Short answer
Melting makes a solid become a liquid; dissolving makes a solute become part of a solution in a solvent. Ice becoming liquid water is melting, while sugar entering water is dissolving—the missing solid has a different destination in each case. 1 2
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At a glance
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| Question | Melting | Dissolving |
|---|---|---|
| What changes? | A substance’s solid state becomes liquid | A solute becomes incorporated into a solvent |
| What explains the change? | Molecular motion permits molecules to move past one another | Solvent molecules contact and pull apart the solute |
| Source example | Ice on aluminum | Sugar coating in water |
These contrasts describe the solid-and-liquid examples in the ACS lessons. 1 2
What each thing is
Melting is a phase change: the substance that was solid is now liquid. In the ACS ice model, water molecules leave their solid arrangement and can move past one another. Dissolving instead involves two roles, solute and solvent; the lesson examines sugar and salt entering water. 1 2
Key differences
The central distinction is the outcome, not whether warmth is involved. Melting produces the liquid state of the formerly solid substance. Dissolving places the solute in a solvent. Heating also affects dissolving, so a solid disappearing more readily in warm water is not, by itself, evidence that it melted. 1 2
How to tell them apart
Ask where the solid went: did it become its own liquid, or did it become incorporated into another liquid? That is a useful identification rule for these examples. Its limit is observation: seeing a solid shrink or vanish does not alone establish which destination applies. 1 2
Where they overlap
Both lessons explain visible changes through molecular motion and attractions. For melting, motion allows molecules to move past each other. For dissolving, solvent molecules interact with and pull on solute molecules. Their shared molecular vocabulary does not make the processes interchangeable. 1 2
Edge cases
Temperature is an especially misleading clue. The dissolving lesson shows that warmer water can accommodate much more sugar but only somewhat more salt. Neither observation should be relabeled melting merely because heating changes the result; temperature effects on dissolving also differ by substance. 2
Why the distinction exists
The terms answer different questions. “Melting” identifies a change in state, while “dissolving” identifies a solute–solvent process. Keeping them separate lets an explanation specify both what happened to the solid and which molecular interactions matter, rather than stopping at “it disappeared.” 1 2
Common misconceptions
“Disappeared” does not mean “melted,” and “warm water helped” does not settle the distinction. Another mistake is assuming all solids respond alike to warmer solvent: the supplied sugar-and-salt comparison explicitly shows different temperature responses. Those differences concern dissolving, not a switch in terminology. 1 2
Examples
First, the ACS demonstration places a small piece of ice on aluminum: its transformation into liquid water illustrates melting. Second, the dissolving lesson investigates an M&M’s sugar coating in water: sugar entering the water illustrates dissolving. This second example concerns the coating, not a claim that every part of the candy dissolves. 1 2