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 adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

The lowering of activation energy by catalyst is due to

  1. formation of adsorbed activated complex and to provide new pathway to reaction

  2. adsorption is always exothermic

  3. the adsorbed activated complex possesses lower energy level than simple activated complex

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

The lowering of activation energy by catalyst is due to formation of adsorbed activated complex and to provide new pathway to reaction.

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

According to adsorption theory of catalysis, the reaction rate increases, because:

  1. Adsorption produces heat which increases the rate of reaction

  2. In the process of adsorption, the kinetic energy of the molecules increases

  3. The concentration of reactants at the active centres becomes high due to adsorption

  4. The activation energy of the reaction becomes high due to adsorption
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Adsorption increases the reaction rate by concentrating reactant molecules on the surface of the catalyst, which increases the frequency of effective collisions. This is the fundamental principle of surface catalysis.

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

According to adsorption theory of catalysis, the speed of reaction increases because:

  1. the concentration of the reactant molecules at the active centres of the catalyst becomes high due to adsorption

  2. in the process of adsorption, the activation energy of the molecules becomes large

  3. adsorption produces heat which increases the speed of the reaction

  4. adsorption lowers the activation energy of the reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to adsorption theory of catalysis, the speed of reaction increases because the concentration of the reactant molecules at the active centres of catalyst becomes high due to adsorption.

Hence option A is correct.

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

According to the adsorption theory of catalysis,the speed of the reaction increase because :

  1. The concentration of reactant molecules at the active centers of the catalyst becomes high due to adsorption

  2. In the process of adsorption, the activation energy of the molecules becomes large

  3. Adsorption produces heat which increases the speed of the reaction

  4. Adsorption lowers the activation energy of the reaction.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The correct answer is $D$ . In the presence of catalyst the speed of reaction increases since the activation energy gets reduced and hence the rate of adsorption increases.

Multiple choice biology classification of living organisms binomial nomenclature nomenclature of organisms naming of the organisms nomenclature in classification

Which is correct about energy changes in living cells?

  1. First energy transfer, then energy transformation

  2. First energy transformation, then energy transfer

  3. Both occur discontinuously

  4. Both occur continuously
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The chemical energy from the organic molecules is transformed into a simpler form by cells through cellular respiration (Energy Transformation) and then transferred to other tissues of the body for their metabolic activities (Energy transfer). Both these processes happen continuously in our body.

The correct answer is D.

Multiple choice physics types of energy renewable and non-renewable resources renewable and non-renewable sources of energy production of electricity from solar energy

There will be an increase in potential energy of the system if work is done upon the system by

  1. any conservative or non-conservative forces

  2. a non-conservative force

  3. conservative force

  4. None of the these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since potential energy defined only for conservative force. It will increase for conservative force.

Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

In a case of catalytic reforming dehydration of naphthenes to aromatics is:

  1. favoured by a decrease in temperature and decrease in pressure

  2. favoured by an increase in temperature and increase in pressure

  3. favoured by an increase in temperature and decrease in pressure

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In catalytic reforming process, high octane number reformate is formed which is the main component of the motor, fuel, aviation gasoline or aromatic rich feedstock. Favourable Conditions for the reaction are High temperature, Low pressure and low space velocity.

Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

With increase in octane number:

  1. cetane number decreases

  2. activation energy increases

  3. both A & B

  4. neither A nor B
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Higher is the octane number higher is the activation energies. Activation energy is the amount of energy required to initiate combustion. 

Cetane number is the fuel's eagerness to ignite from the heat created in the bore from the compression of the air. Higher is the cetane number lower is the octane number.

Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

The activity of the catalyst in a semi-regenerative catalytic reformer is reduced over time during operation by:

  1. chloride loss

  2. carbonaceous coke

  3. both A and B together

  4. either A or B
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In catalytic reforming process, the noble metals platinum and rhenium are the catalysts used on a silica or silica-alumina support base. Fresh catalyst is chlorinated prior to use. On the other hand, an excessive chlorination could depress excessively the activity of the catalyst. Also in the case of the semi-regenerative catalytic reformer, the catalyst is reduced over time by carbonaceous coke deposition and chlorine loss.

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

Which of the following statements is incorrect?

  1. A second order reaction must be a bimolecular elementary reaction

  2. A bimolecular elementary reaction must be a second order reaction

  3. Zero order reaction must be a complex reaction

  4. First order reaction may be complex or elementary reaction.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A bimolecular elementary reaction may or may not be a Second Order Reaction whereas a Second Order reaction must be a bimolecular elementary reaction.

Ex: Decomposition of ${N} _{2}O _{5}$ is a 1st Order Reaction though its a bimolecular reaction.

Multiple choice zoology endocrine system and chemical co-ordination mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

A dehydration synthesis reaction is also known as

  1. A condensation reaction

  2. A hydrolysis reaction

  3. An isomeric reaction

  4. An energy-releasing reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Dehydration means removal of water. It is a synthesis reaction where polymerization occurs in which the monomers are bound together which releases water as the end product or byproduct.

Hence, the correct answer is 'A condensation reaction'.

Multiple choice biology chemical coordination and integration mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

Negative feedback occurs when

  1. The rate of a process increases as the concentration of product increases.

  2. The rate of process decreases as the concentration of product decreases.

  3. The rate of process decreases as the concentration of product increases.

  4. The rate of a process increases as the concentration of product decreases.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
  • A feedback mechanism for multistep reactions is a biological occurrence wherein the output of a system amplifies the system (positive feedback) or inhibits the system (negative feedback).
  • For example, Release of estrogen from the ovaries stimulates the secretion of GnRH from Hypothalamus which in turn stimulates the secretion of LH from anterior pituitary.when the levels of LH reaches above the normal levels in the blood it stimulates the release of progesterone from corpus luteum which causes the inhibition of the release of GnRH from the hypothalamus which in turn leads to inhibition of release of LH(product) from anterior pituitary and prevents the accumulation of LH(product)in blood. Hence negative feedback.
  • Hence Negative feedback occurs when The rate of process decreases as the concentration of product increases.
  • So, the correct answer is 'The rate of process decreases as the concentration of product increases'.
Multiple choice biology chemical coordination and integration mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

Negative feedback inhibition .......... the mechanism to reverse the changes.

  1. Activates

  2. Inactivates

  3. Remove

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • A feedback mechanism for multistep reactions is a biological occurrence wherein the output of a system amplifies the system (positive feedback) or inhibits the system (negative feedback).
  • For example, Release of estrogen from the ovaries stimulates the secretion of GnRH from Hypothalamus which in turn stimulates the secretion of LH from anterior pituitary.when the levels of LH reaches above the normal levels in the blood it stimulates the release of progesterone from corpus luteum which causes the inhibition of the release of GnRH from the hypothalamus which in turn leads to inhibition of release of LH(product) from anterior pituitary and prevents the accumulation of LH(product)in blood. Hence negative feedback.
  • Hence Negative feedback inhibition activates the mechanism to reverse the changes.
  • So, the correct answer is 'Activates'.
Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

Identify the energy changes in the following cases
$A$: A car moving up a hill.
$B$: Photographic film is exposed to sun-light.

  1. In $'A'$ mechanical energy in moving car is converted to kinetic energy and in $'B'$ potential energy is converted to chemical energy.
  2. In $'A'$ potential energy in moving car is converted to kinetic energy and in $'B'$ chemical energy is converted to light energy.
  3. In $'A'$ kinetic energy in moving car is converted to potential energy and in $'B'$ potential energy is converted to light energy.
  4. In $'A'$ kinetic energy in moving car is converted to potential energy and in $'B'$ light energy is converted to chemical energy.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$A$: A car moving up a hill.
Moving car has kinetic energy, kinetic energy gets converted to potential energy as it gains height $(h)$.
And potential energy $=mgh$
$B$: Photographic film is exposed to sun -light.
When photographic film is exposed to Sun the silver bromide present in it decomposes, such that the film cannot be developed, here the light energy changes to chemical energy.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

What are the various energy transformations that occur when you are riding a bicycle ?

  1. Muscular energy to kinetic and heat energy

  2. Mechanical energy to chemical and light energy

  3. Chemical energy to Internal energy

  4. Rotational energy to muscular energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

While riding a bicycle,the muscular energy of the rider gets transferred to heat energy and kinetic energy of the bicycle.Heat energy heats the rider's body.Kinetic energy provides a velocity to the bicycle to move in rotation.The transformation can be shown as:
Muscular energy$=$kinetic energy+heat energy
During transformation,the total energy remains conserved.