Chemistry · 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

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.

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

In case of autocatalysis: 

  1. reactant catalyses

  2. heat produced in the reaction catalyses

  3. product catalyses

  4. solvent catalyses
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Autocatalysis is the reaction where one of the products formed catalyzes the reaction. So in case of auto catalysis product catalyses the reaction. Hence catalysis of a reaction by one of its products is called autocatalysis.

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

Which of the following are correct about the catalyst?

  1. They participate in the reaction but recovered at last
  2. It does not affect $\Delta G $
  3. It increases $\Delta G $

  4. It alters the mechanism of reaction
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

The catalyst is the substance which increases the rate of reaction by lowering the activation energy which alters the mechanism of the reaction.

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

Which statement of the following is false for a catalyst?

  1. A catalyst can initiate a reaction.

  2. It does not alter the position of equilibrium in a reversible reaction.

  3. A catalyst remains unchanged in quality and composition at the end of the reaction.

  4. Catalysts are sometimes very specific in reaction.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst which is not consumed in the catalysed reaction and can continue to act repeatedly.It increase rate of forward as well as backward reaction.

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

In presence of a catalyst, the activation energy is lowered by 3 kcal at $27^o C$. Hence, the rate of reaction will increase by:

  1. 32 times

  2. 243 times

  3. 3 times

  4. 48 times
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$K={Ae}^{\dfrac{-Ea}{RT}}$ 

So Ratio, ${\dfrac{K _2}{K _1}}={e^\dfrac{(Ea _2-Ea _1)}{RT}}$
$\dfrac{K _2}{K _1}$=$e^{\dfrac{(3\times1000)}{(8.314\times300)}}$=$e^{{3000}/{2494}}$ = $e^{1.2}$ = $3.3$
Nearly 3 times.

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

An inhibitor is described as:

  1. a substance that slows down or stops a reaction

  2. a substance which inhibits the properties of a catalyst

  3. a substance formed during the reaction and does not participate in the reaction

  4. a substance which prevents formation of products in a reaction being most reactive
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A reaction inhibitor is a substance that decreases the rate of, or prevents, a chemical reaction. A catalyst, in contrast, is a substance that increases the rate of a chemical reaction.

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

Which of the following statements is/are correct ?

  1. The efficiency of a heterogeneous catalyst depends upon its surface area.

  2. Catalyst operates by providing alternate path for the reaction that involves a lower activation energy.

  3. Catalyst lowers the energy of activation of the forward direction without affecting the energy of activation of the backward direction

  4. Catalyst does not affect the overall enthalpy change of the reaction.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation
  • A catalyst that is in a separate phase from the reactants is said to be a heterogeneous, or contact, catalyst. An example of heterogeneous catalysis is the use of finely divided platinum to catalyze the reaction of carbon monoxide with oxygen to form carbon dioxide. The efficiency of a heterogeneous catalyst depends on the surface area, more the surface area more easier the catalysis occurs.
  • Collisions only result in a reaction if the particles collide with certain minimum energy called the activation energy for the reaction. A catalyst provides an alternative route for the reaction with lower activation energy. It does not "lower the activation energy of the reaction".
  • Lowering the Activation Energy of a Reaction by a Catalyst. The only effect of the catalyst is to lower the activation energy of the reaction. The catalyst does not affect the energy of the reactants or products. Thus it doesn't affect $\Delta H$.
Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

A catalyst in finely divided state is more efficient because in this state_______.

  1. It has got large activation energy

  2. It can react with one reactant more effectively

  3. It has large surface area

  4. All of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A catalyst in finely divided state is more efficient because in this state it has large surface area.
Higher is the surface area, higher is the catalytic efficiency and vice versa.