Chemical Kinetics Test

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Chemical Kinetics Test - 82

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Weekly Quiz Competition

Question 1
1 / -0

If the order of the reaction $$x+y\xrightarrow[]{hv}xy$$ is zero, it means that the rate of ____

A
Reaction is independent of temperature

B
Formation of activated complex is zero

C
Reaction is independent of the concentration of reacting species

D
Decomposition of activated complex is zero

Solution

In photochemical reactions the rate of reaction is independent of the concentration of reacting species.
Question 2
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Which the following statements is true for a first order reaction?

A
The rate of reaction is directly proportional to the zero power of concentration of the reactants.

B
The unit of rate constant is $$mol\ L^{-1}s^{-1}$$.

C
The half life of a reaction does not depend on the initial concentration of reactants .

D
Cannot be said directly.

Solution
Question 3
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Fill in the blanks by choosing the correct option:

Order of the reaction is the $$ \underline {X} $$ of the powers to which concentration terms are raised in experimentally determined rate equation. The unit of first order rate constant is $$ \underline {Y} $$. The units of first order rate constant when concentration is measured in terms of pressure and time in minute is $$ \underline {Z} $$

A
$$ X \rightarrow product, Y \rightarrow mol L^{-1} time^{-1} , Z \rightarrow atm min^{-1} $$

B
$$ X \rightarrow sum, Y \rightarrow mol L^{-1} time^{-1} , Z \rightarrow atm min^{-1} $$

C
$$ X \rightarrow product, Y \rightarrow L mol^{-1} time^{-1} , Z \rightarrow atm min^{-1} $$

D
$$ X \rightarrow sum, Y \rightarrow time^{-1} , Z \rightarrow min^{-1} $$

Solution
Question 4
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Cyclopropane rearranges to form propene
$$ \Delta \rightarrow CH_3 -CH =CH_2 $$
this follows first order kinetics. the rate constant is $$ 2.714 \times 10^{-3} sec^{-1} $$the initial concentration of cyclopropane is $$ 0.29 M $$what will be concentration of cyclopropane after 100 sec ?

A
$$ 0.035 M $$

B
$$ 0.22 M $$

C
$$ 0.145 M $$

D
$$ 0.0018 M $$

Solution

$$ k = \dfrac { 2.303}{t} log \dfrac {a}{(a-x) } $$

$$ (a-x) $$ is the concentration left after $$ 100 sec $$

$$ 2.7 \times 10^{-3} = \dfrac { 2.303}{ 100} log \dfrac { 0.29}{ (a-x) } $$

$$ \Rightarrow \dfrac { 0.27}{ 2.303} = log \dfrac { 0.29}{ (a-x) } \Rightarrow 0.117 = log \dfrac { 0.29}{ (a-x) } $$

$$ \Rightarrow (a-x) = 0.22 M $$
Question 5
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the half - life of the reaction $$ X \rightarrow Y $$ following first order kinetics , when the initial concentration of X is $$ 0.01 mol L^{-1} $$ and initial rate is $$ 0.00352 mol L^{-1} min^{-1} $$ will be

A
$$ 19.69 min $$

B
$$ 1.969 min $$

C
$$ 7.75 min $$

D
$$ 77.5 min $$

Solution

$$ \dfrac {dx}{dt} = k[X] $$

$$ 0.00352 = k \times 0.01 \Rightarrow k = 0.352 $$

$$ t_{1/2} = \dfrac { 0.693}{k} = \frac { 0.693}{ 0.352} = 1.969 min $$

Option B is correct.
Question 6
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the rate constant for a first order reaction is $$ 2 \times 10^{-2} min^{-1} $$ the half -life period of reaction is

A
$$ 69.3 min $$

B
$$ 34.65 min $$

C
$$ 17.37 min $$

D
$$ 3.46 min $$

Solution

$$Given:k=2\times10^{-2}min^{-1}$$

$$ t_{1/2} = \dfrac { 0.693}{k} = \dfrac { 0.693}{ 2 \times 10^{-2} } = 34.64 min $$

Option B is correct.
Question 7
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Rate constant in case of first order reaction is

A
inversely proportional to the concentration units

B
independent of concentration units

C
directly proportional to concentration units

D
inversely proportional to the square of concentration units

Solution

Option B is correct.
Question 8
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Which of the following is incorrect statement ?

A
Stoichiometry of a reaction tells about the order of the elementary reactions

B
For a zero order reaction, rate and the rate constant are idneitcal.

C
A zero order reaction is controlled by factors other than concentration of reactants

D
A zero order reaction is an elementary reaction

Solution

Elementary reactions that occur are unimolecualar and biomolecular ones,
where unimolecular may include bond dissociation or cis - trans transetion Biomolecular reactions strictly involve two species In comparison, zero order
reactions are complex in nature. (e $$\mathrm{g}$$. involving an engyme in $$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$$
decomposition)
Thus option $$D$$ is incorrect statement.
Question 9
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The activation energy of the reaction, $$A + B \rightarrow C + D + 38kcal$$ is $$20$$ kcal, What would be the activation energy of the reaction,
$$C + D \rightarrow A + B$$

A
$$20\,kcal$$

B
$$-20 \,kcal$$

C
$$18\,kcal$$

D
$$58\,kcal$$
Question 10
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In a certain first-order reaction, $$B^{n+}$$ is getting converted to $$B^{(n+4)+}$$ in solution. The rate constant of this reaction is measured by titrating a volume of the solution with a reducing agent which reacts only with $$B^{n+}$$ and $$B^{(n+4)+}$$. In the process, it converts to $$B^{n+}$$ to $$B^{(n-2)+}$$ and $$B^{(n+4)+}$$ to $$B^{(n-1)+}$$,At $$t=0$$ the volume of reagent consumed is 55 ml and at $$t = 20$$ min, the volume used is 70.5 ml. The rate constant for the conversion of $$B^{n+}$$ of $$B^{(n+4)+}$$ (ln 2 = 0.7, ln 5 = 1.6)

A
$$0.2\,min^{-1}$$

B
$$0.8\,min^{-1}$$

C
$$0.01\,min^{-1}$$

D
$$0.08\,min^{-1}$$

Solution