🔍 Key Concepts

• Latent heat of fusion is the heat added to change ice at 32°F to water at 32°F with no temperature change. • On a temperature vs. BTU graph, a phase change (solid ↔ liquid) appears as a horizontal line (temperature constant while heat input increases). • For water, fusion occurs at about 32°F, while vaporization occurs at about 212°F at atmospheric pressure.

💭 Think About

• On this diagram, which numbered line shows temperature staying at about 32°F while BTUs per pound are increasing? • Which segment marks the change from solid ice to liquid water without any increase in temperature? • Can you distinguish the fusion segment at 32°F from the vaporization segment at 212°F on the same graph?

✅ Before You Answer

• Verify which numbered line lies along the 32°F temperature mark while the horizontal axis (BTU per pound) increases. • Confirm that during this segment the phase is changing (ice to water) rather than just warming liquid or steam. • Make sure you do not mix up the latent heat of fusion (at 32°F) with the latent heat of vaporization (at 212°F) on the same curve.