Surface Chemistry Test

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Surface Chemistry Test - 20

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Weekly Quiz Competition

Question 1
1 / -0

True statement is:

A
Positive catalyst increases the rate of reaction

B
During the course of the reaction, specific reaction rate remains constant.

C
Rate constant always increases with rise in temperature whether the reaction is endothermic or exothermic.

D
All are correct.

Solution

(A) Positive catalyst increases the rate of reaction. It increases the rate of forward as well as reverse reaction. Hence, equilibrium is quickly attained.
(B) During the course of the reaction, specific reaction rate remains constant. It is independent of the reactant concentration and varies only with temperature.
(C) Rate constant always increases with rise in temperature whether the reaction is endothermic or exothermic. This is in accordance with Arrhenius equation which gives the temperature dependence of reaction rates.
Hence, all the statements are correct.
Question 2
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The efficiency of an enzyme in catalyzing a reaction is due to its capacity_____________.

A
To form a strong enzyme-substrate complex

B
To decrease the bond energy of all substrate molecules

C
To change the shape of the substrate molecule

D
To lower the activation energy of the reaction

Solution

A catalyst is a substance, which increases the rate of reaction without itself being consumed at the end of the reaction, and the phenomenon is called catalysis. There are some catalysts which decrease the rate of reaction and such catalysts are called negative catalyst. Obviously, the catalyst accelerating the rate will be positive catalyst. However, the term positive is seldom used and catalyst itself implies positive catalyst.
Enzymes acts as catalyst for biological process and lower activation energy and it increases efficiency.
Question 3
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Burning of coal is represented as $$C(s)\, +\, O_2(g)\, \rightarrow\, CO_2(g).$$ The rate of this reaction is increased by:

A
Decreasing in the concentration of oxygen

B
Powdering the lumps of coal

C
Decreasing the temperature of coal

D
Providing inert atmosphere

Solution

FACTORS AFFECTING THE RATE OF REACTION:
(i) Concentration : Law of mass action enunciates that greater is the conc. of the reactants, the more rapidly the reaction proceeds.

(ii) Pressure (Gaseous reaction) : On increasing the pressure, volume decreases and conc. increases and hence the rate increases.

(iii) Temperature : It is generally observed that rise in temperature increases the reaction rate.

(iv) Nature of the reactants : The rate depends upon specific bonds involved and hence on the nature of reactants.

(v) Surface area of the reactants : In heterogeneous reactions, more powdered is the form of reactants, more is the velocity. [as more active centres are provided]

So, the rate of reaction will increase by powdering the lumps of coal as surface area increases in that case.
Question 4
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When $$KClO_3$$ is heated, it decomposes into $$KCl$$ and $$O_2$$. If some $$MnO_2$$ is added, the reaction goes much faster because:

A
$$MnO_2$$ decomposes to give $$O_2$$

B
$$MnO_2$$ provides heat by reacting

C
better contact is provided by $$MnO_2$$

D
$$MnO_2$$ acts as a catalyst

Solution

The decomposition of $$KClO_3$$ in presence of $$MnO_2$$ can be given as follow:

$$2KClO_3 \xrightarrow{MnO_2} 2KCl + 3O_2$$

In this reaction, the $$MnO_2$$ acts as a catalyst. Thus, it increases the rate of the reaction.

Hence, option D is correct.
Question 5
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Which of the following explains the increase of the reaction rate by catalyst ?

A
Catalyst decreases the rate of backward reaction so that the rate of forward reaction increases.

B
Catalyst provides extra energy to reacting molecules so that they may produce effective collisions.

C
Catalyst provides an alternative path o lower activation energy to the reactants.

D
Catalyst increases the number of collisions between the reacting molecules.

Solution

A catalyst is a substance, which increases the rate of reaction without itself being consumed at the end of the reaction, and the phenomenon is called catalysis. There are some catalysts which decrease the rate of reaction and such catalysts are called negative catalyst. Obviously, the catalyst accelerating the rate will be positive catalyst. However, the term positive is seldom used and catalyst itself implies positive catalyst.
Characteristics of catalyst are as follows:
i) A catalyst remains unchanged chemically at the end of reaction, however its physical state may change.
ii) A catalyst never initiate a chemical reaction. It simply influences the rate of reaction.
iii) A small quantity of catalyst is sufficient to influence the rate of reaction
iv) A catalyst does not influence the equilibrium constant of reaction. It simply helps in attaining equilibrium earlier. It alters the rate of forward & backward reactions equally.
v) Catalyst’s activity is more or less specific.
A catalyst for one reaction is not necessary to catalyse the another reaction.
Question 6
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Mark the correct statement in a reversible reaction:

A
A catalyst catalyzes the forward reaction.

B
A catalyst catalyzes the backward reaction.

C
A catalyst influences a direct and reverse reaction to the same extent.

D
A catalyst increases the rate of forward reaction and decreases the rate of backward reaction.

Solution

A catalyst is a substance, which increases the rate of reaction without itself being consumed at the end of the reaction, and the phenomenon is called catalysis. There are some catalysts which decrease the rate of reaction and such catalysts are called negative catalyst. Obviously, the catalyst accelerating the rate will be positive catalyst. However, the term positive is seldom used and catalyst itself implies positive catalyst. Catalysts are generally foreign substances but sometimes one of the product formed may act as a catalyst and such a catalyst is called "auto catalyst" and the phenomenon is called auto catalysis.
Question 7
1 / -0

A catalyst is used:

A
Only for increasing the velocity of a reaction

B
For altering the velocity of a reaction

C
Only for decreasing the velocity of a reaction

D
All (a), (b), and (c) are correct

Solution

A catalyst is a substance, which increases the rate of reaction without itself being consumed at the end of the reaction, and the phenomenon is called catalysis. There are some catalysts which decrease the rate of reaction and such catalysts are called negative catalyst. Obviously, the catalyst accelerating the rate will be positive catalyst. However, the term positive is seldom used and catalyst itself implies positive catalyst. Catalysts are generally foreign substances but sometimes one of the product formed may act as a catalyst and such a catalyst is called "auto catalyst" and the phenomenon is called auto catalysis.
Question 8
1 / -0

A catalyst is a substance which:

A
Increases the equilibrium concentration of the product

B
Changes the equilibrium constant of the reaction

C
Shortens the time to reach equilibrium

D
Supplies energy to the reaction

Solution

A catalyst is a substance, which increases the rate of reaction without itself being consumed at the end of the reaction, and the phenomenon is called catalysis. There are some catalysts which decrease the rate of reaction and such catalysts are called negative catalyst. Obviously, the catalyst accelerating the rate will be positive catalyst. However, the term positive is seldom used and catalyst itself implies positive catalyst. Catalysts are generally foreign substances but sometimes one of the product formed may act as a catalyst and such a catalyst is called "auto catalyst" and the phenomenon is called auto catalysis.
Question 9
1 / -0

An example of autocatalytic reaction is:

A
Decomposition of nitroglycerine

B
Thermal decomposition of $$KClO_3\, and\, MnO_2$$ mixture

C
Breakdown of $$^{14}C_6$$

D
Hydrogenation of vegetable oil using nickel catalysts

Solution

A chemical reaction is called autocatalytic if at least one of the reaction products acts as a catalyst in the same or in one of the coupled reactions.

$$N_2$$ is one of the products of decomposition of nitroglycerine plays the role of an autocatalyst.
Question 10
1 / -0

Which of the following statements regarding catalyst is not true?

A
A catalyst remains uncharged in composition and quantity at the end of the reaction.

B
A catalyst can initiate a reaction.

C
A catalyst does not alter the equilibrium in a reversible reaction.

D
Catalysts are sometimes very specific in respect of reaction.

Solution

A catalyst is a substance, which increases the rate of reaction without itself being consumed at the end of the reaction, and the phenomenon is called catalysis. There are some catalysts which decrease the rate of reaction and such catalysts are called negative catalyst. Obviously, the catalyst accelerating the rate will be positive catalyst. However, the term positive is seldom used and catalyst itself implies positive catalyst. Catalysts are generally foreign substances but sometimes one of the product formed may act as a catalyst and such a catalyst is called "auto catalyst" and the phenomenon is called auto catalysis.

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Surface Chemistry Test - 20

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Surface Chemistry Test - 20

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Question 1

Positive catalyst increases the rate of reaction

During the course of the reaction, specific reaction rate remains constant.

Rate constant always increases with rise in temperature whether the reaction is endothermic or exothermic.

All are correct.

Solution

Question 2

To form a strong enzyme-substrate complex

To decrease the bond energy of all substrate molecules

To change the shape of the substrate molecule

To lower the activation energy of the reaction

Solution

Question 3

Decreasing in the concentration of oxygen

Powdering the lumps of coal

Decreasing the temperature of coal

Providing inert atmosphere

Solution

Question 4

$$MnO_2$$ decomposes to give $$O_2$$

$$MnO_2$$ provides heat by reacting

better contact is provided by $$MnO_2$$

$$MnO_2$$ acts as a catalyst

Solution

Question 5

Catalyst decreases the rate of backward reaction so that the rate of forward reaction increases.

Catalyst provides extra energy to reacting molecules so that they may produce effective collisions.

Catalyst provides an alternative path o lower activation energy to the reactants.

Catalyst increases the number of collisions between the reacting molecules.

Solution

Question 6

A catalyst catalyzes the forward reaction.

A catalyst catalyzes the backward reaction.

A catalyst influences a direct and reverse reaction to the same extent.

A catalyst increases the rate of forward reaction and decreases the rate of backward reaction.

Solution

Question 7

Only for increasing the velocity of a reaction

For altering the velocity of a reaction

Only for decreasing the velocity of a reaction

All (a), (b), and (c) are correct

Solution

Question 8

Increases the equilibrium concentration of the product

Changes the equilibrium constant of the reaction

Shortens the time to reach equilibrium

Supplies energy to the reaction

Solution

Question 9

Decomposition of nitroglycerine

Thermal decomposition of $$KClO_3\, and\, MnO_2$$ mixture

Breakdown of $$^{14}C_6$$

Hydrogenation of vegetable oil using nickel catalysts

Solution

Question 10

A catalyst remains uncharged in composition and quantity at the end of the reaction.

A catalyst can initiate a reaction.

A catalyst does not alter the equilibrium in a reversible reaction.

Catalysts are sometimes very specific in respect of reaction.

Solution

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