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

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.


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

In auto-catalysis, one of the ______ of the reaction acts as a catalyst.

  1. intermediates

  2. products

  3. reactants

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

 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 the auto catalysis.
In auto-catalysis, one of the products of the reaction acts as a catalyst.
For example, when oxalic acid is titrated with $\displaystyle KMnO _4 $ in presence of dil $\displaystyle H _2SO _4 $, the colour of $\displaystyle KMnO _4 $ first fades slowly and then faster due to the formation of $\displaystyle Mn^{2+} $ ions which act as auto catalyst.
$\displaystyle 2KMnO _4 + 3H _2SO _4 +5H _2C _2O _4 \rightarrow K _2O _4 +2MnSO _4 +8H _2O +10CO _2$

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.