What happens at the particle level when a solid changes to a liquid?

• A. Particles lose energy and move closer.
• B. Particles gain energy and overcome some bonds to slide past each other.
• C. Particles vanish.
• D. Particles increase in number.

Answer: (B)

Melting occurs when a solid gains enough energy for its particles to break some of the attractions between them and slide past one another. As heat is added, particles move faster and can overcome some bonds, allowing them to flow and form a liquid. The number of particles stays the same; they don’t disappear or multiply. Losing energy would make particles move more slowly and stay in a fixed position, which describes solidification, not melting. So the description that fits melting is: particles gain energy and overcome some bonds to slide past each other.