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

A 22.4 litre flask contains 0.76 mm of ozone at $25^oC$. Calculate:
(i) the concentration of oxygen atom needed so that the reaction, $O+O _3\rightarrow 2O _2$ having rate constant equal to $1.5\times 10^7$ litre $mol^{-1} sec^{-1}$ can proceed with a rate of 0.15 mol $litre^{-1} sec^{-1}$
(ii) the rate of formation of oxygen under this condition.

  1. (i) $2.45\times 10^{-4}$, (ii) $0.30 mol L^{-1} t^{-1}$
  2. (i) $4.9\times 10^{-4}$, (ii) $0.60 mol L^{-1} t^{-1}$
  3. (i) $2.45\times 10^{-5}$, (ii) $0.30 mol L^{-1} t^{-1}$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\displaystyle [O _3] = \frac {P}{RT} = \frac {0.76}{760 \times 0.0821 \times 298} = 4.08 \times 10^{-5} $
$\displaystyle [O] = \frac {rate}{k \times [O _3]} = \frac {0.15}{1.5 \times 10^{7} \times 4.08 \times 10^{-5} = 2.45 \times 10^{-4}  }$
The rate of formation of oxygen under this condition is equal to twice the rate of the reaction.
It is equal to $\displaystyle 2 \times 0.15 : mol litre^{-1} sec^{-1} = 0.30 : mol litre^{-1} sec^{-1} $

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

The unit and value of rate constant and that of rate of reaction are same for:

  1. first order

  2. zero order

  3. second order

  4. all are wrong
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As we know,
For zero order reaction, $\frac {dx}{dt}=K$.
so, unit and value of rate constant and that of rate of reaction are same for zero order.

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 $n^{th}$ order has units:

  1. $Litre^{-1} mol^{1-n} sec^{-1}$
  2. $Mol^{1-n} litre^{1-n} sec^{-1}$
  3. $Mol^{1-n} litre^{n-1} sec^{-1}$
  4. $Mol^{1-n^{2}} litre^{n^{2}} sec^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As we know,
For nth order; unit of rate constant may be derived by
$K=\frac {rate}{[reactant]^n}$
$=Mol^{1-n} litre^{n-1} sec^{-1}$

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

A reaction proceeds in three stages. The first stage is slow and involves two molecules of reactants. The second and third stage are fast. The overall order of the reaction is:

  1. first order

  2. second order

  3. third order

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

The overall order of the reaction is second order.
Reactions are proceeded in many steps, it does not means that no. of step will be equal to order of reaction. But rate is determined only by slow step of mechanism.

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, $A+B+C\rightarrow P$; is given by; $r=-\frac {d[A]}{dt}=K[A]^{1/2}[B]^{1/2}[C]^{1/4}$. The order of the reaction is:

  1. 1

  2. 2

  3. 1/2

  4. 5/4
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As we know,

For a reaction, $A+B\rightarrow Product$, if rate $=K[A]^m[B]^n$, the order of reaction $=m+n$.

So here for the given reaction, order of reaction $= 1/2+1/2+1/4 = 5/4$

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

If the concentration is measured in mol $L^{-1}$ and time in minutes, the unit for the rate constant of a third order reaction is:

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

As we know,
$k\, =\, [conc]^{1-n}\, min^{-1}$
For third order reaction = $[mol\, L^{-1}]^{1-3}\, min^{-1}$
$L^2\, mol^{-2}\, min^{-2}$

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

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

  1. First order reaction

  2. Second order reaction

  3. Third order reaction

  4. Zero order reaction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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

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