Tag: adsorption theory of heterogeneous catalysis

Questions Related to adsorption theory of heterogeneous catalysis

In a reversible reaction, a catalyst:

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. increases the rate of the forward reaction only.

  2. increases the rate of the forward reaction to a greater extent than that of the backward reaction.

  3. increases the rate of the forward reaction and decreases that of the backward reaction to a different extent.

  4. increases the rate of the forward and backward reactions equally.

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Correct Option: D
Explanation:

In a reversible reaction, a catalyst increases the rate of the forward and backward reactions equally.
An increase in rate of reaction in forward direction by a catalyst for a reaction in equilibrium brings in an increase in concentration of products at faster rate and thus, rate of backward reaction also increases to same magnitude and the equilibrium position is not altered. In such reactions equilibrium constant does not alters.

Catalyst alters the state of equilibrium.

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. True

  2. False

  3. Ambiguous

  4. Data insufficient

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Correct Option: B
Explanation:

Option (B) is correct.
Catalyst does not alter the state of equilibrium. In the presence of a catalyst, both the forward and reverse reaction rates will speed up equally, thereby allowing the system to reach equilibrium faster. The addition of a catalyst has no effect on the final equilibrium position of the reaction.

The minimum energy level necessary to permit a reaction to occur is:

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. internal energy

  2. threshold energy

  3. activation energy

  4. free energy

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Correct Option: B
Explanation:

The minimum energy level necessary to permit a reaction to occur is called threshold energy.
Threshold energy is the energy level where some chemical/physical action happens. Threshold energy for production of a particle is the minimum kinetic energy a pair of traveling particles must have when they collide. The threshold energy is always greater than or equal to the rest energy of the desired particle.

Which of the following is/are not possible in case of auto-catalysis?

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. Reactant catalysis.

  2. Heat produced in the reaction catalysis.

  3. Product catalysis.

  4. Solvent catalysis.

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Correct Option: A,B,D
Explanation:
A Catalyst is a substance which acclerates the rate of a chemical reaction without undergoing any change in its chemical composition or massduring the reaction. A catalyst acclerates the rate of a reaction by lowering the activation energy.

Auto Catalysis : When one of the reaction product behave as catalyst for that reaction and increase the rate of reaction then the phenomenon is called autocatalysis.

Auto catalytic reactions are slow in the beginning but become increasingly rapid as the reaction proceeds.


A set of chemical reactions can be said to be collectively autocatalytic if a number of those reactions produce, as reaction products, catalysts for enough of the other reactions that the entire set of chemical reactions is self-sustaining given an input of energy and food molecules.

A single chemical reaction is said to have undergone autocatalysis or be autocatalytic, if the reaction product is itself the catalyst for that reaction. So, reactant catalysis and solvent catalysis is not possible. Only product catalysis is done.

Hence,option A,B nad D are correct.


Chemical equilibrium is ____ by a catalyst.

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. not affected

  2. affected

  3. some time affected

  4. none of the above

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Correct Option: A
Explanation:

Chemical equilibrium is not affected by a catalyst.
When a catalyst is used, the equilibrium is achieved faster but the value of the equilibrium constant remains unaffected.

In auto-catalysis, one of the ______ of the reaction acts as a catalyst.

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. intermediates

  2. products

  3. reactants

  4. none of the above

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Correct Option: B
Explanation:

 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 the auto catalysis.
In auto-catalysis, one of the products of the reaction acts as a catalyst.
For example, when oxalic acid is titrated with $\displaystyle KMnO _4 $ in presence of dil $\displaystyle H _2SO _4 $, the colour of $\displaystyle KMnO _4 $ first fades slowly and then faster due to the formation of $\displaystyle Mn^{2+} $ ions which act as auto catalyst.
$\displaystyle 2KMnO _4 + 3H _2SO _4 +5H _2C _2O _4 \rightarrow K _2O _4 +2MnSO _4 +8H _2O +10CO _2$

The activity of the enzyme is increased in the presence of certain substances known as co-enzymes or activators.
enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. True

  2. False

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Correct Option: A
Explanation:
Enzyme Catalysis:
The enzymes are also termed as biochemical catalysts and the phenomenon is known as biochemical catalysis. Enzymes are highly specific in nature.

Enzyme activators are molecules that bind to enzymes and increase their activity. They are the opposite of enzyme inhibitors. These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism.

Activation energy is always lowered by positive catalyst.
enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. True

  2. False

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Correct Option: A
Explanation:

The given statement is true.
Activation energy is always lowered by positive catalyst. This increases the rate of the reaction.

A catalyst remains unchanged chemically at the end of the reaction.
enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. True

  2. False

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Correct Option: A
Explanation:

The given statement is true.
A catalyst remains unchanged chemically at the end of the reaction. It may take part in the reaction mechanism. It may be consumed in the first step and regenerated in the second step.

For a catalyst which condition is not essential :

enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

  1. Variable valency

  2. High ionisation energy

  3. Empty orbitals

  4. Free valency on the surface

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Correct Option: B
Explanation:

For a catalyst, high ionization energy is not essential.
The essential conditions include variable valency, empty orbitals and free valency on the surface.