Chemical Kinetics Test

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Chemical Kinetics Test - 68

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Weekly Quiz Competition

Question 1
1 / -0

For a chemical reaction to occur, all of the following must happen except:

A
A large enough number of collisions must occur

B
Chemical bonds in the reactants must break

C
Reactant particles must collide which enough energy for change to occur

D
Reactant particles must collide with correct orientation

Solution

For a chemical reaction to occur, bonds must break in reactant so that new bonds are formed. Moreover, reactants must collide with energy greater than activation energy for change to occur. Also, reactant must have proper orientation for reaction.

However, it is not necessary that enough number of collisions must occur.
Question 2
1 / -0

Consider figure and mark the correct option.

A
Activation energy of forward reaction is $$E_{1} + E_{2}$$ and product is less stable than reactant

B
Activation energy of forward reaction is $$E_{1} + E_{2}$$ and product is more stable than reactant

C
Activation energy of forward and backward reaction is $$E_{1} + E_{2}$$ and product is more stable than reactant

D
Activation energy of backward reaction is $$E_{1}$$ and product is more stable than reactant

Solution

The product is less stable since the forward reaction is not favorable. The reaction is endothermic ($$\Delta H>0$$).

Option A is correct.
Question 3
1 / -0

For reaction $$A \rightarrow B$$, the rate law expression is $$-\dfrac{d[A]}{dT}=k[A]^{1/2}$$. If initial concentration of $$[A]$$ is $$[A]_0$$ then, which of the following statement is incorrect?

A
The integrated rate expression is $$k=2/t(A^{1/2}_0-A^{1/2})$$

B
The graph of $$\sqrt{A}$$ vs $$t$$ will be

C
The half life period $$t_{1/2}=\dfrac{k}{2[A]_o^{1/2}}$$

D
The time taken for $$75\%$$ completion of reaction $$t_{3/4}=\dfrac{\sqrt{A_o}}{K}$$

Solution

From the rate law,

$$R=K[A]^{1/2}$$

Thus order of Reaction is, $$n=1/2$$

General formula for $$t_{1/2}$$

$$t_{1/2}=\cfrac {2^{n-1}-1}{K[A_o]^{n-1}}$$ or $$t_{1/2} \propto \cfrac {1}{[A]^{n-1}}$$

For, $$n= 1/2$$

$$t_{1/2} \propto \cfrac {1}{[A_o]^{1/2-1}} \Rightarrow t_{1/2} \propto \cfrac {1}{[A_o]^{-1/2}}$$

or, $$t_{1/2} \propto [A_o]^{1/2}$$

Thus, statement C is incorrect.
Question 4
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Rate of formation of $${ SO }_{ 3 }$$ according to the reaction $$2{ SO }_{ 2 }+O_{ 2 }\rightarrow 2{ SO }_{ 3 }\quad is\quad 1.6\times { 10 }^{ -3 }kg\quad min^{ -1 }$$. Hence rate at which $$SO_{ 2 }$$ reacts is:

A
$$1.6\times { 10 }^{ -3 }kg\quad { min }^{ -1 }$$

B
$$8.0\times { 10 }^{ -4 }kg\quad { min }^{ -1 }$$

C
$$3.2\times { 10 }^{ -3 }kg\quad { min }^{ -1 }$$

D
$$1.28\times { 10 }^{ -3 }kg\quad { min }^{ -1 }$$

Solution

$$2 SO_2 + O_2 \rightleftharpoons 2 SO_3$$

$$\dfrac{1}{2}\dfrac{d[SO_3]}{dt} = 1.6 \times 10^{-3} kg/min = \dfrac{1.6 \times 10^{-3}}{80} mol/min$$ $$[\because M_{SO_3}= 80 \times 10^{-3} Kg/mol]$$

$$\dfrac{-1}{2}\dfrac{d[SO_2]}{dt} = \dfrac{+1}{2}\dfrac{d[SO_3]}{dt}$$

$$= -\dfrac{1.6 \times 10^{-3}}{80 \times 10} $$ mol/min

$$= -\dfrac{1}{50} \times 64 \times 10^{-3} = -1.28 \times 10^{-3} $$ kg/min
Question 5
1 / -0

Directions For Questions

A group of mountain climbers set up a camp at 3 km altitude and experience a barometric pressure of $$0.69atm$$. They discover that pure water boils at $$90^oC$$ and it takes $$300min$$ of cooking to make a "three-minute" egg.

...view full instructions

What is the activation energy for this change?

A
$$62.4\ kcal$$

B
$$2.60\ kcal$$

C
$$25.9\ kcal$$

D
None of these

Solution
Question 6
1 / -0

Which of the following reaction has zero activation energy?

A
$${ CH }_{ 4 }+\overset { \bullet }{ C } l\rightarrow \overset { \bullet }{ C } { H }_{ 3 }HCl$$

B
$${ Cl }_{ 2 }\rightarrow 2Cl$$

C
$$\overset { \bullet }{ C } { H }_{ 3 }+\overset { \bullet }{ C } { H }_{ 3 }+{ CH }_{ 3 }+{ CH }_{ 3 }$$

D
$$\overset { \bullet }{ C } { H }_{ 3 }+Cl-Cl\rightarrow { CH }_{ 3 }+Cl+\overset { \bullet }{ C } l$$

Solution

Among the given reactions
$${ \dot { CH } }_{ 3 }+{ \dot { CH } }_{ 3 }\rightarrow { CH }_{ 3 }-{ CH }_{ 3 }$$ has zero activation energy.
All the other reactions are following a free radial which needs energy in the form $$U.V$$ light which is high activation energy.
Where as in the above reaction the free radicals are bonded together by lowering their energy thus by increasing the stability.
So, the reaction
$${ \dot { CH } }_{ 3 }+{ \dot { CH } }_{ 3 }\rightarrow { CH }_{ 3 }-{ CH }_{ 3 }$$ has zero activation energy.
Question 7
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The activation energy of a reaction is $$58.3\ kJ/mole$$. The ratio of the rate constants at $$305K$$ and $$300K$$ is about:
[$$R=8.3\ J{k}^{-1}{mol}^{-1}$$ and Antilog $$0.1667=1.468$$]

A
$$1.25$$

B
$$1.75$$

C
$$1.5$$

D
$$2.0$$

Solution

$$log\quad \frac { { K }_{ 2 } }{ { K }_{ 1 } } =\frac { { E }_{ o } }{ 2.303\quad X\quad R } \quad \left[ \frac { { T }_{ 2 }-{ T }_{ 1 } }{ { T }_{ 1 }{ T }_{ 2 } } \right] $$

$$=\quad \frac { 58.3 }{ 2.303\quad X\quad 8.3 } \left[ \frac { 305-300 }{ 305\quad X\quad 300 } \right] $$

$$=\quad 3.0499\quad X\quad 5.4644\quad X\quad 1{ 0 }^{ -5 }$$

$$=1.666\quad X\quad 1{ 0 }^{ -4 }$$

=$$log\quad \frac { { K }_{ 2 } }{ { K }_{ 1 } } =0.1666\quad X\quad 1{ 0 }^{ -3 }$$

=$$\frac { { K }_{ 2 } }{ { K }_{ 1 } } =antilog(0.1666)$$

$$=1.468\approx 1.5$$

Hence, 1.5 is the answer.
Question 8
1 / -0

A reaction takes place in three steps with the rate constant $$k_1, k_2$$ and $$k_3$$. The overall rate constant $$k=\dfrac{k_1(k_2)^{1/2}}{k_3}$$. If activation energies are $$40, 30$$ and $$20\ kJ$$ for step $$I, II$$ and $$III$$ respectively, the overall activation energy of reaction will be:

A
10

B
15

C
30

D
35

Solution

Over all activation energy

$$=E_{1}+\dfrac{E_{2}}{2}-E_{3}$$

$$=40+\dfrac{30}{2}-20$$

$$=35 KJ$$
Question 9
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Which of the following reactants can be used to distinguish between benzaldehyde and Benzyl alcohol?

A
$${KMnO}4$$

B
$${Cr}_2{O}_4$$

C
Sodium metal

D
All

Solution
Question 10
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It is often stated that, near room temperature, a reaction rate doubles if the temperature increases by $${ 10 }^{ \circ }C$$ Calculate the activation energy of a reaction that obeys this rule exactly.

A
$$12.4 kcal$$

B
$$24.8 kcal$$

C
$$6.7 kcal$$

D
$$49.6 kcal$$