Consider a compound that has a melting point at 65 °C and a boiling point at 175 °C. Which of the following images represents a heating curve for the compound from 40 °C to 200 °C? (LO 11.5)

Verified step by step guidance

1. Step 1: Understand what a heating curve is. A heating curve is a plot of temperature versus time. It shows how the temperature of a substance changes as heat is added at a constant rate. The flat sections of the curve represent the phase changes, where the substance is transitioning from one state of matter to another (solid to liquid or liquid to gas). During these phase changes, the temperature remains constant.
2. Step 2: Identify the phase changes in the problem. The compound has a melting point at 65 °C and a boiling point at 175 °C. This means that the compound transitions from solid to liquid at 65 °C and from liquid to gas at 175 °C.
3. Step 3: Visualize the heating curve. The heating curve should start at a temperature below 65 °C (since the initial temperature is 40 °C), then rise until it reaches 65 °C, where it should remain flat as the compound melts. After all the solid has melted, the temperature should start to rise again until it reaches 175 °C, where it should remain flat as the compound boils. After all the liquid has boiled, the temperature should start to rise again until it reaches 200 °C.
4. Step 4: Compare the heating curve you visualized with the images provided. The correct image should match the description from step 3.
5. Step 5: Remember that the slope of the curve represents the rate of temperature change. The steeper the slope, the faster the temperature is changing. During phase changes (melting and boiling), the slope should be zero because the temperature is not changing.

Key Concepts

Heating Curve

A heating curve is a graphical representation that shows the change in temperature of a substance as it is heated over time. It illustrates the phases of matter (solid, liquid, gas) and the energy changes associated with phase transitions, such as melting and boiling. The curve typically features flat sections where phase changes occur, indicating that temperature remains constant while heat is added.

Phase Changes

Phase changes refer to the transitions between solid, liquid, and gas states of matter, which occur at specific temperatures and pressures. For the compound in question, melting occurs at 65 °C, transitioning from solid to liquid, while boiling occurs at 175 °C, transitioning from liquid to gas. Understanding these phase changes is crucial for interpreting the heating curve and identifying the correct representation.

Melting and Boiling Points

The melting point is the temperature at which a solid becomes a liquid, while the boiling point is the temperature at which a liquid becomes a gas. These points are characteristic of a substance and are influenced by intermolecular forces. In this case, the compound's melting point at 65 °C and boiling point at 175 °C are essential for determining the segments of the heating curve that correspond to solid, liquid, and gas phases.