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Collision theory of bimolecular gaseous reactions: NEET MCQs with answers

90 questions on this topic of Chemical Kinetics (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. Who among the following scientists developed the collision theory of bimolecular gaseous reactions?

  1. Peter Debye and Erich Hückel
  2. Svante Arrhenius and Jacobus van 't Hoff
  3. Max Trautz and William Lewis
  4. Wilhelm Ostwald and Walther Nernst
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Answer: (C) Max Trautz and William Lewis

Collision theory was developed by Max Trautz (1916) and William Lewis (1918). It provides an energetic and mechanistic insight into bimolecular gas-phase reactions.

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2. For a gaseous bimolecular reaction at 600 K, the activation energy Eₐ is 57.4 kJ mol⁻¹. What is the value of the fraction of collisions possessing energy greater than or equal to Eₐ? (Given: R = 8.314 J K⁻¹ mol⁻¹, e^(-11.51) = 1.0 × 10⁻⁵)

  1. 1.0 × 10⁻²
  2. 1.0 × 10⁻⁵
  3. 2.5 × 10⁻⁶
  4. 4.0 × 10⁻⁴
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Answer: (B) 1.0 × 10⁻⁵

The fraction of effective collisions possessing energy ≥ Eₐ is given by f = e^(-Eₐ/RT). Here, Eₐ/(RT) = 57400 / (8.314 × 600) = 57400 / 4988.4 ≈ 11.51. Thus, f = e^(-11.51) = 1.0 × 10⁻⁵.

hard

3. Given below are two statements: Statement I: The Boltzmann factor e^(-Eₐ/RT) represents the fraction of molecules that possess kinetic energy greater than or equal to the activation energy Eₐ at temperature T. Statement II: According to collision theory, the rate constant k can be represented as k = P · Z_AB · e^(-Eₐ/RT), where the product P · Z_AB corresponds to the pre-exponential factor A in the Arrhenius equation. In light of the above statements, choose the correct answer:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
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Answer: (A) Both Statement I and Statement II are correct

Statement I is correct: e^(-Eₐ/RT) corresponds to the fraction of molecules with energy equal to or greater than Eₐ. Statement II is also correct: comparing k = A · e^(-Eₐ/RT) with k = P · Z_AB · e^(-Eₐ/RT) directly shows that A = P · Z_AB.

medium

4. According to the collision theory, how does the collision frequency (Z_AB) between two gaseous reactants A and B vary with the absolute temperature (T) at constant volume?

  1. Z_AB is proportional to T
  2. Z_AB is proportional to √T
  3. Z_AB is proportional to T²
  4. Z_AB is independent of T
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Answer: (B) Z_AB is proportional to √T

From the kinetic theory of gases, the average velocity of gas molecules is proportional to the square root of the absolute temperature (√T). Since collision frequency Z_AB depends directly on the average relative velocity of colliding particles, Z_AB ∝ √T at constant volume.

easy

5. Who among the following scientists independently developed the collision theory of chemical reactions in 1916-1918?

  1. Svante Arrhenius and Jacobus van 't Hoff
  2. Max Trautz and William Lewis
  3. Peter Waage and Cato Guldberg
  4. Irving Langmuir and Fritz Haber
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Answer: (B) Max Trautz and William Lewis

Collision theory was developed by Max Trautz (1916) and William Lewis (1918). It is based on the kinetic theory of gases to explain rates of bimolecular gaseous reactions.

hard

6. For a gaseous bimolecular reaction A(g) + B(g) → C(g), the activation energy is 57.6 kJ mol⁻¹. At 300 K, what is the value of the energy factor e^(-Ea/RT)? (Given: R = 8.314 J K⁻¹ mol⁻¹, e^(-23.1) ≈ 9.3 × 10⁻¹¹)

  1. 1.8 × 10⁻¹⁴
  2. 4.2 × 10⁻⁸
  3. 9.3 × 10⁻¹¹
  4. 6.5 × 10⁻⁵
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Answer: (C) 9.3 × 10⁻¹¹

Ea = 57600 J mol⁻¹. The exponent is Ea/(RT) = 57600 / (8.314 × 300) = 57600 / 2494.2 ≈ 23.09 ≈ 23.1. Therefore, the fraction e^(-Ea/RT) = e^(-23.1) ≈ 9.3 × 10⁻¹¹.

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7. Consider the gaseous reaction: 2NO₂Cl(g) → 2NO₂(g) + Cl₂(g). If the reaction proceeds via bimolecular collisions between NO₂Cl molecules, why is the reaction rate far lower than predicted by simple collision theory (Rate = Z_AB · e^(-Eₐ/RT))?

  1. The collision diameter of NO₂Cl contracts at higher temperatures
  2. The mass of NO₂Cl leads to quantum tunneling that prevents bond breakage
  3. The activation energy decreases with an increase in collision velocity
  4. The colliding NO₂Cl molecules must have a proper relative spatial orientation for the chlorine atoms to interact
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Answer: (D) The colliding NO₂Cl molecules must have a proper relative spatial orientation for the chlorine atoms to interact

Simple collision theory does not account for molecular geometry. In NO₂Cl, for chlorine atoms to combine and eliminate Cl₂, the molecules must collide with a specific mutual orientation where the chlorine atoms approach each other; collisions with improper orientation are ineffective, necessitating the steric factor P << 1.

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8. Given below are two statements: Statement I: The value of the steric factor P is always greater than unity for bimolecular reactions involving polyatomic molecules. Statement II: Proper orientation ensures that existing bonds are broken and new bonds are formed smoothly during collision. In the light of the above statements, choose the correct answer:

  1. Both Statement I and Statement II are true.
  2. Both Statement I and Statement II are false.
  3. Statement I is true but Statement II is false.
  4. Statement I is false but Statement II is true.
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Answer: (D) Statement I is false but Statement II is true.

Statement I is false because for complex polyatomic molecules, only a small fraction of orientations are favorable, making P typically much less than 1 (P << 1). Statement II is true as correct spatial orientation brings the reacting atoms into direct contact to facilitate bond breaking and bond making.

hard

9. For a bimolecular gaseous reaction, if the absolute temperature is increased from 300 K to 310 K, the collision frequency Z_AB increases by approximately:

  1. 100%
  2. 1.6%
  3. 10%
  4. 50%
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Answer: (B) 1.6%

From the kinetic theory of gases, collision frequency Z_AB is proportional to √T. Therefore, Z₃10 / Z₃00 = √(310 / 300) = √(1.0333) ≈ 1.0165, which corresponds to an increase of about 1.65%. In contrast, the exponential fraction e^(-Eₐ/RT) increases by roughly 100-200%, showing that temperature accelerates rate via the exponential factor, not Z.

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10. Comparing the Arrhenius equation k = A · exp(-Eₐ/RT) with the modified collision theory expression k = P · Z_AB · exp(-Eₐ/RT), which of the following statements is correct regarding the pre-exponential factor A?

  1. A accounts for both collision frequency and proper orientation of reacting species
  2. A is independent of temperature, whereas Z_AB is proportional to T
  3. A corresponds exclusively to the fraction of molecules with energy greater than threshold energy
  4. A decreases exponentially with an increase in activation energy
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Answer: (A) A accounts for both collision frequency and proper orientation of reacting species

In the modified collision theory, the Arrhenius pre-exponential factor A is equated to P · Z_AB, where Z_AB represents the collision frequency and P (the steric or probability factor) accounts for the proper spatial orientation of colliding molecules.

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11. Which of the following expressions correctly relates the threshold energy (E_th), activation energy (E_a), and average kinetic energy of reactant molecules (E_R)?

  1. E_th = E_a + E_R
  2. E_th = E_a - E_R
  3. E_a = E_th + E_R
  4. E_R = E_th + E_a
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Answer: (A) E_th = E_a + E_R

Threshold energy is the minimum energy that reacting molecules must possess to undergo an effective collision. It equals the average kinetic energy of reactants plus the activation energy: E_th = E_a + E_R.

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12. Collision theory is most simply applied to:

  1. Bimolecular reactions of gaseous molecules treated as hard spheres
  2. Complex reactions in solution only
  3. Zero-order reactions only
  4. Nuclear reactions
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Answer: (A) Bimolecular reactions of gaseous molecules treated as hard spheres

The theory treats reactant molecules as hard spheres and is applied mainly to bimolecular gaseous reactions; it ignores the structure of molecules beyond the steric factor.

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