Tag: chemical kinetics

Questions Related to chemical kinetics

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.

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

  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

Show answer
Correct Option: A
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} $

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

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

  1. first order

  2. zero order

  3. second order

  4. all are wrong

Show answer
Correct Option: B
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.

The rate constant of $n^{th}$ order has units:

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

  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. $Mol^{1-n^{2}} litre^{n^{2}} sec^{-1}$

Show answer
Correct Option: C
Explanation:

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

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:

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

  1. first order

  2. second order

  3. third order

  4. zero order

Show answer
Correct Option: B
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.

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:

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

  1. 1

  2. 2

  3. 1/2

  4. 5/4

Show answer
Correct Option: D
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 $= 1/2+1/2+1/4 = 5/4$

The rate constant of nth order has units:

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

  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. none of the above

Show answer
Correct Option: C
Explanation:

For nth order; unit of rate constant may be derived by
$rate  = k[a]^n$
$K=\frac {rate}{[reactant]^n}$.

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:

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

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

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

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

  4. $min^{-1}$

Show answer
Correct Option: B
Explanation:

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

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

Show answer
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

Show answer
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. $atm^2s^2$

Show answer
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).