Heating Solids: Phase Changes Explained

When a solid material is heated continuously, it undergoes specific physical changes related to its state.

Solid Heating Process

• Initial Heating & Expansion: As heat energy is supplied, the particles within the solid vibrate more vigorously. This increased vibration typically causes the solid to expand slightly.
• Melting Point: With continued heating, the solid reaches its melting point. At this temperature, the particles have enough energy to overcome the forces holding them in fixed positions. The solid transforms into a liquid.
• Evaporation: If heating continues after the solid has completely melted into a liquid, the liquid will eventually reach its boiling point. At and above the boiling point, the liquid transforms into a gas through evaporation (or boiling). Some liquids can also evaporate slowly at temperatures below their boiling point.

Evaluating Options

• Option 1 (It shrinks) is incorrect as solids generally expand when heated.
• Option 2 (It evaporates directly) describes sublimation, which is specific to certain substances (e.g., dry ice) and not a general outcome for all solids upon heating.
• Option 3 (It melts and may later evaporate) accurately describes the typical sequence of phase changes for most solids when heated continuously: melting followed by potential evaporation.
• Option 4 (It expands and turns into a gas) is partially correct about expansion but assumes direct conversion to gas (sublimation) which isn't universally true. Melting is the intermediate step for most solids.

Therefore, the most accurate and general description of what happens when a solid is heated continuously is that it melts and may later evaporate.