Chemistry ยท Physics

Thermodynamics and Chemical Kinetics

1,092 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
A catalyst remains unchanged chemically at the end of the reaction.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The given statement is true.
A catalyst remains unchanged chemically at the end of the reaction. It may take part in the reaction mechanism. It may be consumed in the first step and regenerated in the second step.

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

The catalyst is a substance which:

  1. increases the yield of the reaction

  2. increases the speed of the reaction

  3. decreases the speed of the reaction

  4. increases the speed of the reaction and remains unchanged.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Catalyst is a substance that changes (usually increases) the rate of a reaction, without being involved in the reaction. A catalyst provides large surface area to one of the reactants, providing it an exposure to be reacted upon by the other reactant.

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

Which of the following statements about catalysts is true?

  1. They increase the value of the equilibrium constant.

  2. They increase the amount of product present at equilibrium.

  3. They increase the concentration of the reactants.

  4. They are permanently altered as the reaction proceeds.

  5. They reduce the activation energy of the reaction.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Catalysts reduce the activation energy of the reaction by providing an alternate pathway having lower activation energy.
Thus, catalysts alter the mechanism of the reaction.

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

Which quantity increases with the addition of a catalyst ?

  1. Standard voltaic potential

  2. Entropy

  3. Enthalpy

  4. Reaction rate

  5. Gibbs free energy
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Reaction rate increases with the addition of a catalyst .
The catalyst increases the rate of forward as well as reverse reaction.
Hence, the equilibrium is quickly attained.

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

Find the false statement.

  1. The vapor pressure of a liquid decreases with increasing atmospheric pressure

  2. The value of an equilibrium constant is dependent on temperature

  3. The rate of a spontaneous reaction cannot be determined solely by its Gibbs free energy

  4. During a phase transition, the temperature of a substance must be constant

  5. The addition of a catalyst to a reaction at equilibrium has no net effect on the system

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

The incorrect statement is represented by option (A).
The vapour pressure of liquid depends on temperature and the mole fraction of solute. It does not depend on the atmospheric pressure.

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

Among the following which of the following statements is true?

  1. A catalyst cannot lower the activation energy.

  2. A catalyst can lower the activation energy

  3. A catalyst affect only the activation energy of the forward reaction

  4. A catalyst affects only the activation energy of the reverse reaction

  5. A calatyst is permanently changed after the activation energy is released
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A catalyst can lower the activation energy. It provides an alternate path for lower activation energy.

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

After the addition of a catalyst to an exothermic reaction, what happens?
I. The catalyst speeds up the reaction.
II. The catalyst slows down the reaction.
III. The catalyst increases the amount of product formed.

  1. I only

  2. II only

  3. I and II only

  4. II and III only

  5. I, II and III
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

After the addition of a catalyst to an exothermic reaction, the reaction speeds up. However, the amount of product formed does not increases.
A catalyst increases the rate of forward and forward reaction to equal extent. However it does not affects the value of the equilibrium constant.

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

Which of the following is not true about 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

A catalyst does increases the equilibrium constant of a reaction.
Thus, a catalyst does not affect the position of equilibrium.

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.