Tag: enzymes and catalysts

Questions Related to enzymes and catalysts

The substance which decreases the rate of a chemical reaction is called: 

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

  1. inhibitor

  2. poison

  3. moderator

  4. promoter

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Correct Option: A
Explanation:

The substance which decreases the rate of a chemical reaction is called inhibitor e.g. anti-oxidants are added as inhibitors to food substances to stop its spoilage from exposure oxygen. Similarly, protective coatings on metal surfaces inhibit the corrosion of metals by preventing their interaction with the air and water. An inhibitor is an opposite of a catalyst.

In the reaction, $KMnO _4 + H _2SO _4 + H _2C _2O _4\xrightarrow{Mn^{2+}}$ Products, $Mn^{2+}$ ions act as:

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

  1. positive catalyst

  2. negative catalyst

  3. autocatalyst

  4. enzyme catalyst

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Correct Option: C
Explanation:

Purple permanganate ions are reduced in acidic solution by oxalate ions to the nearly colorless manganese(II) ions, whereas the oxalate ions are oxidized to gaseous carbon dioxide: Obviously, the $Mn^{2+}$  ions act as catalyst. The reaction rate increases gradually even when no $Mn^{2+}$ ions are added because they are formed during the reaction meaning this product autocalyzes its own formation. 

Efficiency of the catalyst depends on its: 

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

  1. molecular weight

  2. number of free valencies

  3. physical state

  4. amount used

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Correct Option: B
Explanation:

The distribution of free bonds on the catalyst surface is not uniform. These are crowded at the 'peaks', cracks' and corners of the catalyst. The catalytic activity due to adsorption of reacting molecules is maximum at these spots. These are, therefore, referred to as the active centers. The active centers i.e free valencies increase the rate of reaction not only by increasing the concentration of the reactants, but they also activate the molecule adsorbed at two such centers by stretching it.

The decomposition of hydrogen peroxide can be slowed down by the addition of a small amount of acetamide. The added acetamide acts as:

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

  1. inhibitor

  2. promoter

  3. moderator

  4. poison

Show answer
Correct Option: A
Explanation:

The chemical substance added to another substance, to slow down a reaction or to prevent an unwanted chemical change is called inhibitor. The decomposition of hydrogen peroxide. Unwanted chemical change can be slowed down by the addition of a small amount of acetamide. The latter acts as an inhibitor.

In chemical reaction, the catalyst: 

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

  1. alters the amount of product

  2. lowers the activation energy

  3. decreases $A$ of forward reaction

  4. increases $A$ of forward reaction

Show answer
Correct Option: B
Explanation:

A catalyst is the substance which speed up the chemical reaction by lowering the activation energy of reaction but it do not effects the amount of forward and backward reaction.
Hence option B is correct.

An example of an autocatalytic reaction is: 

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

  1. hydrogenation of oils

  2. decomposition of nitroglycerine

  3. oxidation of $Na _3AsO _3$ in presence of $Na _2SO _3$

  4. thermal decomposition of $KClO _3$ in presence of $MnO _2$

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Correct Option: B
Explanation:

Reaction mechanism for the decomposition of nitroglycerine $4C _3H _5N _3O _9 \rightarrow 6N _2 + 12CO _2 + 10H _20 + O _2$.
This reaction is auto catalytic which is based upon internal redox chemistry.

Which acts as poison for Pd-charcoal in Lindlar's catalyst?

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

  1. $BaSO _4$

  2. Quinoline

  3. Both $A$ and $B$

  4. None of the above

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Correct Option: D
Explanation:

A Lindlar catalyst is a heterogeneous catalyst which  consists of palladium deposited on calcium carbonate which is then poisoned with various forms of lead or sulphur not with $BaSO _4$ and quiniline. It is used for the hydrogenation of alkynes to alkenes.

The efficiency of an enzyme in catalysing a reaction is due to its capacity: 

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

  1. to form a strong enzyme substrate complex

  2. to decrease the bond energies in the substrate molecule

  3. to change the shape of the substrate molecule

  4. to lower the activation energy of the reaction

Show answer
Correct Option: D
Explanation:

Enzymes are biological molecules (typically proteins) that significantly speed up the rate of virtually all of the chemical reactions that take place within cells by lowering the activation energy required for the reaction. It alters the pathway but doesn't take part in the reaction.

Which is not the characteristic of a catalyst?

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

  1. It changes the equilibrium point.

  2. It initiates the reaction.

  3. It alters the rate of reaction.

  4. It increases the average K.E. of molecules.

Show answer
Correct Option: A
Explanation:

A catalyst is a substance which speed up the chemical reaction by lowering the activation energy of reaction but it does not change the equilibrium point.

Hence, the correct option is $\text{A}$

Regarding criteria of catalysis which one of the following statements is not true?

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

  1. The catalyst is changed chemically during the reaction.

  2. A small quantity of catalyst is often sufficient to bring about a considerable amount of the reaction.

  3. In reversible reaction, the catalyst alters the equilibrium position.

  4. The catalyst accelerates the rate of reaction.

Show answer
Correct Option: C
Explanation:

The effect of catalyst is to increase speed of reaction by lowering the activation energy
As it affect forward and backward reaction equally hence it don't change any thermodynamical aspects of reaction.
Further catalyst don't take part in reaction so it don't change the final products.