Kinetics of Reaction MCQ Quiz in தமிழ் - Objective Question with Answer for Kinetics of Reaction - இலவச PDF ஐப் பதிவிறக்கவும்

CONCEPT:

Collision Frequency of Gas Molecules

• The collision frequency Z of gas molecules is a measure of how frequently gas molecules collide with each other.
• For gas molecules treated as hard spheres, the collision frequency is influenced by factors such as the number density, relative velocity, and the diameter of the molecules.
• The collision frequency Z can be approximated using the formula:

  \( Z \propto \frac{1}{\text{molecular radius}} \cdot \sqrt{\frac{\text{Temperature}}{\text{molecular mass}}} \)

EXPLANATION:

We have two gases A and B:

Molecule A: mass = m, radius = r

Molecule B: mass = 2m, radius = 2r

Since both gases are at the same temperature, we can compare their collision frequencies based on their mass and radius.

The collision frequency ratio Z_B : Z_A is given by:

\( \frac{Z_B}{Z_A} = \frac{\left( \frac{1}{2r} \right) \sqrt{\frac{T}{2m}}}{\left( \frac{1}{r} \right) \sqrt{\frac{T}{m}}} \)

\(\frac{Z_B}{Z_A} = \frac{1}{2} \cdot \frac{1}{\sqrt{2}} = \frac{2}{\sqrt{2}} : 1 \)

Therefore, the ratio of the collision frequency of B to that of A is 2/√2 : 1.

Conclusion:

So, the correct option is 2.

CONCEPT:

Relationship Between \(E_0\) and \(E_a\) in Collision Theory

• In collision theory, the rate constant \(k_{CT}\) for a bimolecular reaction is expressed as:
  • \(k_{CT} = N_A \left( \frac{8k_B T}{\pi \mu} \right)^{1/2} \sigma e^{-E_0}\)
• Here, \(E_0\) is the threshold energy, the minimum energy that reactant molecules must have to initiate the reaction. This energy is directly linked to the activation energy \(E_a\) in the Arrhenius equation.
• According to the Arrhenius equation:
  • \(k = A e^{-\frac{E_a}{RT}}\)
  •  

EXPLANATION:

• The relation between the threshold energy \(E_0\) and the activation energy (\(E_a\)) is typically given by:
  • \(E_a = E_0 + mRT\)
• Where:
  • \(E_a\) = activation energy
  • \(E_0\) = threshold energy
  • R = universal gas constant
  • T = temperature (in Kelvin)
  • m = constant, typically the power to which the temperature is raised (in this case,(\( m = \frac{1}{2})\)
• Thus, for this specific reaction, the relation becomes:
  • \(E_a = E_0 + \frac{RT}{2}\)
• Given the relation \(E_a = E_0 + \frac{RT}{2}\), we observe that the activation energy depends on both the threshold energy \(E_0\)and a temperature-dependent term \(\frac{RT}{2}\).
• This equation indicates that as the temperature increases, the activation energy also increases due to the term \(\frac{RT}{2}\), making it easier for molecules to overcome the reaction barrier.
• Based on this, the correct answer for the given question is:
  • \(E_a = \frac{RT}{2} + E_0\)

CONCLUSION:

• The correct answer is: Option 4

Concept:

Collision Theory: This theory states that chemical reactions occur when reacting molecules or atoms collide with sufficient energy and proper orientation. The minimum energy required for a successful reaction upon collision is called the activation energy.

Explanation:

Statement 1: This is true. Collisions are indeed a precondition for any reaction to occur, as per collision theory.

Statement 2: This is incorrect. Not all collisions result in the formation of products. Only collisions with sufficient energy and proper orientation (activated collisions) result in a reaction.

Statement 3: This is true. Only activated collisions, meaning those with sufficient energy and correct orientation, result in the formation of products.

Statement 4: This is true. Molecules need to acquire the activation energy to collide effectively for a reaction to occur.

Conclusion:

The incorrect statement is: All collisions result in the formation of the products.

Concept:

Order of reaction: It refers to how the concentration of reactants affects the rate of a chemical reaction. It is determined experimentally and may be zero, first, second, or even higher order. Here’s a brief overview of each type:

• Zero-order reaction: The rate of the reaction is independent of the concentration of the reactants. The rate law is typically expressed as: Rate=k

• First-order reaction: The rate of the reaction is directly proportional to the concentration of one reactant. The rate law is typically expressed as: Rate=k[A], [A] is the concentration of the reactant and k is the rate constant.

• Second-order reaction: The rate of the reaction is proportional to the square of the concentration of one reactant, or to the product of the concentrations of two reactants. The rate law can take forms like: Rate=k[A]² or Rate=k[A][B]

Explanation:

Statement 1: Order of a reaction can be known from experimental results and not from the stoichiometry of reaction.

The order of a reaction is determined experimentally by studying how the rate changes with concentration of reactants. It cannot be inferred solely from the stoichiometry of the reaction.

This statement is correct.

Statement 2: Overall molecularity of a reaction may be determined in a manner similar to overall order of reaction.

Molecularity refers to the number of molecules coming together to react in a single step. While molecularity is typically an intrinsic property of each elementary step in the reaction mechanism, for complex reactions it might be conceptualized in a similar manner to overall reaction order—but it's not a directly analogous concept. 

This statement is correct.

Statement 3: Overall order of a reaction \(mA + nB \rightarrow P\ is\ m + n \).

Order of the reaction is determined experimentally not by using the stoichiometry of the reaction.

This statement is correct.

Statement 4: Molecularity of a reaction refers to (i) each of the elementary steps in (an overall mechanism of) a complex reaction or (ii) a single step reaction.

Molecularity is a concept that applies to elementary reactions and refers to the number of reactant molecules involved in an elementary step. For complex reactions, it refers to each individual step, while for a single step reaction, it refers to that single step.

This statement is correct.

Conclusion:

Statements 1, 2 and 4 are correct.

Concept:

Second-order reaction: The rate of the reaction is proportional to the square of the concentration of one reactant, or to the product of the concentrations of two reactants. The rate law can take forms like:
Rate=k[A]², for 2A → Product

or Rate=k[A][B], for A+B → Product

Explanation:

Statement 1: The unit of the rate constant is concentration^-1 time^-1.

For a second-order reaction: Rate = k [A]²

This statement is correct.

Statement 2: t_½ is directly proportional to the initial concentration.

This means t_1/2 is inversely proportional to the initial concentration [A]₀, not directly proportional. This statement is incorrect.

Statement 3: The plot of 1/concentration versus time would give a straight line.

This indicates that a plot of \({\frac{1}{[A]}}\ versus\ time (t)\) would yield a straight line. This statement is correct.

Conclusion:

Thus statement 1 and 3 are correct.

\(2 \mathrm{NH}_3 \stackrel{\mathrm{Pt}}{\longrightarrow} \mathrm{N}_2+3 \mathrm{H}_2\)

As reaction is zero order

Rate = k[NH₃]⁰

Rate = k

Rate = \(\frac{-1}{2} \frac{\Delta\left[\mathrm{NH}_3\right]}{\Delta \mathrm{t}}=\frac{1}{3} \frac{\Delta\left[\mathrm{H}_2\right]}{\Delta \mathrm{t}}=\mathrm{k}\)

\(\frac{\Delta H}{\Delta t}=3 k\)

= 3 × 2.5 × 10^–4

= 7.5 × 10^–4 mol L^–1 s^–1

Correct answer: 2

Concept:

• Zero-order reactions are those in which the rate of reaction does not change when the concentration of the reactants increases or decreases.
• For a zero-order reaction, the rate law is given by,
• rate = k[A]⁰, where k is the rate constant.
• In the case of a zero-order reaction, the unit of rate constant k will be expressed in \({{{\rm{Concentration}}} \over {{\rm{Time}}}}\)

.

Explanation:

• The reaction is a zero-order reaction.
• The chemical reaction is given by,
• 2NH₃​→N₂+3H₂
• Now for a zero-order reaction, the rate of the reaction is equal to the rate constant (Rate=k).
• In a zero-order reaction, the rate constant is expressed as

                \({{{\rm{Concentration}}} \over {{\rm{Time}}}}\),

• The unit of concentration is \({{{\rm{Mol}}} \over {{\rm{L}}}}\) ​, and 's' is a unit of second.
• Thus the unit of k will be,\({\rm{k = }}{{{\rm{mol}}{\rm{/L}}} \over {\rm{s}}}\)
•   \({\rm{ = mol}}{\rm{.}}{{\rm{L}}^{{\rm{ - 1}}}}{\rm{.}}{{\rm{s}}^{{\rm{ - 1}}}}\)

Conclusion:

Hence, the rate constant for a zero-order reaction is molL-1s-1.

\(2 \mathrm{NH}_3 \stackrel{\mathrm{Pt}}{\longrightarrow} \mathrm{N}_2+3 \mathrm{H}_2\)

As reaction is zero order

Rate = k[NH₃]⁰

Rate = k

Rate = \(\frac{-1}{2} \frac{\Delta\left[\mathrm{NH}_3\right]}{\Delta \mathrm{t}}=\frac{1}{3} \frac{\Delta\left[\mathrm{H}_2\right]}{\Delta \mathrm{t}}=\mathrm{k}\)

\(\frac{\Delta H}{\Delta t}=3 k\)

= 3 × 2.5 × 10^–4

= 7.5 × 10^–4 mol L^–1 s^–1

Explanation:

The molecularity of an elementary reaction is defined as the number of reactant particles that come together to form the products in a single step.

In the given reaction, NH₄NO₂ is directly decomposing into N₂ and 2H₂O. Therefore, this is an elementary reaction, and its molecularity can be determined by counting the number of molecules or atoms that are involved in the reaction.

As we can see, NH₄NO₂ is the only reactant molecule in this reaction, and it is breaking down into two product molecules, N2 and 2H2O. Therefore, the molecularity of this reaction is one.

The reaction can be represented as:

NH₄NO₂ → N₂ + 2H₂O

where NH₄NO₂ is the reactant and N₂ and H₂O are the products.

This reaction is an example of a unimolecular reaction, where only one molecule of the reactant is involved in the reaction. The decomposition of NH4NO2 is a first-order reaction, where the rate of the reaction is proportional to the concentration of NH₄NO₂.

The reaction can be further explained by looking at the balanced chemical equation:

NH₄NO₂ → N₂ + 2H₂O

1 molecule of NH₄NO₂ → 1 molecule of N₂ + 2 molecules of H₂O

In conclusion, the molecularity of the given elementary reaction NH₄NO₂ → N₂ + 2H₂O is one, which means it is a unimolecular reaction where one molecule of the reactant is involved in the reaction.

Only one reacting species is involved, therefore it is a unimolecular reaction.

Explanation:

The molecularity of an elementary reaction is defined as the number of reactant particles that come together to form the products in a single step.

In the given reaction, NH₄NO₂ is directly decomposing into N₂ and 2H₂O. Therefore, this is an elementary reaction, and its molecularity can be determined by counting the number of molecules or atoms that are involved in the reaction.

As we can see, NH₄NO₂ is the only reactant molecule in this reaction, and it is breaking down into two product molecules, N2 and 2H2O. Therefore, the molecularity of this reaction is one.

The reaction can be represented as:

NH₄NO₂ → N₂ + 2H₂O

where NH₄NO₂ is the reactant and N₂ and H₂O are the products.

This reaction is an example of a unimolecular reaction, where only one molecule of the reactant is involved in the reaction. The decomposition of NH4NO2 is a first-order reaction, where the rate of the reaction is proportional to the concentration of NH₄NO₂.

The reaction can be further explained by looking at the balanced chemical equation:

NH₄NO₂ → N₂ + 2H₂O

1 molecule of NH₄NO₂ → 1 molecule of N₂ + 2 molecules of H₂O

In conclusion, the molecularity of the given elementary reaction NH₄NO₂ → N₂ + 2H₂O is one, which means it is a unimolecular reaction where one molecule of the reactant is involved in the reaction.

Only one reacting species is involved, therefore it is a unimolecular reaction.