States of matter

Keep the heater on and watch the thermometer. It climbs, then stops dead at 0 °C while the ice quietly gives up its shape. Nothing is broken — that heat is going somewhere else.

Playable Class 11 · Chemistry Thermodynamics Values simplified for teaching

Chart · the heating curve

Temperature against total heat added. The two flat shelves are the melting and boiling points — and their lengths are drawn to scale, so the boiling shelf of water really is about seven times longer than the melting one.

Three things to try

Stop the heater exactly on the plateau. Switch it off mid-melt and the ice freezes again — the thermometer goes back down without ever reaching 0 °C from above.
Compare water with ethanol. Same heater, same mass. Ethanol melts twenty times sooner and gives up its bonds far more cheaply.
Send the temperature slider to the boiling plateau. It will land you in the middle of the phase change, half liquid and half vapour, not at the edge of it.

Substance

Controls

Heater 100% Heat in 0 kJ Temp −40 °C

Live readout

State: Solid
Temp.: −40.0°C
Heat in: 0kJ
Bonds broken: 0%

Why the thermometer stalls

Temperature measures how fast the particles are jostling. Melting does not need them to move faster — it needs them to stop holding on to each other. Every joule that arrives is spent prising the lattice apart, so none of it shows up as a higher reading.

That hidden energy is the latent heat. Water needs 334 kJ per kilogram to melt and 2 257 kJ per kilogram to boil — which is why steam burns are so much worse than hot-water burns.