Final answer:
Most substances change from a solid to a liquid state through a process called melting, where heat increases molecular energy, allowing molecules to move more freely over one another at the melting point.
Step-by-step explanation:
The process of a substance changing from a solid to a liquid state involves the increase in molecular energy as a result of heat being added to the system. As the temperature rises, individual molecules or atoms acquire enough energy to partially overcome the attractive forces holding them together in a solid form, allowing them to move past each other and resulting in a state known as the liquid phase. During this phase change, commonly known as melting, molecules do not slow down; they actually move more vigorously.
The transition from solid to liquid occurs at the substance's melting point, a specific temperature characteristic of that substance. At this point, the solid can transform into a liquid with a definite volume that can take the shape of its container because the molecules are still close enough to each other due to intermolecular forces. By contrast, the transformation into a gaseous state involves a much more significant increase in volume due to the much greater separation of particles.
This phase change happens because the added heat increases the energy within the molecules, allowing for greater movement and the overcoming of the intermolecular forces that otherwise keep the particles fixed in a solid structure.