Tag: surface chemistry

Questions Related to surface chemistry

Statement $1$: A catalyst increases the equilibrium of a reaction.
Statement $2$: Catalysts only lower the activation energy of the forward reaction.

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

  1. Both Statement $1$ and Statement $2$ are correct and Statement 2 is the correct explanation of Statement $1$

  2. Both Statement $1$ and Statement $2$ are correct, but Statement $2$ is NOT the correct explanation of Statement $1$

  3. Statement $1$ is correct, but Statement $2$ is not correct

  4. Both the Statement $1$ and Statement $2$ are not correct

Show answer
Correct Option: D
Explanation:

Catalysts work by producing an alternative route for the reaction. This affects the forward and back reactions equally so there is not any change in equilibrium.

Further catalysts speed up both forward and reverse reactions otherwise its equilibrium constant get change which further change the equilibrium

Which of the following statement(s) is/are $NOT$ correct regarding chemical catalysts?

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

  1. They are not consumed during the chemical reaction.

  2. They cannot make non-spontaneous reactions occur.

  3. They do not have to be the same phase as the reactant molecules.

  4. They shift equilibrated reactions to the product's side.

Show answer
Correct Option: D
Explanation:

Catalyst only alters the pathway of reaction by lowering the activation energy. They don't use in any reaction and remain unconsumed after the reaction.

Since they are lowering the activation energy so reactants easily cross the barriers and make no-spontaneous reactions occur

It is not necessary that catalysts are in the same phase with reactants such catalysis called heterogeneous catalysis.
For eg. $2SO _2(g) \xrightarrow{Pt(s)} 2SO _3(g)$

The equilibrium constant does not change in reaction by the catalyst which means that equilibrium doesn't shift in any direction. Hence option D is not correct.

A catalyst:

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

  1. increases the free energy change in the reaction

  2. decreases the free energy change in the reaction

  3. does not increase or decrease the free energy change in the reaction

  4. can either decrease or increase the free energy change depending on what catalyst we use

Show answer
Correct Option: C
Explanation:

A catalyst is a substance which increases the free energy change(rate of reaction) in the reaction.But is not consumed by the reaction; hence a catalyst can be recovered chemically unchanged at the end of the reaction it has been used to speed up or catalyze.

Which of the following statements is more correct?

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

  1. A catalyst only accelerates the rate of a chemical reaction.

  2. A catalyst can retard the rate of a chemical reaction.

  3. A catalyst can control the speed of a reaction.

  4. A catalyst alters the speed of a reaction.

Show answer
Correct Option: D
Explanation:

A catalyst is a substance which increases (accelerate)  the rate of reaction.But is not consumed by the reaction; hence a catalyst can be recovered chemically unchanged at the end of the reaction it has been used to speed up, or catalyze. 

Which of the following statements is not true?

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

  1. The action of a catalyst is not specific.

  2. The catalyst does not alter the equilibrium.

  3. A small amount of catalyst is sufficient to catalyse large amounts of reactants.

  4. The catalyst initiates the reaction.

Show answer
Correct Option: A
Explanation:

All catalysts are specific for certain  reactants. A certain catalyst can react with a particular reactant only. All catalysts do not react with all reactants.
Hence option A is correct.

Edges and peaks are more effective in a catalyst because: 

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

  1. they have more free valencies

  2. they have limited number of atoms

  3. they have limited number of molecules

  4. none of the above

Show answer
Correct Option: A
Explanation:

Edges and peaks of catalyst are the interacting sites of catalysts with the reagents as they have free valencies.So edges and peaks are effective sites of catalysts.
Hence option A is correct

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

Show answer
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

Show answer
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

Show answer
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.