Question

On a heating curve, the process of melting of a solid appears as:

• A. line with ${45}^o$ slope
• B. vertical line
• C. point
• D. horizontal line

Answer 1

Answer: (D)

horizontal line

The temperature of a system containing solid below its melting point will increase when heated. However, at the melting point, the temperature stops rising. At this temperature, the solid start to melt, and the heat is used to melt the ice. The melting of solid is called a phase transition. When energy supplied is used for the phase transition the temperature stays constant. After the phase transition is complete, the temperature rise will follow a different rate than that of the solid due to different heat capacity, as shown in the heating curve.

As energy absorbed is used for phase change, the heating curve appears a horizontal line in the transition phase like melting.

Hence, option $D$ is correct.