Question 34

The Correct Answer is B **Explanation for Option B (Correct):** The standard temperature/enthalpy diagram for water at atmospheric pressure shows five regions. Region 4 is the plateau where the temperature remains constant at 100°C (the boiling/condensation point). This plateau represents a phase change between liquid water and gaseous steam, requiring or releasing the latent heat of vaporization/condensation. Since the substance is undergoing **heat loss** (moving down the enthalpy scale), the process represented by Region 4 is condensation. In condensation, steam (gas) changes its physical state to become water (liquid) by losing its **latent heat of condensation**. **Why the Other Options are Incorrect:** * **A) Water absorbing its latent heat of vaporization and changing its physical state to become steam.** This process is boiling (vaporization) and represents a **heat gain** (enthalpy increase) in Region 4, the reverse of what is described in the question. * **C) Steam losing its specific heat and experiencing a drop in temperature.** This process occurs in Region 5 (superheated steam) and involves the specific heat of steam, not the latent heat associated with a phase change in Region 4. * **D) Water absorbing its specific heat and experiencing a rise in temperature.** This process represents heating liquid water and occurs in Region 3 (the sloping line between 0°C and 100°C). It is a process of **heat gain**, not heat loss.