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 chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

According to the adsorption theory of catalysis, the rate of reaction increases with the use of a catalyst because:

  1. the heat liberated during adsorption increases the rate of reaction

  2. the kinetic energy of reactants increases which increases the rate of reaction

  3. the activation energy of reaction increases which increases the rate of reaction

  4. the concentration of reactants at the active centers becomes high due to adsorption the rate of reaction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Adsorption theory of Heterogeneous catalysis involves five steps-

  • Diffusion of reactants to the surface of the catalyst.
  • Adsorption of reactant molecules on the surface of the catalyst. (Occurrence of chemical reaction on the catalyst’s surface through formation of an intermediate.
  •  Desorption of reaction products from the catalyst surface, and thereby,  making the surface available again for more reaction to occur.
  •  Diffusion of reaction products away from the catalyst’s surface.
  • So, we can deduce from Adsorption theory of catalysis that as the concentration of reactants at active centers increases due to adsorption and thus the rate of the reaction is also increased.

Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

The effectiveness of a catalyst is minimum at its optimum temperature.

  1. True

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

A catalyzed reaction rate is much faster at the optimum temperature of an enzyme. This is a result of increased catalyst activity due to its maximum effectiveness at the optimum temperature

Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

Incorrect statement about a catalyst is?

  1. It does not alter Gibbs energy, $\Delta G$ of a reaction

  2. it catalyses both spontaneous and non-spontaneous reactions

  3. A small amount of catalyst can catalyse a large amount of reaction

  4. It does not affect equilibrium constant of a reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

How do enzymes increase the rate of reaction?

  1. By lowering activation energy

  2. By increasing activation energy

  3. By changing equilibrium constant

  4. By forming enzyme substrate complex
Reveal answer Fill a bubble to check yourself
A 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.
Enzyme Catalysis - These are catalysts in the living system. Enzymes are substances which by their their presence, alter the rate of anybiological event. These are mainly proteins, and enzyme action is structure specific.

Enzyme catalysis is the increase in the rate of a chemical reaction by the active site of a protein. The protein catalyst (enzyme) may be part of a multi-subunit complex, and/or may transiently or permanently associate with a Cofactor (e.g. adenosine triphosphate). Catalysis of biochemical reactions in the cell is vital due to the very low reaction rates of the uncatalysed reactions. A key driver of protein evolution is the optimization of such catalytic activities via protein dynamics.


Enzymes are macromolecular biological catalysts. These are highly selective catalysts greatly accelerating both the rate and specificity of metabolic reactions. All enzymes are insoluble since they exist in the colloidal state. Urease is an enzyme that catalyzes the hydrolysis of urea, forming ammonia and carbon dioxide.
They decrease activation energy by providing alternate pathway for process and hence, increase the rate of reaction.

Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

Catalyst makes the reaction more exothermic.

  1. True

  2. False

  3. Ambiguous

  4. Data insufficient
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The statement is false.
Catalyst does not makes the reaction more exothermic.
A catalyst can lower the activation energy required for the reaction to take place and allows the reaction to reach equilibrium faster, but as the catalyst is unchanged at the end of the reaction, the total energy absorbed or released during the reaction will be the same.

Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

The temperature at which the catalytic activity of the catalyst is maximum, is called: 

  1. critical temperature

  2. room temperature

  3. absolute temperature

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

Some catalysts are, however, physically altered by a rise in temperature and hence their catalytic activity may be decreased. This is particularly true with colloidal solutions like that of platinum, since a rise in the temperature may cause their coagulation. In such a case, the rate of reaction increases up to a certain point and then gradually decreases. The rate of reaction is maximum at a particular temperature; that is Optimum temperature.

Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

Which one of the following statements is false?

  1. Enzymes arc highly specific

  2. Enzymes increase activation energy

  3. Enzymes require optimum temperature

  4. None of the above
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation
  • Enzymes serve as a biological catalyst by accelerating the rate of chemical reaction occurring inside the cells of living organisms, thus decreasing the activation energy required for the reaction to occur. 
  • Enzymes are very specific in nature, implying that, a particular enzyme can catalyze only a specific reaction and not all the reactions. 
  • The optimum temperature for an enzyme to function effectively is $37.5^o C$ which is also the normal human body temperature. At a temperature above this, enzymes undergo denaturation, thus, showing a reduced performance
Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

Which of the following catalysts is sensitive to temperature changes?

  1. Enzymes
  2. $Pt, Fe$
  3. $Ni, Fe$

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

Enzymes are specific in their action and catalyze reactions at lower temperature. At high temperature, they lose their specific nature and get denatured.

Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

A catalyst increases the rate of reaction by_________.

  1. Decreasing enthalpy

  2. Decreasing internal energy

  3. Decreasing activation energy

  4. Increasing activation energy
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A catalyst increases the rate of reaction by decreasing activation energy.
Note: The function of enzymes in the living system is to catalyse biochemical reaction.
Enzymes are highly substrate specific and catalyze reactions by providing an alternate pathway of lower activation energy.

Multiple choice chemistry surface chemistry enzyme catalysis catalysis proteins and enzymes

Which of the following factors are responsible for the increase in the rate of a surface catalysed reaction?
I. A catalyst provides proper orientation for the reactant molecules to react
II. Heat of adsorption of reactants on a catalyst helps reactant molecules to.overcome activation energy
III. The catalyst increases the activation energy of the reaction 
IV. Adsorption increases the local concentration of reactant molecules on the surface of the catalyst
Select the correct answer using the codes given below:

  1. I and II

  2. I and III

  3. I, II and IV

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

A catalyst works by providing an alternative reaction pathway to the reaction product. The rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.

Multiple choice chemistry metals effects of oxidation reactions in daily life corrosion of metals electroplating and its application

Reactions in which energy is absorbed are known as........... reactions.

  1. endothermic

  2. exothermic

  3. Synthesis

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

Endothermic reactions:
These are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. The temperature decrease can also be detected using a thermometer. 

Multiple choice chemistry particle nature, basic units history of atomic model atomic theory of dalton daltons atomic theory

Dalton viewed chemical change as :

  1. a transfer of electrons

  2. a transfer of protons

  3. a rearrangement of atoms

  4. a change of atoms from one type into another
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Dalton Atomic theory postulates-

1.  All matter is made up of atoms
2. All atoms of a given element are identical in mass and properties
3. Compounds are formed by combining two or more different kind of atoms.
4. A chemical reaction is a rearrangement of atoms.

Multiple choice chemistry nitrogen and sulfur ammonia and fertilizers preparation of ammonia-laboratory method and haber's process ammonia

As per Braun's principle, yield of Ammonia will be more in Haber's process under ______, conditions ($L=$ Low; $H=$ high; $T=$ Temp; $P=$ Pressure)

  1. $LT;LP$
  2. $LT;HP$
  3. $HT;HP$
  4. $HT;LP$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The manufacture of $NH _3$ by Haber's process is given as

${ N } _{ 2 }(g)+{ 3H } _{ 2 }(g)\rightleftharpoons { 2NH } _{ 3 }(g)\ \triangle 6H°=-92.4\ $
so, it is an exothermic reversible reaction and occurs with decrease in volume.
so, the low temperature will favour the forward reaction which is exothermic in nature
and since the reaction occurs with a decrease in volume .so, high pressure will favour the formation of of$NH _3$.

Multiple choice chemistry nitrogen and sulfur ammonia and fertilizers preparation of ammonia-laboratory method and haber's process ammonia

In the Haber process for the industrial manufacturing of ammonia involving the reaction
${ N } _{ 2 }(g)+3{ H } _{ 2 }(g)\rightleftharpoons 2{ NH } _{ 3 }(g)$ at $200atm$ pressure in the presence of a catalyst, a temperature of about ${ 500 }^{ o }C$ is used. This is considered as optimum temperature for the process because:

  1. yield is maximum at this temperature

  2. catalyst is active only at this temperature

  3. energy needed for the reaction is easily obtained at this temperature

  4. rate of the catalytic reaction is fast enough while the yield is also appreciable for this exothermic reaction at this temperature
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In order to yield the maximum yield of ammonia, the temperature is lowered though $500^oC$ is not a low temperature. This temperature $(500^oC)$ is a compromise temperature to produce reasonably a high proportion of ammonia in the equilibrium mixture in a very short time.

Multiple choice zoology energy flow in an ecosystem the energy pyramid ecological pyramid ecological pyramids

Pyramid of energy is always upright. This is in accordance with the law of 

  1. Thermodynamics

  2. Tolerance

  3. Limiting factors

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

Flow of energy declines as it passes from lower to higher trophic level. This is explained by second law of thermodynamics. According to this law, the energy decreases from one trophic level to the next trophic level because energy is lost as metabolic heat during transfer of energy. When food energy passes from producers to herbivores to carnivores, only 10% of energy is transferred from one trophic level to another trophic level. Hence, the pyramid of energy is always upright.

Thus, the correct answer is 'Thermodynamics.'