Tag: catalysis

Questions Related to catalysis

Which of the following statements about catalyst is incorrect?

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

  1. They have no effect on the value of the equilibrium constant

  2. They increase the amount of product present at equilibrium

  3. They provide an alternate pathway for effective collisions

  4. They lower the activation energy

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Correct Option: B

Which of the following statements does not accurately describe the action of a catalyst?

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

  1. A catalyst causes a reaction to proceed at a faster rate.

  2. A catalyst lowers the activation energy of a reaction.

  3. A catalyst affects the rate of both the forward and the reverse reaction.

  4. A catalyst increases the rate constant of a reaction.

  5. A catalyst increases the equilibrium constant of a reaction.

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Correct Option: E
Explanation:

Option E is the correct answer.

A catalyst does not really increase the equilibrium constant of a reaction. It just increases\decreases the rate of the reaction by lowering\raising its activation energy.

A catalyst:

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

  1. changes $\Delta G$ for an equation

  2. acts by increasing the rate of the forward reaction more than the reverse reaction

  3. raises the equilibrium constant of a system

  4. may have a molecular weight as low as $1$ or higher than $200,000$

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Correct Option: D
Explanation:

Gibbs free energy change is a state function which does not depend upon the path taken by the reaction whereas catalyst change path by lowering activation energy.

Catalysts increase the rate of the reaction but have no effect on the yield and catalysts speed up both forward and reverse reaction hence it doesn't change equilibrium constant.

Catalyst doesn't need to be so bulky otherwise instead of fastening the reactions it decreases the speed of reaction. But its weight can be as low as 1 or as high as 200000.

What can cause a decrease in activation energy?

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

  1. An increase in the reactant concentration

  2. An increase in the temperature

  3. A decrease in pressure

  4. Catalysts

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Correct Option: D
Explanation:

Option D is the correct answer.

Catalysts decrease the activation energy required for a chemical reaction and increase the rate of the reaction.

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.

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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.

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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

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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