Hold a thermometer in melting ice and it sticks stubbornly at zero, even as you keep heating. The energy is still flowing in, but instead of raising the temperature it is busy pulling the particles loose from their fixed positions.
A substance changes state at fixed temperatures: its melting point and its boiling point. During a change of state, energy is transferred but the temperature stays constant, because the energy is used to change the arrangement of the particles rather than to speed them up.
Melting is solid to liquid, boiling and evaporation are liquid to gas, condensing is gas to liquid, and solidifying (freezing) is liquid to solid.
The energy supplied goes into changing the arrangement of particles, not raising the temperature.
Add energy steadily and watch the temperature climb, then pause at each change of state.
Four quick checks. Each correct answer earns XP and lights this skill on your star map.
The change from solid to liquid is called...
The change from gas to liquid is called...
While a pure solid is melting, its temperature...
The energy supplied during melting is used to...
Each named change happens at a fixed temperature, shown as a flat section on a heating graph.
During a change of state the temperature stays constant. While ice melts or water boils you keep supplying energy, yet the thermometer does not rise, because the energy is changing the arrangement of particles, not their speed.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
A liquid cooling and turning into a solid is...
On a heating graph, the flat horizontal sections correspond to...
During boiling, the energy supplied...
Another thermal-properties skill down. Keep the chain going.