🔍 Key Concepts
• Section 4 is the horizontal line at about 212°F, where temperature stays constant while heat is added or removed.
• At a constant temperature during a liquid–vapor phase change, the heat involved is called latent heat rather than sensible heat.
• The direction of heat flow (adding heat vs removing heat) determines whether the process is called vaporization or condensation.
💭 Think About
• Look at the arrows in section 4: what do they suggest about whether the diagram is showing heating, cooling, or both?
• During boiling at 212°F, what name is given to the latent heat needed to change water at 212°F into steam at 212°F?
• If the exact same amount of heat is removed from steam at 212°F to turn it back into water at 212°F, what is that latent heat called? Are these two values different or the same on this kind of chart?
✅ Before You Answer
• Confirm that section 4 occurs at a constant temperature while BTU per pound is changing, indicating a phase change between liquid and vapor.
• Decide whether the chart is meant to represent only heating, or both heating and cooling, by checking the direction of the arrows in section 4.
• Ask yourself whether the heat represented there could correctly be described as latent heat of condensation, latent heat of vaporization, or both, depending on the direction of the process.