Tag: surface chemistry

Questions Related to surface chemistry

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.

The catalyst is a substance which:

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

  1. increases the yield of the reaction

  2. increases the speed of the reaction

  3. decreases the speed of the reaction

  4. increases the speed of the reaction and remains unchanged.

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Correct Option: D
Explanation:

Catalyst is a substance that changes (usually increases) the rate of a reaction, without being involved in the reaction. A catalyst provides large surface area to one of the reactants, providing it an exposure to be reacted upon by the other reactant.

During hydrogenation reaction, H-H bond splits and hydrogen atoms are attached to Ni catalyst through through strong chemical forces.

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:

In hydrogenation reaction, the H-H bond splits and the hydrogen atom is chemically bonded to the Ni catalyst.

Here the Ni catalyst provides the surface on which reaction takes place.

During hydrogenation reaction, H-H bond splits and hydrogen atoms are attached to Ni catalyst through weak van der Waal forces.

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: B
Explanation:
During the hydrogenation, the H-H bond split and the hydrogen atoms get attached to the Ni catalyst through chemical bonding.
Thus the given statement is false.

Which of the following statements about catalysts is true?

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

  1. They increase the value of the equilibrium constant.

  2. They increase the amount of product present at equilibrium.

  3. They increase the concentration of the reactants.

  4. They are permanently altered as the reaction proceeds.

  5. They reduce the activation energy of the reaction.

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Correct Option: E
Explanation:

Catalysts reduce the activation energy of the reaction by providing an alternate pathway having lower activation energy.
Thus, catalysts alter the mechanism of the reaction.