During the transformation of matter from the solid to the liquid state, the heat supplied does not produce a temperature increase because

1. Analyze the Question

The question asks why the temperature of a substance remains constant during the phase change from solid to liquid (melting), even though heat is being continuously supplied to it.

2. Explain the Concept

In physics, this phenomenon is known as Latent Heat of Fusion.

When a substance is in a solid state, its molecules are held together in a fixed, rigid structure by strong intermolecular forces. To transition from a solid to a liquid, these bonds must be overcome.

When you supply heat to a melting solid:

• The energy is not used to increase the kinetic energy of the molecules (which is what would cause a rise in temperature).
• Instead, the energy is used entirely to perform the work of breaking or weakening the intermolecular bonds that hold the solid structure together.
• Because the kinetic energy of the molecules remains unchanged during this process, the temperature remains constant until the entire substance has melted.

3. Show the Solution

• Step 1: Recognize that temperature is a measure of the average kinetic energy of the particles in a substance.
• Step 2: Identify that during a phase change (like melting), the substance is absorbing energy (latent heat).
• Step 3: Apply the principle of conservation of energy: Since the temperature is not rising, the energy supplied must be going into potential energy (breaking bonds) rather than kinetic energy.
• Step 4: Evaluate the options. Options A, B, and C describe processes that do not explain the constant temperature during phase change. Option D correctly identifies that the energy is consumed by the structural changes (breaking bonds).

4. Identify the Answer

The correct option is D. All the heat energy supplied is used as latent heat to overcome the intermolecular forces, allowing the solid to transition into a liquid without increasing the temperature.

5. Exam Tip

Remember the phrase: "Latent means hidden." When you see a flat line on a temperature-time graph during a phase change, know that the heat is "hidden" because it is working on the bonds, not the thermometer!