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 botany ecosystem : structure and function energy flow in food chain food chain and energy flow energy flow in ecosystem

Choose the correct answers from the alternatives given .
Which of the following describes the first law of thermodynamics?

  1. Energy is neither created nor destroyed, but it can change into matter

  2. Energy is neither created nor destroyed, but it can change from one energy form to another

  3. Some useful energy is lost as heat whenever an energy transfer occurs

  4. Energy transfers are always 100% efficient in changing energy from one useful form to another
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The first law of thermodynamics says that energy can't be created or destroyed, but it can be changed. The law forms the basis of the principle of conservation of energy. This means that anything that uses energy is changing the energy from one kind of energy to another.

So, the correct option is 'Energy is neither created nor destroyed, but it can change from one energy form to another'.

Multiple choice botany ecosystem : structure and function energy flow in food chain food chain and energy flow energy flow in ecosystem

Which law states that, conversion of energy from one form to another is not 100% efficient?

  1. First law of thermodynamics

  2. Second law of thermodynamics

  3. Energy flow

  4. Biological system
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The second law of thermodynamics states that energy transfers are never 100% efficient, as some energy is always lost as heat during the conversion process.

Multiple choice botany organisms and their environment energy flow in food chain food chain and energy flow energy flow in ecosystem

Choose the correct answers from the alternatives given .
Endergonic reactions

  1. are always coupling reactions

  2. can only occur if there is an input of energy

  3. have products with less free energy than the reactants

  4. all of the above are correct
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Endergonic needs an input of energy to create the products, which have more free energy as a whole than the sum of free energy of each of the reactants. An example of this type of reaction in biology is photosynthesis. This process depends on the reaction to absorb energy in the form of sunshine from the surroundings for it to occur. 
So, the correct option is 'can only occur if there is an input of energy'. 

Multiple choice botany organisms and their environment energy flow in food chain food chain and energy flow energy flow in ecosystem

Choose the correct answers from the alternatives given .
A living organism represents stored energy in the form of chemical compounds When an organism dies, what happens to.that stored energy?

  1. All chemicals immediately lose their high-energy bonds

  2. All molecules immediately degrade into basic elements

  3. All energy immediately leaves, and that is. one manifestation that the organism is dead

  4. Chemical compounds in cells lose their organisation over time because there is no longer an input of energy to maintain the organised state
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

There is constant input of energy needed for all the activities that go inside a living organism. Food is the source of this energy. When an organism dies, these activities or reactions are stopped which results in loss of organisation of chemical compounds in cells. 

So, the correct option is 'Chemical compounds in cells lose their organisation over time because there is no longer an input of energy to maintain the organised state'.

Multiple choice chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

Which of these are spontaneous at higher temperature?

I : $2CuS\, +\, C\, \rightarrow\, 2Cu\, +\, CS _2$ 

II : $ 2CaS\, +\, C\, \rightarrow\, 2Ca\, +\, CS _2$ 

III : $ 2CuS\, +\, 3O _2\, \rightarrow\, 2CuO\, +\, 2SO _2$

Given that : $\Delta\,G^{\circ} _f$ (in $kJ$.$mol^{-1}$) for $CuS\, =\, -49$; $CS _2\, =\, 63.6$ ;  $CaS\, =\, -1320$; $CuO\, =\, -127.2$ and $SO _2\, =\, -300.4$ 

  1. $2CuS\, +\, C\, \rightarrow\, 2Cu\, +\, CS _2$
  2. $ 2CaS\, +\, C\, \rightarrow\, 2Ca\, +\, CS _2$
  3. $ 2CuS\, +\, 3O _2\, \rightarrow\, 2CuO\, +\, 2SO _2$

  4. None of these
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

What does a catalyst do?

  1. Alter the state of equilibrium.

  2. Decreases the activation energy.

  3. Increases collision frequency.

  4. Increases the average kinetic energy of reacting species.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Catalyst is a substance, which lowers the activation energy of reaction because it provides an alternate pathway for reaction. Also, it increases backward and forward reaction to the same extent. Due to this lower activation energy, equilibrium is attained faster.

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

Which of the following is the best way to speed up a chemical reaction?

  1. Make an effort to concentrate the reactants as best as possible

  2. Add a catalyst

  3. Cool the reaction down

  4. Increase the pressure on the system
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
5 ways to increase the reaction rate :
1. The nature of the reactants: A reaction between two gases would be faster than a reaction between to liquids or two solids.
2. Temperature:  The heat causes the particles to move quickly, and due to the Collision Theory,  the reaction will occur faster.
3. Concentration: The higher the concentration of a reactant, the quicker the reaction will occur. 
4. Surface Area: The more the particles are exposed, the faster it is for the other reactant to collide into the particles, meaning the reaction rate will increase.
5. Catalysts: Catalysts are substances that increase the rate of reaction by speeding up the reaction without being used up in the reaction.
Adding catalyst can most effectively speed up the chemical reaction. 
Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

A catalyst increases the rate of a reaction by:

  1. increasing the activation energy of the reaction
  2. increasing the value of rate constants $(k _f$ and $k _b)$

  3. increasing the enthalpy change of the reaction

  4. decreasing the enthalpy change of the reaction
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A catalyst increases rate of reacting by decreasing activation energy. and increasing the enthalpy change of the reaction

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.
$\displaystyle 2KMnO _4 + 3H _2SO _4 +5H _2C _2O _4 \rightarrow K _2O _4 +2MnSO _4 +8H _2O +10CO _2$