🔍 Key Concepts

• Latent heat vs. specific heat on a temperature‑enthalpy diagram • What it means when the line on the diagram is horizontal (constant temperature) versus sloping (changing temperature) • Direction of the arrows on the line in region 4 when the problem says there is a heat loss

💭 Think About

• Look closely at region 4: is the temperature changing or staying constant while heat is being added or removed? How does that relate to latent heat versus specific heat? • If the system is losing heat and staying at about 212°F, what phase change between water and steam occurs at this temperature at atmospheric pressure? • Compare region 4 with regions 3 and 5: which regions clearly show a temperature rise or fall, and which show only a change in BTU per pound without a temperature change?

✅ Before You Answer

• Verify whether the temperature along region 4 is approximately 212°F (boiling/condensing temperature at atmospheric pressure). • Determine if the process in region 4 involves a change of state (liquid ↔ vapor) or only a temperature change within a single phase. • Match the idea of heat loss at constant temperature with the option that describes losing latent heat rather than specific heat.