _{ 3 }OH(g)$. If active mass of $CO$ is kept constant and active mass of ${H} _{2}$ is tripled, the rate of forward reaction will become _____ of its initial value.

  1. three times

  2. six times

  3. eight times

  4. nine times
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For the following reaction, Rate is defined as


$rate = k[CO][{{H} {2}}]^{2}$
Now, the active mass of CO is kept constant and active mass of {H}{2} is tripled. Now the rate is,

${rate}^{'} =k[CO][{3 \times {H} _{2}}]^{2}$
${rate}^{'} = 9 \times rate$
 
So, the rate of forward reaction will become nine times of its initial value.

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

The reaction $2{NO} _{(g)}+{H} _{2(g)}\longrightarrow {N} _{2}{O} _{(g)}+{H} _{2}{O} _{(g)}$ follows the rate law $\cfrac { d{ P } _{ \left( { N } _{ 2 }O \right)  } }{ dt } =k{ \left( { P } _{ NO } \right)  }^{ 2 }{ p } _{ { H } _{ 2 } }$. If the reaction is initiated with ${P} _{NO}=1000mm$ $Hg$ and ${ p } _{ { H } _{ 2 } }=10mm$ $Hg$, then the reaction will follow:

  1. third order kinetics

  2. second order kinetics

  3. first order kinetics

  4. zero order kinetics
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The rate law is given as Rate = k[P_NO]^2 [P_H2]. Since the initial concentration of NO (1000 mm Hg) is much larger than the concentration of H2 (10 mm Hg), the concentration of NO remains effectively constant throughout the reaction. Thus, the reaction behaves as pseudo-first order with respect to H2.

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

The following data were obtained for the saponification of ethyl acetate using equal concentrations of ester and alkali. The reaction order is:

Time(min) 0 4 10 20
Vol. of acid(mL)  8.04 5.30 3.50 2.22

  1. 0

  2. 1

  3. 2

  4. 3
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Saponification of ethyl acetate with equal concentrations of ester and alkali is a classic second-order reaction. The data provided would show a linear relationship for 1/[concentration] vs time, confirming second-order kinetics.