When a solid transitions into a liquid, it undergoes a physical change known as melting. This process transforms a substance from its rigid, fixed shape to a flowing state. Melting explains how familiar items like ice or chocolate change their form.
Solids: A Closer Look
At a microscopic level, solids are characterized by their constituent particles being tightly packed together in highly organized arrangements. These particles occupy fixed positions within a structure. Strong attractive forces, known as intermolecular forces, hold these particles firmly in place. The particles in a solid are not entirely static; they continuously vibrate around their stable points. This arrangement gives solids their definite shape and volume.
The Role of Heat Energy
Introducing heat energy to a solid increases the internal energy of its particles. As a solid absorbs heat, the kinetic energy of its particles increases, causing them to vibrate more vigorously within their fixed positions. This increased vibrational motion stretches and weakens the attractive forces holding the particles together. As heating continues, a specific temperature is reached where these vibrations become energetic enough to overcome the intermolecular forces. This temperature is defined as the melting point of the substance.
The Transformation: From Solid to Liquid
Once a solid reaches its melting point, the absorbed heat energy is no longer used to increase the temperature but instead goes into breaking the intermolecular bonds. This allows the particles to break free from their lattice structure. They no longer vibrate in fixed positions but can now slide past one another, forming a liquid. This energy absorbed during the phase change, without an increase in temperature, is called the latent heat of fusion. The substance now exhibits properties characteristic of a liquid, such as fluidity and the ability to take the shape of its container, while maintaining a definite volume.
Beyond Melting: What Happens Next?
If heat continues to be applied to the liquid, its temperature will begin to rise again as the particles gain more kinetic energy. Eventually, the liquid will reach its boiling point, where it transitions into a gaseous state through a process called vaporization. The reverse process of melting, where a liquid changes back into a solid, is known as freezing or solidification, and it occurs at the same temperature as the melting point. Examples of melting include butter softening in a warm pan.