1. Heat Energy Absorption:
* When a solid absorbs heat energy, the particles within the solid start to vibrate more rapidly.
* This increased vibration causes the particles to break free from their rigid, fixed positions in the solid structure.
2. Weakening of Intermolecular Forces:
* As the particles vibrate more vigorously, the intermolecular forces (forces that hold the particles together) weaken.
* These forces are weaker in liquids than in solids.
3. Transition to a Liquid State:
* Once the heat energy absorbed is sufficient to overcome the intermolecular forces, the particles gain enough freedom to move around each other.
* This marks the transition from a solid to a liquid.
4. Maintaining Constant Temperature:
* During melting, the temperature of the substance remains constant. This is because the added heat energy is used to break the bonds between particles, not to increase their kinetic energy (and therefore temperature).
Factors Affecting Melting Point:
* Type of substance: Different substances have different melting points depending on the strength of their intermolecular forces.
* Pressure: Increased pressure generally raises the melting point.
* Impurities: Impurities can lower the melting point of a substance.
Example:
* Think of an ice cube melting. The heat from the surroundings causes the water molecules in the ice to vibrate faster, breaking free from their fixed positions and forming a liquid (water).
Key Points:
* Melting is a physical change, not a chemical change. The chemical composition of the substance remains the same.
* The melting point is the temperature at which a solid changes to a liquid.
