Chemistry · Physics

Thermodynamics and Chemical Kinetics

1,132 Questions

Thermodynamics and chemical kinetics are crucial branches of physical chemistry. This area focuses on energy transformations, reaction rates, equilibrium constants, and catalysts. These topics carry significant weight in competitive science and engineering examinations.

Enthalpy and energyChemical equilibriumEntropy conceptsReaction kinetics and catalysts

Thermodynamics and Chemical Kinetics Questions

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

Which of the following statements about catalyst is incorrect?

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Catalysts increase the rate of reaction by lowering activation energy, but they do not change the position of equilibrium or the amount of product formed at equilibrium.

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

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

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

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

A catalyst:

  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 $200,000$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

What can cause a decrease in activation energy?

  1. An increase in the reactant concentration

  2. An increase in the temperature

  3. A decrease in pressure

  4. Catalysts
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Option D is the correct answer.

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

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

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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

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

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

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

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

A catalyst:

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

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

Which of the following statements is more correct?

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

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

Which of the following statements is not true?

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

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

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

  1. inhibitor

  2. poison

  3. moderator

  4. promoter
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

Efficiency of the catalyst depends on its: 

  1. molecular weight

  2. number of free valencies

  3. physical state

  4. amount used
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

In chemical reaction, the catalyst: 

  1. alters the amount of product

  2. lowers the activation energy
  3. decreases $A$ of forward reaction
  4. increases $A$ of forward reaction
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

Which is not the characteristic of a catalyst?

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $\text{A}$

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

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

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