Latentia

Meet Latentia, an ice cube that keeps soaking up heat while her thermometer refuses to budge.

When a solid melts, the heat you add goes into loosening the bonds that hold its crystal together, not into raising its temperature. The heat needed is Q = mL_f: the mass times the specific latent heat of fusion. Until the last bit has melted, a mix of ice and water at normal pressure stays at 0 °C.

For water ice, L_f is about 334 kilojoules per kilogram. Melting 1 kg of ice takes about 334 kJ, enough to warm that same kilogram of liquid water by roughly 80 °C. That is why ice is so good at keeping drinks cold.

Latent heat shows up in weather and climate too: the melting and freezing of large amounts of ice and snow absorbs and releases large amounts of energy.

The value depends slightly on pressure and on the substance; other materials have very different latent heats. The 0 °C melting point is for pure ice at one atmosphere.