Question:
Molecularity of a reaction:
Molecularity of a reaction:
Show Hint
Key distinctions between Order and Molecularity:
- Reaction Order: Experimental value, can be an integer, fraction, zero, or negative. Defined for any overall reaction.
- Molecularity: Theoretical integer count (\(1, 2, 3\)), never fractional or zero. Defined strictly for elementary reaction steps.
Updated On: Jul 4, 2026
- is always equal to the overall order of the reaction
- refers to the empirically found rate constant
- cannot have a fractional value
- refers only to non-elementary reaction
Show Solution
Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Concept:
Molecularity is a theoretical concept in chemical kinetics defined as the total number of reactant molecules, atoms, or ions that must collide simultaneously with proper orientation and sufficient energy to complete an elementary chemical reaction step.
Step 1: Identifying the core properties of Molecularity.
Let us evaluate the core physical properties of molecularity based on its definition as a count of colliding particles:
• Because molecularity represents a literal count of discrete molecules participating in a single collision step, it must always be represented by a positive integer value (e.g., unimolecular = 1, bimolecular = 2, termolecular = 3).
• It is physically impossible to have a fraction of a molecule undergo a collision step. Therefore, molecularity
cannot have a fractional value or be equal to zero. This matches statement (3) perfectly.
Step 2: Disproving the remaining incorrect options.
Let us analyze why the other statements are incorrect:
• Statement (1) is incorrect: The reaction order is an empirical quantity determined experimentally from the rate law, and it can be zero, fractional, or negative. The order matches the molecularity only for simple, single-step elementary reactions. For complex, multi-step reactions, the overall reaction order often differs from the molecularity of the individual steps.
• Statement (2) is incorrect: Molecularity is a theoretical count of colliding molecules; it does not describe the empirical rate constant ($k$).
• Statement (4) is incorrect: Molecularity is defined strictly for individual elementary reaction steps. For complex, non-elementary reactions that occur via multi-step mechanisms, the term molecularity has no meaning for the overall net reaction.
Thus, statement (3) is the uniquely correct statement.
Step 1: Identifying the core properties of Molecularity.
Let us evaluate the core physical properties of molecularity based on its definition as a count of colliding particles:
• Because molecularity represents a literal count of discrete molecules participating in a single collision step, it must always be represented by a positive integer value (e.g., unimolecular = 1, bimolecular = 2, termolecular = 3).
• It is physically impossible to have a fraction of a molecule undergo a collision step. Therefore, molecularity
cannot have a fractional value or be equal to zero. This matches statement (3) perfectly.
Step 2: Disproving the remaining incorrect options.
Let us analyze why the other statements are incorrect:
• Statement (1) is incorrect: The reaction order is an empirical quantity determined experimentally from the rate law, and it can be zero, fractional, or negative. The order matches the molecularity only for simple, single-step elementary reactions. For complex, multi-step reactions, the overall reaction order often differs from the molecularity of the individual steps.
• Statement (2) is incorrect: Molecularity is a theoretical count of colliding molecules; it does not describe the empirical rate constant ($k$).
• Statement (4) is incorrect: Molecularity is defined strictly for individual elementary reaction steps. For complex, non-elementary reactions that occur via multi-step mechanisms, the term molecularity has no meaning for the overall net reaction.
Thus, statement (3) is the uniquely correct statement.
Was this answer helpful?
0
0
Top TS PGECET Chemical Engineering Questions
- The degrees of freedom for a system consisting a gaseous mixture of \( N_2 \), \( H_2 \), and \( NH_3 \) is
- A bypass stream in a chemical process is useful, because it
- Sometimes in chemical processes, a part of the outlet stream is rejected as waste in order to keep the impurity level in the system within limits. This phenomenon is termed as
- In a chemical reaction the material balance calculation is based on
- The substance that appears in one incoming stream and outgoing stream which serves as reference for computations is called as a
View More Questions
Top TS PGECET Chemical Kinetics Questions
- The unit of frequency factor in Arrhenius equation is:
- For Arrhenius model of the rate constant \( k = k_0 \cdot e^{-E/RT} \), the graph drawn between \( \ln(k) \) versus \( \frac{1}{T} \) gives the slope of:
- The catalyst in a second order reversible reaction increases the rate of the:
- The unit of frequency factor in Arrhenius equation is:
- For Arrhenius model of the rate constant \( k = k_0 \cdot e^{-E/RT} \), the graph drawn between \( \ln(k) \) versus \( \frac{1}{T} \) gives the slope of:
View More Questions
Top TS PGECET Questions
- If \( P = \begin{pmatrix} 1 & 1 & 1 \\ 0 & 1 & 2 \\ 0 & 0 & 1 \end{pmatrix} \) is the modal matrix of \( A = \begin{pmatrix} 1 & 1 & 0 \\ 0 & 2 & 2 \\ 0 & 0 & 3 \end{pmatrix} \) then the sum of all the elements of \( P^{-1}AP \) is
- If the system of equations \( kx + y + z = k - 1 \), \( x + ky + z = k - 1 \), and \( x + y + kz = k - 1 \) has infinite solutions, then \( k \) is
- The value of the integral \( \int_C (2xy - x^2) \, dx + (x^2 + y^2) \, dy \) where \( C \) is the boundary of the region enclosed by \( y = x^2 \) and \( y^2 = x \), described in the positive sense, is
- Let \( f(x) = \log x \). The number \( C \) strictly between \( e^2 \) and \( e^3 \) such that its reciprocal is equal to \( \frac{f(e^3) - f(e^2)}{e^3 - e^2} \) is
- The solution of the differential equation \( (D^2 + 2)y = x^2 \) is
View More Questions