---
title: "A student investigates the kinetics of the reaction represented by the equation below at \\(450\\text{ K}\\):  \\[ \\text{NO}_2\\text{(g)} + \\text{CO(g)} \\rightarrow \\text{NO(g)} + \\text{CO}_2\\text{(g)} \\]  The student performs several trials at constant temperature and observes that doubling the initial concentration of \\(\\text{CO(g)}\\) while keeping the initial concentration of \\(\\text{NO}_2\\text{(g)}\\) constant has no effect on the initial rate of the reaction. Which of the following statements best explains why \\(\\text{CO(g)}\\) does not appear in the rate law for this reaction?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/123613/"
date_modified: "2026-09-28T12:01:44+00:00"
---

# A student investigates the kinetics of the reaction represented by the equation below at \(450\text{ K}\):

\[ \text{NO}_2\text{(g)} + \text{CO(g)} \rightarrow \text{NO(g)} + \text{CO}_2\text{(g)} \]

The student performs several trials at constant temperature and observes that doubling the initial concentration of \(\text{CO(g)}\) while keeping the initial concentration of \(\text{NO}_2\text{(g)}\) constant has no effect on the initial rate of the reaction. Which of the following statements best explains why \(\text{CO(g)}\) does not appear in the rate law for this reaction?

A student investigates the kinetics of the reaction represented by the equation below at \(450\text{ K}\):

\[ \text{NO}_2\text{(g)} + \text{CO(g)} \rightarrow \text{NO(g)} + \text{CO}_2\text{(g)} \]

The student performs several trials at constant temperature and observes that doubling the initial concentration of \(\text{CO(g)}\) while keeping the initial concentration of \(\text{NO}_2\text{(g)}\) constant has no effect on the initial rate of the reaction. Which of the following statements best explains why \(\text{CO(g)}\) does not appear in the rate law for this reaction?

- **A.** \(\text{CO(g)}\) does not participate in any step of the reaction mechanism because it acts only as an inert spectator species that provides collision surfaces for \(\text{NO}_2\text{(g)}\).
- **B.** \(\text{CO(g)}\) participates in the rate-determining step because a reaction order of zero indicates that collisions involving \(\text{CO(g)}\) require zero activation energy.
- **C.** \(\text{CO(g)}\) is completely consumed in an initial fast equilibrium step because reactants with a stoichiometric coefficient of \(1\) must react before the slow step begins.
- **D.** \(\text{CO(g)}\) participates in a fast elementary step that occurs after the rate-determining step because changing the collision frequency of a post-rate-determining step does not affect the overall reaction rate.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123613/*