---
title: "A pure molecular substance initially in the solid state is heated at a constant rate under an external pressure of \\(1.0\\text{ atm}\\). The temperature of the sample as a function of time is recorded, producing the heating curve shown in the graph.  Which of the following best describes the energy changes occurring within the substance during segment \\(\\text{IV}\\)?"
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/119800/"
date_modified: "2026-08-21T08:12:22+00:00"
---

# A pure molecular substance initially in the solid state is heated at a constant rate under an external pressure of \(1.0\text{ atm}\). The temperature of the sample as a function of time is recorded, producing the heating curve shown in the graph.

Which of the following best describes the energy changes occurring within the substance during segment \(\text{IV}\)?

A pure molecular substance initially in the solid state is heated at a constant rate under an external pressure of \(1.0\text{ atm}\). The temperature of the sample as a function of time is recorded, producing the heating curve shown in the graph.

Which of the following best describes the energy changes occurring within the substance during segment \(\text{IV}\)?

![A grayscale heating curve graph with a horizontal axis labeled 'Time (min)' and a vertical axis labeled 'Temperature (^{\circ}\text{C})'. The plot shows a single continuous solid black curve consisting of five distinct sequential linear segments: Segment \(\text{I}\) rises with a positive slope from the origin to a first horizontal level; Segment \(\text{II}\) is a horizontal flat line; Segment \(\text{III}\) rises with a positive slope from the end of Segment \(\text{II}\) to a second horizontal level; Segment \(\text{IV}\) is a horizontal flat line that is longer than Segment \(\text{II}\); and Segment \(\text{V}\) rises with a positive slope from the end of Segment \(\text{IV}\) upward to the right. Centered directly above each of the five segments are Roman numeral labels: '\(\text{I}\)', '\(\text{II}\)', '\(\text{III}\)', '\(\text{IV}\)', and '\(\text{V}\)'. No other curves, gridlines, labels, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787299942-qccrsc.jpg)

- **A.** The average kinetic energy of the particles increases while their potential energy remains constant.
- **B.** The average kinetic energy and potential energy of the particles both increase simultaneously at equal rates.
- **C.** The potential energy of the particles increases as intramolecular covalent bonds are broken at constant temperature.
- **D.** The potential energy of the particles increases as intermolecular attractions are overcome at constant temperature.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119800/*