Tag: enzymes and catalysts

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

In the titration between oxalic acid and acidified potassium permanganate, the manganous salt formed during the reaction and catalyses the reaction. The manganous salt acts as: 

  1. promoter

  2. positive catalyst

  3. autocatalyst

  4. none of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In the tit-ration between oxalic acid and acidified potassium permanganate, the manganous salt formed during the reaction and catalyses the reaction. The manganous salt acts as auto catalyst because the rate of reaction depends on the manganous ions formed,so manganous ions catlyze the reaction.
Hence option C is correct.

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

In case of autocatalysis: 

  1. reactant catalyses

  2. heat produced in the reaction catalyses

  3. product catalyses

  4. solvent catalyses
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Autocatalysis is the reaction where one of the products formed catalyzes the reaction. So in case of auto catalysis product catalyses the reaction. Hence catalysis of a reaction by one of its products is called autocatalysis.

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

Which of the following are correct about the catalyst?

  1. They participate in the reaction but recovered at last
  2. It does not affect $\Delta G $
  3. It increases $\Delta G $

  4. It alters the mechanism of reaction
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

The catalyst is the substance which increases the rate of reaction by lowering the activation energy which alters the mechanism of the reaction.

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

Which statement of the following is false for a catalyst?

  1. A catalyst can initiate a reaction.

  2. It does not alter the position of equilibrium in a reversible reaction.

  3. A catalyst remains unchanged in quality and composition at the end of the reaction.

  4. Catalysts are sometimes very specific in reaction.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst which is not consumed in the catalysed reaction and can continue to act repeatedly.It increase rate of forward as well as backward reaction.

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

In presence of a catalyst, the activation energy is lowered by 3 kcal at $27^o C$. Hence, the rate of reaction will increase by:

  1. 32 times

  2. 243 times

  3. 3 times

  4. 48 times
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$K={Ae}^{\dfrac{-Ea}{RT}}$ 

So Ratio, ${\dfrac{K _2}{K _1}}={e^\dfrac{(Ea _2-Ea _1)}{RT}}$
$\dfrac{K _2}{K _1}$=$e^{\dfrac{(3\times1000)}{(8.314\times300)}}$=$e^{{3000}/{2494}}$ = $e^{1.2}$ = $3.3$
Nearly 3 times.

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

Which of the following statements is correct about solid catalysts?

  1. Catalyst is required in equal amount as the reactants present in the reaction.

  2. Catalytic activity of a solid catalyst does not depend upon the extent of chemisorption.

  3. Desorption is not important for a solid to act as good catalyst.

  4. Same reactants may give different products by using different catalysts.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Substances, which accelerate the rate of a chemical reaction and themselves remain chemically and quantitatively unchanged after the reaction, are known as catalysts, and the phenomenon is known as catalysis.
  • For a given chemical reaction the amount of catalyst used is not necessarily to be equal to that of reactants.
  • Catalytic activity of a solid catalyst depends upon the extent of chemisorption because of the various bonds formed.
  • A catalyst is called a good catalyst if not only catalyses the reaction but also gives space for further reaction over its surface .i.e Desorption is a important characteristic.
  • It is not necessary that a reaction to give same products if we use different catalysts, for different cataysts the products may be different.
Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

An inhibitor is described as:

  1. a substance that slows down or stops a reaction

  2. a substance which inhibits the properties of a catalyst

  3. a substance formed during the reaction and does not participate in the reaction

  4. a substance which prevents formation of products in a reaction being most reactive
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A reaction inhibitor is a substance that decreases the rate of, or prevents, a chemical reaction. A catalyst, in contrast, is a substance that increases the rate of a chemical reaction.

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

Presence of traces of arsenious oxide ($As _{2}O _{3}$) in the reacting gases $SO _{2}$ and $O _{2}$ in presence of platinised asbestos in contact process acts as:

  1. catalytic promoter

  2. catalytic poison

  3. dehydrating agent

  4. drying agent.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  • Promoters are substances that enhance the activity of a catalyst while poisons decrease the activity of a catalyst.
  • In the manufacturing of sulfuric acid, a step involves the reaction of $SO _2$ and $O _2$ in presence of platinized asbestos to give $SO _3$
                    .i.e. $SO _2+O _2 \rightarrow SO _3$ 
In the above reaction if traces of arsenious oxide ($As _2O _3$)  is used then it acts as the catalytic poison by reducing the catalytic activity of Platinised asbestos.