Question

Which of the following best represents the temperature versus heat supplied graph for water, in the range of \(-20^\circ\text{C}\) to \(120^\circ\text{C}\)? 

• A. Graph 1
• B. Graph 2
• C. Graph 3
• D. Graph 4

Hint:

Flat portions in a temperature–heat graph always indicate a phase change where heat is absorbed without a rise in temperature.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The heating curve of water describes how the temperature changes as heat is added at a constant rate.
It involves segments of temperature increase (sensible heating) and segments of constant temperature (latent heating during phase transitions).
Step 2: Detailed Explanation:
1. Heating of Ice: From \(-20\ ^\circ\text{C}\) to \(0\ ^\circ\text{C}\), the temperature of ice increases linearly with heat supplied.
2. Melting of Ice: At \(0\ ^\circ\text{C}\), the temperature remains constant while the ice absorbs latent heat of fusion to convert into water. This creates the first horizontal plateau.
3. Heating of Water: From \(0\ ^\circ\text{C}\) to \(100\ ^\circ\text{C}\), the temperature of the liquid water increases linearly.
4. Boiling of Water: At \(100\ ^\circ\text{C}\), the temperature remains constant while the water absorbs latent heat of vaporization to convert into steam. This creates the second horizontal plateau.
5. Heating of Steam: Above \(100\ ^\circ\text{C}\), the temperature of the steam increases linearly.
Graph 3 correctly displays these two distinct plateaus at \(0\ ^\circ\text{C}\) and \(100\ ^\circ\text{C}\).
Step 3: Final Answer:
Graph 3 is the correct representation.