Tag: surface chemistry

Quizzes (6) Questions (144)

Questions Related to surface chemistry

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

The structural resemblence of substrate and inhibitor leads to______________ inhibition.

  1. non-competitive

  2. competitive
  3. both $A$ and $B$

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

Competitive Inhibitor - A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate.

Non-competitive Inhibitor - A non-competitive inhibitor is a substance that interacts with the enzyme, but usually not at the active site. The noncompetitive inhibitor reacts either remote from or very close to the active site.

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

The process which is catalysed by one of the product is called :

  1. acid - base catalysis

  2. autocatalysis

  3. negative catalysis

  4. homogeneous catalysis
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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.0
A chemical reaction is said to have undergone autocatalysis, if the reaction product itself is the catalyst for that reaction.

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

A catalyst increases the rate of a reaction by:

  1. increasing the activation energy of the reaction
  2. increasing the value of rate constants $(k _f$ and $k _b)$

  3. increasing the enthalpy change of the reaction

  4. decreasing the enthalpy change of the reaction
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A catalyst increases rate of reacting by decreasing activation energy. and increasing the enthalpy change of the reaction

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

Which of the following is used as autocatalyst

  1. $ KMnO _4 $
  2. $ AI _2O _3 $
  3. $ CaC _3 $

  4. All of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

KMnO4 is a classic example of an autocatalyst in the reaction between oxalic acid and acidified potassium permanganate, where Mn2+ ions produced during the reaction catalyze the process.

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

Which one of the following reactions is an example of auto-catalysis ?

  1. $2{ AsH } _{ 3 }(s)\rightarrow 2As(s)+3{ H } _{ 2 }(g)$
  2. ${ N } _{ 2 }(g)\rightarrow 3{ H } _{ 2 }(g)\overset { Fe(g) }{ \rightarrow } 2N{ H } _{ 3 }(g)$
  3. ${ 2SO } _{ 2 }(g)\rightarrow { O } _{ 2 }(g)\overset { NO(g) }{ \rightarrow } 2S{ O } _{ 3 }(g)$
  4. ${ C } _{ 12 }{ H } _{ 22 }{ O } _{ H }(l)+{ H } _{ 2 }O(l)\overset { { H }^{ - }(l) }{ \rightarrow } { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 }(l){ HC } _{ 6 }{ H } _{ 12 }{ O } _{ 6 }(l)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Auto-catalysis is defined as the reaction that is catalyzed by one of its product.  in auto-catalysis product of reaction acts as a catalyst for the reaction.  In auto-catalysis the initial rate of reaction rises as the catalytic product is formed instead of decreasing steadily.  

for example: the free arsenic produced by decomposition of arsine auto catalyses the reaction. The thermal decomposition of Arsine produces arsenic and hydrogen.  2AsH3 forms 2As + 3H2

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

In a reversible reaction, a catalyst:

  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.
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Catalyst alters the state of equilibrium.

  1. True

  2. False

  3. Ambiguous

  4. Data insufficient
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. internal energy

  2. threshold energy

  3. activation energy

  4. free energy
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. Reactant catalysis.

  2. Heat produced in the reaction catalysis.

  3. Product catalysis.

  4. Solvent catalysis.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
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.