Order and Molecularity of a Reaction MCQ Quiz - Objective Question with Answer for Order and Molecularity of a Reaction - Download Free PDF

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.

K = 2.3 × 10⁵ L mol^-1 s^-1

For order of reaction,

The general formula for the unit of k is mol^1-n L ^n-1 s^-1

The unit of rate constant \(=\frac{\mathrm{mol} \mathrm{L}^{-1}}{\mathrm{~s}} \times \frac{1}{\left(\mathrm{~mol} \mathrm{~L}^{-1}\right)^n}\)

The unit ‘L mol^–1 s^–1 ’ corresponds to the 2nd-order reaction. 

CONCEPT:

Order of Reaction

• The order of a reaction is the power to which the concentration of a reactant is raised in the rate law equation.
• It is determined by the sum of the exponents of the concentration terms in the rate equation.
• The general rate law for a reaction aA + bB → products is given by:

  Rate = k[A]^x[B]^y

EXPLANATION:

• In the given reaction, the rate constant (K) has units of L mol^-1s^-1.
• The units of the rate constant for a second-order reaction are L mol^-1s^-1.
• For different orders of reaction, the units of the rate constant (k) are:
  • Zero order: mol L^-1s^-1
  • First order: s^-1
  • Second order: L mol^-1s^-1
  • Third order: L² mol^-2s^-1
• The given units of K (4.5 × 10^-4 L mol^-1s^-1) match the units for a second-order reaction.

Therefore, the order of the reaction is second.

Concept:

Molecularity: It is the number of reactant molecules involved in an elementary step of a reaction mechanism. Molecularity is always a whole number (e.g., unimolecular, bimolecular).

Order of Reaction: The order of reaction 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.

Explanation:

Statement 1: This is true. Molecularity is defined only for elementary reactions and is always a whole number.

Statement 2: This is incorrect. For an elementary reaction order and molecularity are same.

Statement 3: This is true. The order of a reaction can indeed be zero.

Statement 4: This is true. The order of a reaction is determined experimentally and is influenced by the mechanism proposed.

Conclusion:

The incorrect statement is: Order and molecularity of a reaction will not be same.

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.

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.

K = 2.3 × 10⁵ L mol^-1 s^-1

For order of reaction,

The general formula for the unit of k is mol^1-n L ^n-1 s^-1

The unit of rate constant \(=\frac{\mathrm{mol} \mathrm{L}^{-1}}{\mathrm{~s}} \times \frac{1}{\left(\mathrm{~mol} \mathrm{~L}^{-1}\right)^n}\)

The unit ‘L mol^–1 s^–1 ’ corresponds to the 2nd-order 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.

K = 2.3 × 10⁵ L mol^-1 s^-1

For order of reaction,

The general formula for the unit of k is mol^1-n L ^n-1 s^-1

The unit of rate constant \(=\frac{\mathrm{mol} \mathrm{L}^{-1}}{\mathrm{~s}} \times \frac{1}{\left(\mathrm{~mol} \mathrm{~L}^{-1}\right)^n}\)

The unit ‘L mol^–1 s^–1 ’ corresponds to the 2nd-order reaction. 

CONCEPT:

Order of Reaction

• The order of a reaction is the power to which the concentration of a reactant is raised in the rate law equation.
• It is determined by the sum of the exponents of the concentration terms in the rate equation.
• The general rate law for a reaction aA + bB → products is given by:

  Rate = k[A]^x[B]^y

EXPLANATION:

• In the given reaction, the rate constant (K) has units of L mol^-1s^-1.
• The units of the rate constant for a second-order reaction are L mol^-1s^-1.
• For different orders of reaction, the units of the rate constant (k) are:
  • Zero order: mol L^-1s^-1
  • First order: s^-1
  • Second order: L mol^-1s^-1
  • Third order: L² mol^-2s^-1
• The given units of K (4.5 × 10^-4 L mol^-1s^-1) match the units for a second-order reaction.

Therefore, the order of the reaction is second.

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.

K = 2.3 × 10⁵ L mol^-1 s^-1

For order of reaction,

The unit of rate constant \(=\frac{\mathrm{mol} \mathrm{L}^{-1}}{\mathrm{~s}} \times \frac{1}{\left(\mathrm{~mol} \mathrm{~L}^{-1}\right)^n}\)

The unit ‘L mol^–1 s^–1 ’ corresponds to the 2nd order reaction. 

K = 2.3 × 10⁵ L mol^-1 s^-1

For order of reaction,

The general formula for the unit of k is mol^1-n L ^n-1 s^-1

The unit of rate constant \(=\frac{\mathrm{mol} \mathrm{L}^{-1}}{\mathrm{~s}} \times \frac{1}{\left(\mathrm{~mol} \mathrm{~L}^{-1}\right)^n}\)

The unit ‘L mol^–1 s^–1 ’ corresponds to the 2nd-order reaction. 

Concept:

The order of a reaction can be deduced by examining how the half-life \(( t_{1/2} )\) varies with the concentration of the reactant. For a given reaction of order n:

• Zero-order: \(t_{1/2}\) is proportional to \([XY_3]\)

• First-order: \(t_{1/2}\) is independent of \([XY_3]\)

• Second-order: \(t_{1/2}\) is inversely proportional to \([XY_3]\)

• Third-order: \(t_{1/2}\) is inversely proportional to \([XY_3]^2\)

Explanation:

Given the data:

• At 100 mm, \(t_{1/2}\) = 8 hours

• At 200 mm, \(t_{1/2}\) = 4 hours

When the concentration doubles from 100 mm to 200 mm, the half-life is halved from 8 hours to 4 hours. This indicates that the half-life is inversely proportional to the concentration of the reactant.

For a reaction where the half-life is inversely proportional to the concentration, the reaction is second-order.

Conclusion:

The order of the reaction is 2.

K = 2.3 × 10⁵ L mol^-1 s^-1

For order of reaction,

The unit of rate constant \(=\frac{\mathrm{mol} \mathrm{L}^{-1}}{\mathrm{~s}} \times \frac{1}{\left(\mathrm{~mol} \mathrm{~L}^{-1}\right)^n}\)

The unit ‘L mol^–1 s^–1 ’ corresponds to the 2nd order reaction.