---
title: "A student investigates two elementary bimolecular gas-phase reactions for removing a hypothetical contaminant, \\(\\text{X(g)}\\). The collision partner is either structural isomer \\(\\text{Y}_1\\text{(g)}\\) or structural isomer \\(\\text{Y}_2\\text{(g)}\\). Both experiments are performed at \\(400\\text{ K}\\), with an initial concentration of \\(0.010\\text{ M}\\) for each reactant.  | Property | Reaction with \\(\\text{Y}_1\\text{(g)}\\) | Reaction with \\(\\text{Y}_2\\text{(g)}\\) | |—|—:|—:| | Molar mass of collision partner | \\(72\\text{ g/mol}\\) | \\(72\\text{ g/mol}\\) | | Effective collision diameter | \\(0.50\\text{ nm}\\) | \\(0.50\\text{ nm}\\) | | Measured \\(E_a\\) | \\(40\\text{ kJ/mol}\\) | \\(40\\text{ kJ/mol}\\) |  Structural modeling indicates that the reactive atom of \\(\\text{Y}_2\\text{(g)}\\) is accessible over a smaller fraction of the molecular surface than the reactive atom of \\(\\text{Y}_1\\text{(g)}\\). Let \\(A_1\\) and \\(A_2\\) be the respective pre-exponential factors in the Arrhenius equation. Which prediction correctly compares reaction 2 with reaction 1?"
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date_modified: "2026-08-19T12:40:39+00:00"
---

# A student investigates two elementary bimolecular gas-phase reactions for removing a hypothetical contaminant, \(\text{X(g)}\). The collision partner is either structural isomer \(\text{Y}_1\text{(g)}\) or structural isomer \(\text{Y}_2\text{(g)}\). Both experiments are performed at \(400\text{ K}\), with an initial concentration of \(0.010\text{ M}\) for each reactant.

| Property | Reaction with \(\text{Y}_1\text{(g)}\) | Reaction with \(\text{Y}_2\text{(g)}\) |
|—|—:|—:|
| Molar mass of collision partner | \(72\text{ g/mol}\) | \(72\text{ g/mol}\) |
| Effective collision diameter | \(0.50\text{ nm}\) | \(0.50\text{ nm}\) |
| Measured \(E_a\) | \(40\text{ kJ/mol}\) | \(40\text{ kJ/mol}\) |

Structural modeling indicates that the reactive atom of \(\text{Y}_2\text{(g)}\) is accessible over a smaller fraction of the molecular surface than the reactive atom of \(\text{Y}_1\text{(g)}\). Let \(A_1\) and \(A_2\) be the respective pre-exponential factors in the Arrhenius equation. Which prediction correctly compares reaction 2 with reaction 1?

A student investigates two elementary bimolecular gas-phase reactions for removing a hypothetical contaminant, \(\text{X(g)}\). The collision partner is either structural isomer \(\text{Y}_1\text{(g)}\) or structural isomer \(\text{Y}_2\text{(g)}\). Both experiments are performed at \(400\text{ K}\), with an initial concentration of \(0.010\text{ M}\) for each reactant.

| Property | Reaction with \(\text{Y}_1\text{(g)}\) | Reaction with \(\text{Y}_2\text{(g)}\) |
|---|---:|---:|
| Molar mass of collision partner | \(72\text{ g/mol}\) | \(72\text{ g/mol}\) |
| Effective collision diameter | \(0.50\text{ nm}\) | \(0.50\text{ nm}\) |
| Measured \(E_a\) | \(40\text{ kJ/mol}\) | \(40\text{ kJ/mol}\) |

Structural modeling indicates that the reactive atom of \(\text{Y}_2\text{(g)}\) is accessible over a smaller fraction of the molecular surface than the reactive atom of \(\text{Y}_1\text{(g)}\). Let \(A_1\) and \(A_2\) be the respective pre-exponential factors in the Arrhenius equation. Which prediction correctly compares reaction 2 with reaction 1?

- **A.** \(A_2>A_1\), and reaction 2 has a greater initial rate, because steric shielding increases the frequency of energetic collisions.
- **B.** \(A_2=A_1\), but reaction 2 has a lower initial rate, because steric shielding increases the activation energy.
- **C.** \(A_2<A_1\), but the two reactions have equal initial rates, because their activation energies and temperatures are equal.
- **D.** \(A_2<A_1\), and reaction 2 has a lower initial rate, because a smaller fraction of collisions has the orientation needed for reaction.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119483/*