Melting is the physical process by which a solid turns into a liquid after absorbing enough heat. This change of state occurs at a specific temperature called the melting point, which varies depending on the substance. For example, ice melts into water at 0°C (32°F), while metals like iron melt at much higher temperatures. ^[1-4]

What Happens During Melting

Melting is a type of phase change, which happens when the substance absorbs enough heat energy to overcome the intermolecular forces holding its particles together. Solids are made up of particles, such as atoms, ions, or molecules, that are tightly packed and vibrate about fixed positions. As heat is added, the kinetic energy of the particles increases. They begin to vibrate more rapidly until they can move past one another, allowing the solid to become a liquid. The temperature remains constant during the phase change because the added energy goes into breaking the bonds between particles instead of raising the temperature. 

Melting Point Values

The table below shows the melting point values of some common substances in both Celsius (°C) and Fahrenheit (°F) scales. ^[1-6]

Note: Glass does not have a sharp melting point but softens gradually over a range of temperatures.

Factors That Affect Melting ^[1-6]

1. Pressure

Pressure significantly influences the melting point of a substance. In most cases, increasing pressure raises the melting point because the particles are forced closer together, making it harder for them to break free into a liquid state.

However, water is an exception. Ice melts at a lower temperature under high pressure. This principle explains how ice skates work: the thin blade concentrates pressure on the ice, causing a thin layer to melt and create a slippery surface.

2. Impurities

The presence of impurities can lower the melting point, a phenomenon known as melting point depression. A common example is when salt is added to ice. The salt disrupts the orderly arrangement of water molecules, making it harder for them to maintain a solid structure. As a result, the ice melts at a lower temperature. This principle is widely applied in winter when salt is spread on roads to melt ice and prevent dangerous conditions.

3. Material Structure

The internal structure of a solid also affects its melting behavior.

• Crystalline solids, such as ice or table salt, have particles arranged in a regular, repeating pattern. These solids tend to have sharp, well-defined melting points because the structure breaks down abruptly when sufficient heat is applied.
• Amorphous solids, like glass or plastic, have a random arrangement of particles. Instead of melting at a specific temperature, they soften gradually over a range of temperatures. This gradual softening explains why glass does not have a sharp melting point but instead becomes increasingly flexible before becoming fully liquid.