Melting vs Dissolving

Quick Answer

Melting is a solid turning into a liquid because of heat. Dissolving is a solid mixing into a liquid solvent without changing what it is.

What Each One Really Means

This one looks simple, but I have seen JSS students and even SS students mix it up. Let me settle it. Melting is a phase change. You apply heat to a solid, the particles gain enough energy to break free from their fixed positions in the lattice, and the solid becomes a liquid. Ice melts into water. Iron melts into molten iron. The substance is still the same thing. Same chemical identity, different physical state. Dissolving is different. You put a solid into a liquid, and the solid particles are pulled apart by the solvent and spread throughout. Sugar dissolves in water. Salt dissolves in water. But notice something important. The sugar does not become a liquid. The sugar molecules are still sugar. They are just surrounded by water molecules now. And dissolving does not require melting. You can dissolve salt in cold water. No heat needed. Now here is the trap. Some students think that when sugar dissolves, it melts first. No. It does not. Melting and dissolving are two completely different processes. Melting is about heat breaking a lattice. Dissolving is about solvent-solute interactions. One changes the state of the substance. The other just spreads it through a medium. If a question asks whether a solid changed into a liquid or mixed into a liquid, read carefully. The words change into and mix into are the clue.

Side-by-Side Comparison

Memory Device

Melting is change of state. Dissolving is change of location.

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